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  • Analytical Chemistry and Spectroscopy  (963)
  • 1980-1984  (963)
  • 1960-1964
  • 1925-1929
  • 1981  (963)
  • 101
    Electronic Resource
    Electronic Resource
    Enriched 13C NMR of a metallated α-sulphinyl ester; temperature effect (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 16 (1981), S. 273-279 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Lithium and magnesium enolates of an α-sulphinyl ester 83% 13C enriched at C-1 and C-2 are studied by 13C NMR at different temperatures. It is shown that two metaliated species are present in the case of lithium which exchange at -60°C, ΔG≠ -60° = 37.8 KJ mol-1 (9.05 Kcal mol-1) and that there is no rapid exchange between the non-metallated ester and the metallated species (on the NMR time scale). In the case of magnesium, two or three metallated species are formed, according to the temperature which do not exchange up to 0 °C.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270160405
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  • 102
    Electronic Resource
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    13C NMR specta of 4-quinolones and related compounds (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 16 (1981), S. 280-284 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Complete assignments are made for 23 4-quinolones and related compounds. Literature data are used to calculate chemical shifts for 17 of these compounds: calculated and experimental shifts are in excellent agreement - all within 5 ppm for nine of the compounds and a maximum discrepancy of 7.6 ppm.
    Additional Material: 5 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270160406
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  • 103
    Electronic Resource
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    13C NMR studies of reduced porphyrin compounds. Aromatic delocalization pathways (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 16 (1981), S. 290-295 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 13C NMR spectra of ms-tetraphenylchlorins, new aminoalkyl- and hydroxy-pyrroline substituted ms-tetra-phenylchlorins, and ms-tetraphenylisobacteriochlorins are presented and discussed. Significant changes in the chemical shifts of the α-pyrrole, α-pyrroline and meso skeletal carbons are found in chlorins and isobacteriochlorins in comparison to porphyrins. In contrast, the chemical shifts of the β-pyrrole carbons are almost unaffected by the structural modifications in chlorin and isobacteriochlorin. The chemical shifts of the α-pyrrole carbons in the various chlorins and isobacteriochlorins are strongly affected by the substitutents of the pyrroline ring, or by the introduction of an additional pyrroline ring in isobacteriochlorins. The results show that most of the electron density is concentrated in the unreduced part of the molecule, i.e. in the pyrrole rings and, especially, on the α-pyrrole carbons and is transferred or removed through the aromatic pathway by substituents on the pyrroline ring. These observations are supporting evidence that the α-pyrrole, α-pyrroline and meso-carbons are in the aromatic pathway and favour the proposal of a 16 atom dianion as the preferred delocalization pathway in chlorins and isobacteriochlorins.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270160408
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  • 104
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    The assignment of signals in the nitrogen NMR spectra of polycyclic diazines (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 16 (1981), S. 309-311 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 15N Nitrogen screening data are reported for some polycyclic azines and compared with previous results where available. INDO/S parameterized screening calculations for cinnoline and quinazoline help to decide between alternative nitrogen assignments. Nitrogen solvent shifts of several ppm are reported for all of the molecules studied.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270160411
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  • 105
    Electronic Resource
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    1H and 13C NMR study of tri-L-serine in aqueous solution (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 17 (1981), S. 214-216 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 270 MHz1H and 22.6 MHz13C NMR spectra of the tripeptide (L-Ser)3 dissolved in D2O have been measured and completely analysed as a function of pD in the region from 1.1 to 10. The pK(NH2)=7.0 is distinctly lower than common values for N-terminal residues. The chemical shifts for the peptide seryl residue change little with pD, with the H-β1 and H-β2 resonances being differently affected by the ionization of the COOH and NH2 groups. The 13C-α chemical shift in the peptide seryl residue exhibits a sequence effect which is considerably larger than expected on the basis of recently reported mean shifts. Rotational isomerism about the C-α—C-β bond is studied for the three different Ser residues on the basis of vicinal coupling constants 3J(H-α, H-β), and it is found that the population pb (-OH gauche to -CO-, and trans to -NH-) in the N- and p-Ser residues is notably larger than pb in Ser and Acetyl-Ser. In. C-Ser, In. C-Ser, pb is comparable to pb in Ser, but is twice as large as pb in AcSer.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270170317
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  • 106
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    Strained cyclobutane compounds: 1H NMR analysis of a new 1-substituted benzobicyclo[3.1.1]heptene system (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 17 (1981), S. 217-221 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 1H NMR spectra of a number of new derivatives of benzobicyclo[3.1.1]heptene were examined and interpreted by using a single set of coupling constants. All the compounds belonging to this system are in a γ-shaped configuration. Surprisingly, two different proton-proton spin-spin coupling constants (4J=5.5 to 6 Hz and 8.5 Hz) were obtained for the cyclobutane ring.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270170318
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  • 107
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    Carbon-13 NMR signals of some natural coumarins and their derivatives (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 17 (1981), S. 222-224 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 13C NMR spectra of the natural coumarins ostruthin, osthol, aegelinol (enantiomer of decursinol), luvangetin, seselin, anomalin, oxypeucedanin (and its enantiomer prangolarin) and oxypeucedanin hydrate and some of their derivatives have been studied. Self-consistent resonance assignments have been made following chemical shift theory and using simple models. Carbon-hydrogen coupling constants of some compounds are also reported. The alkoxy group/s at C-5 and/or C-8 in linear furocoumarins, as well as in linear pyranocoumarins, have unusually small shielding effects on the ortho- and para-carbons. This study also indicates that the C-4a and C-8 resonance assignments of osthol, made earlier, should be reversed.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270170319
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  • 108
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    Values and signs of 13C, 1H spin-spin coupling constants in 1,6,6aλ4-trithiapentalene and 1,6-dioxa-6aλ 4-thiapentalene (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 17 (1981), S. 225-226 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The values and signs of 13C, 1H spin-spin coupling constants in 1,6,6aλ4-trithiapentalene and 1,6-dioxa-6aλ4-thiapentalene have been re-investigated. The contributions from second order effects in the spectra have been included in an iterative spectral analysis. The values found deviate significantly from the values found earlier by first order analysis. The signs of the spin-spin coupling constants have been established by the use of the SPT technique.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270170320
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  • 109
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    1H and 13C NMR studies of some aromatic dilactones (precursors of paracyclophanes) (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 17 (1981), S. 227-231 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carbon-13 and proton NMR data of macrocyclic diaromatic dilactones are presented. The observed behaviour of the spectra as a function of temperature shows that the energy barrier for the re-orientation of the side chains is lower than 49 kJ mol-1 (12 kcal mol-1) and that the energy barrier for the rotation of the aromatic rings is larger than 99 kJ mol-1 (24 kcal mol-1). Hence, chiral substituted dilactones of this type will be resolvable, and the enantiomers can be easily handled at room temperature.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270170321
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  • 110
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    Carbon-13 NMR spin-lattice relaxation in dithiarsolanes. Correlation between molecular motions and structural properties (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 17 (1981), S. 285-289 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 13C NMR spin-lattice relaxation times (T1) and nuclear Overhauser enhancements (η) were measured for dithiarsolanes. The contributions of dipolar (T1DD) and spin-rotation (T1SR) mechanisms were determined. The T1 data were analysed to obtain information on the relative order of magnitude of the internal motion rates. The calculations were based on the isotropic, with internal rotation about the As—Ph bond, model of reorientation. In cis, trans-2-phenyl-4-methyl-1,3,2-dithiarsolane, the internal rotation of the phenyl ring is c. three times faster than overall molecular reorientation. The internal motion of the arsolane ring is slightly slower than the phenyl ring rotation. The rotation of the methyl groups in the compounds appears to be considerably hindered, with rotation energy barriers of c. 10 kJ mol-1. In contrast to the situation in the 4-methyldithiarsolane, the internal motion of the arsolane ring is twice as fast as the internal rotation of the phenyl ring for the methyl-unsubstituted analogue, 2-phenyl-1,3,2-dithiarsolane.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270170412
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  • 111
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    Natural abundance proton-coupled 15N NMR spectra of pyridines observed from proton polarization transfer experiments (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 17 (1981), S. 290-295 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Natural abundance proton-coupled 15N NMR spectra have been observed for pyridine and a series of mono- and disubstituted pyridines using polarization transfer achieved by the selective population transfer method. The magnitudes and signs of the 15N—1H spin-spin coupling constants between the ring-nitrogen and ring-protons are determined from complete iterative spectral analysis and/or selective population transfer experiments. Substituent effects on the 15N—1H coupling constants are discussed and compared with those for 13C—1H couplings in substituted benzenes.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270170413
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  • 112
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    Carbon-13 NMR parameters of phenyltin halogenides and phenyltin chalcogenides (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 17 (1981), S. 296-298 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 13C NMR shift parameters and couplings to tin are reported for nine phenyltin halogenides and seven phenyltin chalcogenides, as well as the T1 results for Ph2SnTe. A pronounced linear dependence of all coupling constants on the para-carbon shift is discussed.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270170414
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  • 113
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    Deuterium-induced 13C nuclear magnetic resonance isotope shifts and 13C—2H couplings for signal assignments and determination of deuteration site in cyclooctanone (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 17 (1981), S. 299-300 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Unambiguous signal assignments in the 13C spectra of monodeuterated cyclooctanones derived from the lead tetraacetate or silver oxide/bromine oxidations of the corresponding 1-monodeutero-alcohols have been obtained from deuterium-induced 13C isotope shifts and geminal and vicinal 13C—2H spin-spin coupling constants. The label in the ketones is shown to be in position 5.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270170415
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  • 114
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    Carbon-13 NMR spectra of some labdane diterpenoids (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 17 (1981), S. 301-302 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Carbon-13 signal assignments of the labdane diterpenoids phlogantholide-A, its diacetate and isophlogantholide-A are reported. The assignments of the 13C NMR signals of 14-deoxyandrographolide and its diacetate, made earlier, have now been confirmed by lanthanide shift studies on the former and also by 13C spectral studies on anhydroandrographolide diacetate and 14-deoxy-11,12-didehydroandrographolide diacetate.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270170416
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  • 115
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    15N chemical shifts as a conformational probe in enaminones15N NMR Spectroscopy, Part VIII. For Part VII, see Ref. 1. A variable temperature study at natural isotope abundance (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 17 (1981), S. 306-310 
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    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The high sensitivity of 15N shielding to the displacement of the lone pair electrons makes it a useful conformational probe for remote parts of a conjugated molecule. Thus, the chemical shifts are observed for different rotamers of enaminones in the slow exchange limit. The interpretation of the 15N chemical shifts in terms of the non-planarity of the E, s-E rotamers is in accord with 13C chemical shifts and 1J(CH) coupling constants.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270170418
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  • 116
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    A tropisomerism: Racemization barrier of 13-substituted oxyprotoberberines (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 17 (1981), S. 303-305 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The two possible conformations of 13-R-substituted oxyprotoberberines are enantiomeric. The racemization barriers are determined for three of these compounds (R=OMe, OCOMe, OCOPh) using variable temperature 1H NMR. It was found that ΔG203
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/mrc.1270170417
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  • 117
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    The mass spectra of some thiophene chalcone analogues (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 54-54 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210160118
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  • 118
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    Mass spectrometric fragmentation of the oxetanes of 3,5-dimethylisoxazole, 2,4-dimethylthiazole and 1-acetylimidazole (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 55-61 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mass spectra of the oxetanes of 3,5-dimethylisoxazole, 2,4-dimethylthiazole and 1-acetylimidazole have been studied with the aid of high resolution mass spectrometry. The spectra exhibit characteristic fragmentation patterns which are common to all these oxetanes and are classified as five processes.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210160202
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  • 119
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    The fragmentation of isotetronic acid O-methyl ethers under electron impact (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 68-71 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mass spectra of a series of methyl ethers of isotetronic acids have been examined and the modes of fragmentation rationalized on the basis of two general schemes.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/oms.1210160204
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  • 120
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    Thermal desorption of quasimolecular ions (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 72-75 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The thermal desorption of [M + Alkali]+ quasimolecular ions from a heated metal surface is reported for some alkali salts of carboxylic acids and mixtures of alkali halides with a crown ether, glucose and adenosine. No quasimolecular ion could be detected from sucrose. With benzo[15]crown-5 the desorption of [M + Na]+ ions takes place even below the threshold temperature for thermionic emission of alkali ions. In addition, the desorption of intact [B(C6H5)4]- ions from a layer of NaB(C6H5)4 is reported.
    Additional Material: 6 Ill.
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    URL: http://dx.doi.org/10.1002/oms.1210160205
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  • 121
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    The dependence of collision induced fragmentation pattern on the internal energy of the precursor ion (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 62-67 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A Method is presented whereby product organic ions formed as the result of fragmentation of metastable ions can be selected on the basis of their internal energies. The method requires requires angular collimation of the beam of reactant ions issuing from the ion source and that the fragmentation of the metastable ions is studied in the first field free region of a reversed geometry double focusing mass spectrometer. The product ions that make up the metastable peak are allowed to fall on the intermediate resolving slit and, by adjusting the magnet current over a small range, ions contained in different regions of the peak can be allowed into the second field free region. It is shown that the position of an ion within the metastable peak correlates with its internal energy, ions near the edges of the peak being the least excited. The ions entering the second field free region can be investigated by collisional activation. This has been done for molecular ions of p-chlorophenol, methylbenzoate, benzaldehyde, m-chlorotoluene and n-butane. The in which the collision induced fragmentation pattern varies with internal energy of the ions is illustrated.
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    URL: http://dx.doi.org/10.1002/oms.1210160203
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  • 122
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    Mass spectra of 2,2′-bridged biphenyls with 12-membered heterocyclic bridging rings: 2 - some tetrabenzo[b, d, h, j][1, 6]diazacyclododecines (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 123-124 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Mass spectra of four tetrabenzo[b, d, h, j][1, 6]diazacyclododecines are reported. The common pattern of fragmentation is altered by the presence of ortho methoxycarbonyl groups.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/oms.1210160305
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  • 123
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    Letter to the editor (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 144-144 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210160309
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  • 124
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    Site of protonation and bifunctional group interactions in α,ω-hydroxyalkylamines (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 176-179 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemical ionization mass spectrometry and mass analyzed ion kinetic energy spectrometry in conjunction with collision induced dissociation are used to study the fragmentation behavior of a series of α,ω-hydroxyalkylamines. The difference between the ionic population present at equilibrium in the source, and that which is sampled under nonequilibrium conditions, is revealed in the striking differences observed in product distributions in the chemical ionization mass spectra and the mass analyzed ion kinetic energy spectra. The major fragmentations in the mass analyzed ion kinetic energy spectra, loss of NH3 and H2O, show large variations in intensity as a function of the chain length between the hydroxy and amino functionalities. These results are rationalized through analysis of the relevant thermochemical data.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/oms.1210160407
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  • 125
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    Site of protonation and bond cleavages in chemical ionization mass spectrometry (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 188-188 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/oms.1210160410
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  • 126
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    Loss of methyl radical from some small immonium ions: Unusual violation of the even-electron rule (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 180-182 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several small immonium ions of general formula \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm R}^{\rm 1} {\rm R}^{\rm 2} {\rm C = }\mathop {\rm N}\limits^{\rm + } {\rm R}^{\rm 3} {\rm CH}_{\rm 3} $\end{document} (R1, R2, R3 = H or alkyl) eliminate .CH3; this reaction occurs in the mass spectrometer in both fast (source) and slow (metastable) dissociations. Such behaviour violates the even-electron rule, which states that closed-shell cations usually decompose to give closed-shell daughter ions and neutral molecules. The heats of formation of the observed product ions (for example, [(CH3)2C=NH]+.) can be bracketed using arguments based on energy data. Deuterium labelling results reveal that the methyl group originally bound to nitrogen is not necessarily lost in the course of dissociation. Thus, for instance, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{(CH}}_{\rm{3}})_2 = \mathop {\rm{N}}\limits^{\rm{ + }} {\rm{HCD}}_{\rm{3}} $\end{document} eliminates both CH3. and CD3., via different mechanisms, but very little CH2D. or CHD2. loss occurs.
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    Formation and structure of [C8H8O]+· ions, generated from gas phase ions of phenyl-cyclopropylcarbinol and 1-phenyl-1-(hydroxymethyl)cyclopropane (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 183-187 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The structure and formation of [C8H8O]+. ions generated from phenylcyclopropylcarbinol and 1-phenyl-1-hydroxymethylcyclopropane upon electron impact, have been studied using kinetic energy release measurements, by determination of ionization and appearance energies and by collisional activation. It is shown that the non-decomposing [C8H8O]+· ions have exclusively the structure of the enol ion of phenylacetaldehyde, although it is less stable than the enol ion of acetophenone by about 45 kJ mol-1. This has been interpreted as an indication that the [C8H8O]+· ions from phenylcyclopropylcarbinol are formed by an attack of either the phenyl ring or the hydroxyl group upon the C-1—C-2 (or C-1—C-3) bond of the cyclopropane ring under a simultaneous expulsion of ethene and migration of the attacking group to the C-1 position. The [C8H8O]+· ion from 1-phenyl-1-(hydroxymethyl)cyclopropane is formed by opening of the cyclopropane ring via a benzylic cleavage. A kinetically controlled hydrogen shift in the resulting ring opened ion prior to or during ethene loss then leads to the formation of [C8H8O]+· ions which have the structure of the enol ion of phenylacetaldehyde.
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    The use of the abbreviation MS/MS (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 280-280 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    Kinetic energy release during CO loss by rearrangement of α-acyl carbenium ions1 (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 279-280 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Tab.
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    Mass spectra of zoapatanol and montanol. Novel diterpenes from the mexican plant zoapatle (Montanoa tomentosa) (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 281-282 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 2 Ill.
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    The electron impact mass spectra of some spirobutenolides (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 283-284 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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    Forthcoming meeting (1981)
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    Biological Mass Spectrometry 16 (1981), S. 284-284 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Errata (1981)
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    Biological Mass Spectrometry 16 (1981), S. 284-284 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    Masthead (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981) 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 135
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    Electron impact induced migrations of aryl groups in substituted 4(3H)-quinazolinones (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 285-288 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electron impact mass spectra of 2-diphenylmethyl-3-aryl-4(3H)-quinazolinones display ions arising from migrations of different aryl groups in the molecular and [M—H]+ ions. The most abundant ion due to rearrangement, [C13H9NO]+·, is formed by migration of a phenyl from the benzhydryl group onto N-1 and subsequent cleavage of the heterocyclic ring. Other rearrangements involve initial migration of the N-3 aryl group to the benzylic carbon. The mechanisms of migrations were elucidated by means of deuterium and 15N labelling and are supported by metastable spectra.
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    Mass spectral behaviour of some m-dimethoxybenzene and sym-trimethoxybenzene sulphur derivatives (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 289-293 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mass spectra of fifteen m-dimethoxybenzene and sym-trimethoxybenzene sulphur derivatives (including thiols, sulphides, disulphides and trisulphides) have been investigated. Main fragmentation pathways have been proposed for each class of sulphur compound. Primary skeletal rearrangements of the molecular ions occurring in (poly)sulphur-bridged derivatives can provide a sensitive diagnostic tool both in structure elucidation and in the problem of locating methoxy substituents.
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    The formation of [CH3CH2C(=OH)CH2]+· from 1-hepten-3-ol (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 294-296 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The [C4H8O]+· ion in the mass spectrum of 1-hepten-3-ol is shown to be \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{3}} {\rm{CH}}_{\rm{2}} {\rm{C(= }}\mathop {\rm{O}}\limits^{\rm{ + }} {\rm{H}})\mathop {\rm{C}}\limits^{\rm{.}} {\rm{H}}_{\rm{2}} $\end{document} by collisional activation spectra, appearance energies and comparison of the ratios of the intensities of metastable decompositions. [C4H8O]+· appears to be formed by rearrangement of ionized 1-hepten-3-ol to \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{3}} \mathop {\rm{C}}\limits^{\rm{.}} {\rm{HC(= }}\mathop {\rm{O}}\limits^{\rm{ + }} {\rm{H)CH}}_{\rm{2}} {\rm{CH}}_{\rm{2}} {\rm{CH}}_{\rm{2}} {\rm{CH}}_{\rm{3}} $\end{document} followed by γ-hydrogen rearrangement-β-cleavage.
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    Mass spectrometry of metal compounds. Evidence of C—O cleavage in and effect of temperature on the mass spectra of chloropentacarbonylmanganese (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 303-305 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mass spectrum of Mn(CO)5Cl has been studied at 70 eV and at varying inlet temperatures of 20-250°C. Like the heavier metal carbonyl derivatives, Mn(CO)5Cl exhibits peaks due to carbido fragments. The spectrum run at 100°C shows the characteristic pattern of Mn2(CO)10 which originates from the formation and recombination of the Mn(CO)5 radical. The spectral pattern changes further at an elevated temperature (250°C) showing the formation of Mn2(CO)8Cl2. The effect of pyrolysis has been discussed.
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    Assigning structures to [C2H3O]+ ions (1981)
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    Biological Mass Spectrometry 16 (1981), S. 306-308 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The problem of assigning structures to [C2H3O]+ ions produced from a wide variety of precursor molecules has been readdressed. The identification of the acetyl cation, \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{3}} \mathop {\rm{C}}\limits^{\rm{ + }} = {\rm{O}} $\end{document}, from metastable peak characteristics and collisional activation mass spectra appears to be straightforward. The structure \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{2}} = \mathop {\rm{C}}\limits^{\rm{ + }} - {\rm{OH}} $\end{document} is also known to exist as a stable ion. A third ion, whose structure may be represented as \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm{C}}\limits^{\rm{ + }} {\rm{H}}_{\rm{2}} {\rm{CHO}} $\end{document} or has also been characterized.
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  • 140
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    Four isomers of [C3H8O]+· distinguished by collisional activation (1981)
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    Biological Mass Spectrometry 16 (1981), S. 309-311 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Collisional activation of the molecular ions of 1-propanol, 2-propanol and methyl ethyl ether, and of the m/z 60 ion from 1,2-dimethoxyethane provides evidence for four distinct forms of [C3H8O]+·. Collision induced decompositions may be explained either by simple cleavages, by cyclic processes involving adjacent substituents, or by bicyclic processes of adjacent substituents. Evidence for a form of [C3H8O]+· in which charge and radical site are separate is assembled from the spectra.
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    A caution on the use of metastable ions to assign fragmentation pathways (1981)
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    Biological Mass Spectrometry 16 (1981), S. 323-324 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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    Interference peaks in metastable ion spectra (1981)
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    Biological Mass Spectrometry 16 (1981), S. 325-326 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 3 Ill.
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    Studies of consecutive reactions of quinones in a reversed geometry mass spectrometer (1981)
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    Biological Mass Spectrometry 16 (1981), S. 312-322 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Consecutive reactions involving the ejection of molecules of carbon monoxide from quinone systems have been studied. Using a reversed geometry double focusing mass spectrometer, the individual steps of a consecutive reaction may be separated into different field free regions. The structure of ions formed in the ion source may be compared with those formed from the fragmentation of metastable ions in a field free region by studying differences in the pattern of translational energies released when they break. In the case of anthraquinone it is found that two structures exist for the [M—CO]+· ion. Critical energy measurements strengthen this argument. Furthermore, 18O labelling has been used to distinguish between the loss of carbon monoxide from different positions on the molecular ion of 1-hydroxyanthraquinone.
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    On the structure of the odd electron [C2H6O]+· ions in the mass spectrum of [1,3-propanediol]+· (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 326-327 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Tab.
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    The mass spectra of some substituted ethyl cinnamates (1981)
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    Biological Mass Spectrometry 16 (1981), S. 328-329 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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    Mass spectra of hexahydropyrrolobenzodiazepines (1981)
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    Biological Mass Spectrometry 16 (1981), S. 329-330 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    Masthead (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981) 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    Negative chemical ionization mass spectrometry of explosivesPresented in part at the 11th Meeting of the British Mass Spectroscopy Group, Canterbury (1980). (1981)
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    Biological Mass Spectrometry 16 (1981), S. 331-335 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The negative chemical ionization mass spectra of nitrobenzene, ethylene glycol dinitrate and nitroglycerine have been obtained using various reagent ions. For nitrobenzene, [OH]- gives the [M - H]-, together with [M]-· ions formed by electron capture, but other reagent ions gave relatively low intensity adduct peaks. Ethylene glycol dinitrate and nitroglycerine gave abundant [M + X]- ions (X = NO2, NO3, Cl, Br, I), together with ions arising from the thermal decomposition of the samples in the heated inlet system. The rate of anion attachment to these compounds is much greater than that to related compounds having only one functional group, and it is suggested that this is due to the participation of the adjacent groups in the bonding between the substrate and anion.
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    Anionization of volatile molecules on the surface of electrolytic solutions exposed to high electric fields (1981)
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    Biological Mass Spectrometry 16 (1981), S. 336-338 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The anionization of molecules supplied from the gas phase onto a negatively charged [Cl]- or [NO3]- ion donating surface has been investigated. The charged surface was prepared by exposing an aqueous solution of LiCl (or LiNO3) and polyethylene oxide to a high external field as is done in negative ion field desorption mass spectrometry. The ionization of some monosaccharides and adenosine by [Cl]- and [NO3]- attachment and of some acids by proton abstraction is reported.
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    Ion cyclotron resonance studies of ambident nucleophiles. The reactions of the trimethylsilyl cation with alkenyl ethers and alkoxy ketones (1981)
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    Biological Mass Spectrometry 16 (1981), S. 339-343 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
    Notes: Alkenyl ethers react through oxygen with Me3Si+ to yield intermediates which undergo characteristic fragmentations. In the particular case of allyl ethers, the decomposing adduct undergoes several fragmentations through the allyl substituent via 6-membered transition states. The reaction between Me3Si+ and alkoxy carbonyl derivatives yields both ‘ether’ and ‘keto’ adducts, characterized by their fragmentation patterns. The ‘ether’ adducts formed from Me3Si+ and alkoxy acetones undergo the same basic eliminations as those observed for the allyl ether/Me3Si+ systems.
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    Stable adduct formation during the gas phase reactions between the trimethylgermanium cation and organic nucleophiles. An ion cyclotron resonance studyAlso Part CXL in the series ‘Electron Impact Studies’. Part CXXXIX. Org. Mass Spectrom. 16, 339 (1981). (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 344-346 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Topics: Chemistry and Pharmacology
    Notes: The trimethylgermanium cation (Me3Ge+) reacts with aliphatic organic neutrals (M) which contain N, O or S, to form adducts [M + Me3Ge+] in the gas phase. These adducts are more stable than their analogues formed from the trimethylsilyl cation, and thus Me3Ge+ is a useful analytical reagent for chemical ionization mass spectrometry.
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    A study of the tautomerism of 5-as-triazinones by mass spectrometry (1981)
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    Biological Mass Spectrometry 16 (1981), S. 347-350 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The tautomeric equilibria of variously substituted 5-triazinones have been studied by comparing their mass spectra with those of their methylated derivatives. The results for 6-methyl-5-triazinone have been confirmed by comparison with the mass analysed ion kinetic energy spectra of ions generated from N-ethyl derivatives. The equilibria are dependent upon the nature of the substituents in the 3- and 6-positions.
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    Stereochemical effects in electron impact mass spectra of cis-trans isomeric 1,2,4,5-tetramethylcyclohexanes (1981)
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    Biological Mass Spectrometry 16 (1981), S. 358-360 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mass spectrometric fragmentation of the five cis-trans isomeric 1,2,4,5-tetramethylcyclohexanes is influenced by their configuration. The thermochemically stable isomers show a higher abundance of the [M—CH3]+ ions and a lower abundance of the [M—C2H5]+ ions than the strained isomers. The [M—CH3]+/[M—C2H5]+ intensity ratio correlates with the enthalpy difference ΔHisom and with the mean number of gauche arrangements ZgI of the stereoisomers.
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    Ion current surface for a double focusing mass spectrometer of reversed geometry (1981)
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    Biological Mass Spectrometry 16 (1981), S. 351-357 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Ion currents obtained for fragmentations in a mass spectrometer of reversed geometry have been represented as three-dimensional surfaces, which are termed ‘ion current surfaces’. In addition to ion current, useful dimensions of the ion current surfaces are a parameter ln(|ρ|) where ρ = (V0/V)(E/E0) and a parameter ln(|m*|) where m* = (V0/V)mB. Each ion reaction occurring in the source and flight path gives rise to a pattern of peaks and ridges on the surface. If the major features of the surface corresponding to each ion reaction are projected onto the zero ion current plane, they are disposed in a characteristic trapezoidal pattern. All simple and linked modes of scanning correspond to cross-sections of the surfaces, and representing the scanning modes in this light facilitates the identification of ‘cross-talk’.
    Additional Material: 12 Ill.
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    The mass spectra of some para substituted 2-(1-aryl-1-hydroxymethyl)-1-tetralones (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 375-375 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Tab.
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    Masthead (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981) 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1002/oms.1210160901
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  • 157
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    Mass spectrometry of pyrazolium salts (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 377-380 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of pyrazolium bromides were investigated by field desorption, field ionization and electron impact mass spectrometry. Dealkylation was found to be the predominant thermal decomposition. The nature of the substituents controls the pyrazole formed. The application of field ionization was found to facilitate the interpretation of the thermolytic decomposition products. Field ionization and electron impact mass spectra of N-phenylpyrazole and N-benzylpyrazole were obtained.
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  • 158
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    Acid catalyzed aldol condensation in the gas phase (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 381-382 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The gas phase reaction of acetaldehyde with a Brønsted acid in a chemical ionization source yields protonated crotonaldehyde, as shown by its collisional activation mass spectrum. This is thus analogous to the well known aldol condensation in solution, in which the initial aldol adduct loses water to yield crotonaldehyde. The possibility of a common mechanism for the gas phase and solution reactions is discussed.
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    The loss of SO2H from an imido-sulfite under electron impact: Structural elucidation by collision activation of the resulting fragment (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 405-409 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Electron impact mass spectrometry of an imido-sulfite 5,6-benzo-2-imino-N-(2,4,6-trichlorophenyl)-1,3-dioxa-2-thiacycloheptane shows an intense fragment ion corresponding to the expulsion of SO2H from the molecular ion. A mechanism that requires a rearrangement of the molecular ion is proposed. Structural elucidation of the [M—SO2H]+ ion was obtained by recording its metastable ion and collisional activation spectra. Comparison of these spectra with similar spectra recorded from a precursor ion of known structure demonstrated that they were identical. Thus, the results support the proposed structure which derives from the expulsion of SO2H from the molecular ion of the compound 5,6-benzo-2-imino-N-(2,4,6-trichlorophenyl)-1,3-dioxa-2-thiacycloheptane.
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    Unimolecular ethyl loss from metastable 13C labelled [C5H10O]+· ions with the oxygen on the middle carbon: An example for incomplete energy randomization? (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 421-422 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The investigation of 13C labelled 3-pentanone cation radicals generated via isomerization of the corresponding [C5H10O]+· enol cation radicals demonstrates unambiguously that, in contrast to previous investigations, unimolecular ethyl loss from 13C labelled 3-pentanone cation radicals is preceded by complete energy randomization.
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  • 161
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    Effect of protonation exothermicity on the chemical ionization mass spectra of some alkylbenzenes (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 423-427 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The H2, N2/H2, CO2/H2, N2O/H2, CO/H2 and CH4 chemical ionization mass spectra of thirteen C8 to C11 alkylbenzenes are reported. Characteristic hydride and alkide ion abstraction reactions are observed with all reagent gases. The major fragmentation reactions of [MH]+ are olefin elimination to form a protonated arene and arene elimination to form an alkyl ion. From the effect of structure and protonation exothermicity it is concluded that rearrangement of primary alkyl groups to the more stable secondary or tertiary structure occurs prior to alkyl ion formation. A detailed fragmentation mechanism for protonated arenes is proposed. The ‘effective’ proton affinity of the methane-derived reagent system is estimated to be ∼556 kJ mol-1.
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    An electron impact study of HCN elimination from indole by use of 13C labelling (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 444-447 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The study of the loss of HCN from the molecular ions of [2-13C]indole and [3-13C]indole shows that, to a good approximation, only the two carbon atoms of the pentagonal ring are involved in this fragmentation process, contrary to the behaviour of the H atoms; the C-2 atom is eliminated predominantly, chiefly in the ion source (85-90%) and a little less in the metastable energy range (75-80%). The losses of 13CCH3· and C2H3· from the [M—H12CN]+· ions of the two compounds suggest the occurrence of different structures, providing evidence for several mechanisms of HCN elimination.
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    Comparison of the fragmentations and reactivities of positive and negative ions. Thiocarboxylate ionsAlso Part CXLI in the series [Electron Impact Studies]: for Part CXL, see Ref. 1. (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 451-453 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (1) Thiocarboxylate anions [RCOS]- formed by dissociative secondary electron capture are either stable or fragment to yield [R]-. (2) Thiocarboxylate cations [RCOS]+ formed by charge stripping from [RCOS]-, fragment to form [R]+, [COS]+. and [RCO]+ (not when R=CF3). (3) Aryl hydrogen scrambling is observed in the case of the thiobenzoate cation. Aliphatic hydrogen scrambling is not detected for the thiopropionate cation.
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    Translational energy released in decompositions of metastable ions: A simple criterion for distinction between steroid epimers by mass spectrometry (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 465-466 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Tab.
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    URL: http://dx.doi.org/10.1002/oms.1210161010
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    Aluminium gaskets for mass spectrometers (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 466-466 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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    Masthead (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981) 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210161101
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    Dimesitylboryl compounds. VII - mass spectrometric studies (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 467-468 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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    Mass spectra of heterocyclic compounds: VFor Part IV, see Ref. 1. - dihydro-1,3,5-dioxazines (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 495-498 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: N-Substituted dihydro-1,3,5-dioxazines show a general fragmentation pattern supported by metastable ions, exact mass measurements and deuterium labelling. There are two well-defined pathways: one is initiated by elimination of the N-substituent and the other by loss of a hydrogen atom from the heterocyclic ring.
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    Basic questions in mass spectrometry (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 469-482 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The unimolecular dissociation of ionized molecules seldom consists in a direct bond cleavage where the reaction coordinate can be adequately represented by a simple bond stretch. The coordinate which controls the progress of the reaction is not always the reaction coordinate (defined as the degree of freedom whose extension leads to spatial separation of the molecular fragments). The specificity of a dissociation mechanism in a polyatomic species is due to its inherently multidimensional character, i.e. it requires participation of several degrees of freedom. It often consists of a sequence of elementary steps and is therefore controlled by several bottlenecks. The complicated and multistep nature of the reaction mechanism results in a natural tendency towards energy randomization. Radiationless transition from the initial upper electronic states to the ground state of the ion is not always very fast with respect to dissociation. A unimolecular reaction should be seen as a flux in phase space through a critical surface. A transition state corresponds to a surface of least flux, i.e. to a bottleneck of the reaction. For a given elementary step, several may exist, whose positions may vary with energy. The nature of these transition states is not immediately obvious. For instance, they do not necessarily coincide with saddle points or with rotational barriers.
    Additional Material: 13 Ill.
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    Doubly charged methane molecular ions: Observed in charge stripping reactions and absent in electron impact ionization spectra (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 512-513 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/oms.1210161109
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    Masthead (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981) 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210161201
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    Mass spectral cycloreversion reactions of 2-chloro-3,6-diaryl-3,4-dihydro-1,3,2-oxazaphosphorin-2-oxidesN.C.L. Communication No. 2797. (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 515-518 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mass spectral fragmentation modes of various 2-chloro-3,6-diaryl-3,4-dihydro-1,3,2-oxazaphosphorin-2-oxides - a novel ring system - reveal cycloreversion by two pathways. Retro Diels-Alder reaction by a stepwise mechanism is prominent in this system. The relative abundances of the enone and dienophile ions depend on the nature of the substituent attached to the double bond in this ring. Another retro Diels-Alder fragmentation process, involving the loss of PO2Cl from the molecular ion, is preceded by a 1,3-allylic rearrangement and is the major fragmentation mode in the metastable time scale. Further fragmentation of the [M—PO2Cl]+ imine ion seems to occur from cyclic dihydroquinoline intermediates by substitution elimination steps.
    Additional Material: 1 Tab.
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    Factors affecting reactivity in ammonia chemical ionization mass spectrometry (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 527-533 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several factors affecting reactivity in ammonia chemical ionization mass spectrometry (NH3 CI) have been examined. These include the sample proton affinity, the preferred site of protonation and [NH4]+ attachment, and substituent effects. In general, compounds having proton affinities ≲787 kJ mol-1 do not yield analytically useful intensities of the [M·NH4]+ adduct ion. Substituted aromatic compounds in which the ring is the most basic site yield little (if any) [M·NH4]+ ion even if the proton affinity of the compound is greater than 787 kJ mol-1. On the other hand, some aromatic compounds in which the substituent is the most basic site yield relatively abundant adduct ions. The spectra of compounds possessing a good leaving group (X) exhibit only weak [M·NH4]+ ions, but intense [M·NH4 - HX]+ and [M - X]+ ions formed by substitution and elimination reactions. Electronic effects strongly influence these processes. Several examples are presented in which isomers are readily differentiated because of different reactivities under ammonia chemical ionization conditions.
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    Doubly charged benzene and isomeric dications. Fragmentation energetics and charge distributions calculated by MINDO/3 molecular orbital theory (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 523-526 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: MINDO/3 calculations for singlet and triplet doubly charged benzene [C6H6]2+ are in satisfactory agreement with the experimentally determined values of the vertical double ionization energy of benzene; calculations for straight chain isomeric structures are consistent with the observed kinetic energy release on fragmentation to [C5H3]+ and [CH3]+. Symmetrical doubly charged benzene ions relax to a less symmetrical cyclic structure having sufficient internal energy to fragment by ring opening and hydrogen transfer towards the ends of the carbon chain. Fragmentation of [CH3C4CH3]2+ to [CH3C4]+ and [CH3]+ is a relatively high energy process (A), whereas both (B): [CH3CHC3CH2]2+ to [CHC3CH2]+ and [CH3]+ and (C): [CH3CHCCHCCH]2+ to [CHCCHCCH]+ and [CH3]+ may be exothermic processes from doubly charged benzene. Furthermore, the calculated energy for the reverse of process (A) is less than the experimentally observed kinetic energy released, whereas larger energies for the reverse of processes B and C are predicted. Heats of formation of homologous series [HCn]+, [CH3Cn]+, [CH2Cn-2CH]+, [CH3Cn-2CH2]+ and [CH2=CHCn-3CH2]+ with 1 〈 n 〈 6 are calculated to aid prediction of the most stable products of fragmentation of doubly charged cations. The homologous series [CH2Cn-2CH]+ is relatively stable and may account for ready fragmentation of doubly charged ions to [CnH3]+; alternatively the symmetrical [C5H3]+ ion [CHCCHCCH]+ may be formed. Dicoordinate carbon chains appear to be important stabilizing features for both cations and dications.
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    The mass spectra of halogeno derivatives of quinoxaline (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 5-11 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mass spectra of seventeen different quinoxaline halogeno derivatives are reported. The fragmentation mechanism is discussed.
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    Chemical ionization desorption mass spectrometry of some quaternary ammonium salts (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 17-20 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ammonia chemical ionization desorption spectra of N,N-dimethyl quaternary ammonium iodides in addition to high protonated molecular ion [M + H]+ intensity, show signals for an ion radical composed of N-methyl abstracted salt cation and ammonia [C + NH3—CH3]+·. These ions corresponding to the cation +2 show increased importance in the chemical ionization mode, using the same reagent gas. The technique of chemical ionization desorption appears suitable for the analysis of salts, and thus for the determination of the molecular weight of both anion and cation.
    Additional Material: 3 Tab.
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    The computer processing and interpretation of mass spectral information. VFor Part IV, see Ref. 1. - generation of a table of isotopic spectra of structural fragments (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 21-22 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A package of dialogue programs intended for generation of isotopic spectra from specified elemental compositions containing any number of elements is described. Structural fragments (super-elements), once in the table, acquire the status of a separate chemical element. All operations with super-elements are analogous to those with polyisotopic elements of the periodic table. The user can modify the table at his discretion to suit his purpose. The table increases the flexibility of interactive data processing programs and thus the dialogue is made to approach the natural chemist's language. The programs written in FORTRAN IV are intended for a minicomputer with a core memory of about 24 K words.
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    The computer processing and interpretation of mass spectral information. VIIFor Part VI, see Ref. 1. - identification of ions in terms of structural symbols (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 26-28 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new version of the AELITA-F program for computation of a monoisotopic spectrum and identification of the ion composition as a collection of elements or as structural fragments is described. A technique is proposed for specifying a priori information on the compound in a ‘hybrid’ form which combines structural fragments of the molecule and individual chemical elements. This version permits the elimination of redundant information and reduces the requirements of computer resources. The program effectiveness is increased by reducing the number of ions to be generated. The format in which the mass spectral information is read out is more comprehensible to a chemist.
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    Site of protonation in the reaction of gaseous Brønsted acids with halobenzene derivativesTaken in part from the MSc. Thesis of W. G. Liauw, University of Toronto (1981). (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 388-392 
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    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The site of protonation in the reaction of gaseous Brønsted acids with chlorobenzene and fluorobenzene derivatives has been examined using deuterium labelling of chlorobenzene and deuterated reagent gases (D2 and N2/D2). In the protonation of chlorobenzene by [H3]+ ∼30% of the [MH—HCl]+ fragment ions arise from a chlorine-protonated species while ∼70% arise from a ring-protonated species in which complete hydrogen scrambling has occurred. In the reaction of [N2H]+ with chlorobenzene ∼75% of the fragment ions arise from the chlorine-protonated form with ∼25% arising from the ring-protonated form of [MH]+. By contrast fluorobenzene fragments almost entirely from the fluorine-protonated form. Similar results are obtained for dihalobenzenes. The mechanistic implications are discussed.
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    Gas phase equilibration of triphenyl cyclohexenyl and diphenyl cyclopentenyl benzyl cationsNCL Communication No. 2778. (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 400-402 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Evidence for the gas phase equilibration of triphenyl cyclohexenyl and diphenyl cyclopentenyl benzyl cations directly or through common intermediates has been obtained from chemical ionization/collisional activation and kinetic energy release data.
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    URL: http://dx.doi.org/10.1002/oms.1210160908
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  • 181
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    Kinetic and thermodynamic effects on intramolecular aromatic substitution in meta and para substituted benzalacetonesSee Ref. 1. (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 410-415 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: meta and para substituted benzalacetones lose the substituents after electron impact in a multi-step intramolecular aromatic substitution. The differences in the relative abundances of the benzopyrylium ions thus formed are not determined by the activation energies for the substituent losses but depend on a delicate balance between the thermodynamic stability of the intermediates involved and the rates of several H-shifts within the intermediates (kinetic stability). The consequences for the analytical utility of intramolecular aromatic substitution are discussed briefly.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/oms.1210160911
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  • 182
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    Gas phase ion/molecule reactions in laser desorption mass spectrometry (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 416-420 
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    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The desorption of neutrals, alkali ions and quasimolecular ions of sucrose was studied as function of substrate temperature in laser desorption mass spectrometry. These phenomena were also investigated in thermal desorption experiments. It was concluded that in these experiments gas phase cationization is the major ionization process.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/oms.1210160912
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  • 183
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    Masthead (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981) 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/oms.1210161001
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  • 184
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    Skeletal rearrangements on chemical ionization of dibenzyl ether and derivatives (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 428-440 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Protonated molecular ions of dibenzyl ether, formed by chemical ionization using hydrogen and isobutane as reagent gases, undergo skeletal rearrangements to lose water and formaldehyde, both in the ion source and the flight path. The rearrangements have been elucidated by deuterium labelling and chemical substitution. The water lost contains the reagent proton and an aromatic hydrogen atom, and the aromatic hydrogen atoms have been shown to be mobile prior to the reaction. It is proposed that the skeletal rearrangement for water loss is initiated by protonation on the ether oxygen atom, followed by benzyl migration. The formaldehyde lost contains benzylic hydrogen atoms exclusively, and it is proposed that the skeletal rearrangement is preceded by hydrogen rearrangement of an oxygen protonated molecular ion to a ring protonated molecular ion. Daughter ion structures are supported by comparisons of their collision induced dissociation spectra with those of isomeric ions prepared by alternative routes.
    Additional Material: 1 Ill.
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    URL: http://dx.doi.org/10.1002/oms.1210161003
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  • 185
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    The loss of ortho halogeno substituents from substituted thiobenzamide ionsSee Ref. 1. (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 448-450 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The loss of ortho substituents (CH3, Cl, Br, I) from molecular ions of substituted thiobenzamides has been investigated by determination of the critical energy and kinetic energy released during this process to obtain some further insight into the corresponding reaction of N,N-dimethylthiobenzamide ions. In contrast to the latter compounds the ortho methyl substituent is not eliminated from the molecular ions of o-methylthiobenzamide, but the loss of ortho halogeno substituents occurs with identical reaction characteristics in both series of compounds. It is concluded that the loss of halogeno substituents from molecular ions in both series corresponds to a direct substitution reaction via a 4-membered transition state.
    Additional Material: 4 Tab.
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    URL: http://dx.doi.org/10.1002/oms.1210161006
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  • 186
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    Charge stripping reactions of ions formed from methane, ammonia, water and hydrogen sulphide by protonation and by electron impact (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 454-458 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The minimum energy, Qmin, necessary to convert an ion m1+ to a doubly charged ion m12+ is obtained for 19 different ions from methane, ammonia, water and hydrogen sulphide by charge stripping using nitrogen collision gas. The ions studied include the [MH]+ ions formed by chemical ionization in a high pressure source. Stable m12+ ions could not be formed in the case of [NH4]+, [NH]+·, [H2O]+· and [OH]+. Even in these cases the value of Qmin could be estimated by studying the fragments formed from the unstable m2+ ions. In several cases, the energy required to form m12+ ions is less than the literature value for the ionization energy of m1+. This is discussed in terms of the possibility of the presence of excited states of m1+ in the present experiments.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/oms.1210161008
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  • 187
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    Fragmentation mechanisms of isoxazole (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 459-464 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Fragmentation pathways of isoxazole giving ions [C3H2ON]+, [C2H3N]+· and [C2H2N]+ are elucidated by means of metastable ion studies and thermodynamic properties. Rearrangement reactions are demonstrated to occur with H and HCO loss. Elimination of carbon monoxide leads to [C2H3N]+· ions whose reacting configuration is the same as for acetonitrile. All these results can be rationalized in terms of a prior isomerization of isoxazole involving ring opening and 1,2 H migration.
    Additional Material: 8 Tab.
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    URL: http://dx.doi.org/10.1002/oms.1210161009
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  • 188
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    Elimination of water from the molecular ion of cycloheptanol (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 483-489 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Under electron impact cycloheptanol decomposes by four fragmentation paths: (1) α-cleavage with subsequent losses of C1-C5 fragments, (2) elimination of water, (3) loss of the hydrogen atom from C-1 and (4) loss of the hydroxyl group. The mechanism of water elimination was investigated by means of deuterium labelling. 1,4-Elimination of water predominates in cycloheptanol, with the stereospecific cis-1,3-elimination also being operative. The loss of water is preceded by extensive exchange of the hydroxyl hydrogen with those of the ring. This is attributed to a very facile transannular interaction of the hydroxyl group with the C-3 to C-6 positions that are made accessible due to conformational properties of the 7-membered ring. A kinetic model is proposed, describing migrations of the ring hydrogen atoms.
    Additional Material: 3 Ill.
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    URL: http://dx.doi.org/10.1002/oms.1210161103
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  • 189
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    A new linked scan for reversed geometry mass spectrometers (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 490-494 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A new linked scan is described by which fragmentations occurring in the second field free region of a two sector instrument can be monitored. The scan can be used only if the first stage allows selection of ions according to their masses. The magnetic sector and electric sector are scanned in unison so that the product B2E is maintained constant. A spectrum of all parents of a preselected daughter ion is obtained and the resolution depends only on the mass resolution of the magnetic sector.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/oms.1210161104
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  • 190
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    Electron impact induced hydrogen migrations in organic molecules: IV - novel hydrogen transfers in alkyl o-methoxybenzoates (1981)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 16 (1981), S. 499-501 
    Details
    ISSN: 0030-493X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Simultaneous hydrogen transfers - one from the methoxy group and the other from the alkyl group - to both the oxygen atoms of the ester function result in the formation of a common ion at m/z 152 in the alkyl o-methoxybenzoates on electron impact. Expulsion of the formyl radical from this ion leads to a fragment resembling the protonated benzoic acid. Another novel feature in these compounds is the loss of H2O from the [M—R]+ ion which arises through an ortho effect during a secondary fragmentation process.
    Additional Material: 2 Tab.
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    URL: http://dx.doi.org/10.1002/oms.1210161106
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  • 191
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    Masthead (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 15 (1981) 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270150101
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  • 192
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    77Se, 13C and 1H NMR investigations on ortho-carbonyl benzeneselenenyl derivatives (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 15 (1981), S. 152-154 
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    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: o-Carbonyl benzeneselenenyl compounds with COCH3, CHO and COOCH3 as carbonyl functions and SeCl, SeBr, SeSCN, SeSeCN, SeCN and SeCH3 as selenium-containing groups, have been studied by 1H, 13C and 77Se NMR spectroscopy. The IR C=O stretching frequencies of these compounds are also reported. If the SeCH3 derivatives are excluded, the compounds mainly adopt a planar ‘cis’ conformation, due to an interaction between the C=O group and the selenium atom. The range of over 800 ppm for the observed 77Se chemical shifts makes 77Se NMR spectroscopy a powerful tool for physical organic chemists.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/mrc.1270150208
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  • 193
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    15N NMR spectroscopy. 30For Part 29, see H. R. Kricheldorf, Polym. Bull. in press. - structure/shift relationships of oligopeptides and copolypeptides, including gramicidin S (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 15 (1981), S. 162-177 
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    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 15N NMR spectra of various oligopeptide derivatives of the Z—X—Y—Y—OMe structure, where X and Y are variable amino acids and Z is the benzyloxycarbonyl group, were measured in several protic and aprotic solvents. The shift difference of the 15N of the Y—Y and X—Y bond (neighbouring residue effect) is discussed with respect to the nature of X and Y with respect to the solvent. Oligopeptides of the Z—X—Y—Y—OH and n̊H3—X—Y—Y—OMe structures were compared with the Z-pëptide esters to investigate the spectroscopic influence of the protecting groups. The methyl ester hydrochlorides of the 25 most common amino acids were measured in water and DMSO to elucidate the solvent dependence of the substituent effects. Moreover, the methyl ester hydrochlorides were compared with Z-amino acids and N-acetyl-amino acid methyl esters in DMSO to establish whether the substituent effects depend on the nature of the amino acid derivatives. In this connection the assignments of the serine, threonine and glycine signals are discussed with respect to silk proteins. Furthermore, the assignments of the signals of copolypeptides by comparison with oligo- and homo-polypeptides are discussed. Finally, it was demonstrated that intramolecular H bonds cause downfied shifts of 7-10 ppm of the acceptor amide groups.
    Additional Material: 4 Ill.
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    URL: http://dx.doi.org/10.1002/mrc.1270150211
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  • 194
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    Fast searching for identical 13C NMR spectra via inverted filesDedicated to Dr W. Brügel on the occasion of his 65th birthday. (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 15 (1981), S. 178-187 
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    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Inverted files of spectral features should be employed when searching for identical or similar spectra. The efficiency of interescting the entries for chemical shifts with a small deviation is very high for larger molecules and incomplete spectra. A novel spectral code describing the spectral appearance in hierarchical order (SAHO) facilitates the search for complete spectra with a relatively high tolerance of the chemical shifts. A vailable information on the chemical composition of the molecule, as well as the incusion of SFOR-multiplicities, will further narrow down the number of suitable reference compounds.
    Additional Material: 8 Ill.
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    URL: http://dx.doi.org/10.1002/mrc.1270150212
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  • 195
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    1H and 13C nuclear magnetic resonance study of (D3)-trishomocuban-4-ol and (D3)-trishomocubanone (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 15 (1981), S. 188-192 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The complete assignments of the 1H and 13C NMR spectra for (D3)-trishomocuban-4-ol (3) and (D3)-trishomocubanone (4) are reported. The difference between the 1H and 13C chemical shifts of 3 and 4 and those of the hydrocarbon (D3)-trishomocubane, and the substituent effect of the hydroxy group, can be adequately explained by the unique stereochemistry of these compounds.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/mrc.1270150213
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  • 196
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    Diastereomeric non-equivalence of (-)-ω-camphanic esters of chiral secondary alcohols in 13C NMR spectroscopy (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 15 (1981), S. 193-196 
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    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The diastereomeric differences (Δδ) were measured by 13C NMR spectroscopy for a series of 11 (-)-ω-camphanic esters of secondary alcohols of known absolute configuration. This method cannot be used for the determination of the absolute configuration, but it can be applied to the estimation of the enantiomeric purity of chiral alcohols.
    Additional Material: 3 Tab.
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    Carbon-13 chemical shift assignments of the nitration products of pyrene (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 15 (1981), S. 197-199 
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    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 13C and 1H nuclear magnetic resonance (NMR) spectra have been obtained in order to identify the six nitration products of pyrene - 1-nitropyrene, 1,3-dinitropyrene, 1,6-dinitropyrene, 1,8-dinitropyrene, 1,3,6-trinitropyrene and 1,3,6,8-tetranitropyrene. 13C chemical shifts in DMSO-d6 were assigned using empirical rules, with particular emphasis on the additivity of the substituent effects. Carbon spectra of separated dinitromixtures enabled identification of the previously unreported 1,3-isomer, and proton spectra differentiated the 1,6- and 1,8- isomers.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/mrc.1270150215
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  • 198
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    1H NMR studies on dimeric 2-methylchromones (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 15 (1981), S. 208-210 
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    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A study is presented on the configuration and conformation of 2-methylchromone-dimer, as well as on khellin-dimer, based on 1H NMR spectroscopy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/mrc.1270150218
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    The nuclear magnetic resonance spectra of N-nitroso-N-alkyl amino acids (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 15 (1981), S. 200-204 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Structurally related acyclic and cyclic N-nitroso-N-alkyl amino acids were prepared and their 1H, 13C and 15N NMR spectra were investigated. The changes in the 13C NMR spectra of the N-nitroso α-amino acids after dissolving in solvents suggest that they posses the Z-configuration in the crystalline state; in solution some of them isomerize to mixtures of the Z- and E-isomers whose composition appear to depend on steric factors. The 13C chemical shifts were assigned on the basis of anisotropic effects of the nitrosamino group and configurational stability. The 13C chemical shifts were correlated with those of the nitrosamines of the same carbon skeletons and the effects of changing a methyl group to the carboxylic acid are deshielding on the α-carbons and shielding on the β-carbons.
    Additional Material: 7 Tab.
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    URL: http://dx.doi.org/10.1002/mrc.1270150216
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  • 200
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    A carbon-13 NMR study of phenyl-substituted cyclophosphazenes (1981)
    Chichester : Wiley-Blackwell
    Organic Magnetic Resonance 15 (1981), S. 205-207 
    Details
    ISSN: 0030-4921
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The 13C NMR spectra of the cyclotriphosphazenes N3P3CI6-n Phn (n=2, 3, 4, 6) and the tetrameric derivatives 2,2,6,6-N4P4CI4Ph4 and N4P4Ph8 have been recorded. The carbon chemical shifts can be largely explained on the basis of concomitant mesomeric electron release from the benzene ring and inductive electron withdrawal by phosphorus. The magnitude of 1J(P, C-1) for the non-geminal compounds is ≃40 Hz higher than that observed for the geminal compounds. Some aspects of the NMR data are also discussed with reference to the X-ray crystal structures of several phenyl-substituted cyclotri- and cyclotetra-phosphazenes.
    Additional Material: 2 Ill.
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    URL: http://dx.doi.org/10.1002/mrc.1270150217
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