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  • Basicity  (4)
  • Butanolides  (2)
  • Permethylation  (2)
  • 1
    Electronic Resource
    Electronic Resource
    Cyclopropan-Derivate, 2. Selbst-Acylierung der α-Alkyl-γ-lactone zu Herstellung von Bis(1-alkylcyclopropyl)ketonen über Spiro[4.4]acetale (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 2161-2166 
    Details
    ISSN: 0009-2940
    Keywords: Acetals ; Ketones ; γ-Lactones ; Butanolides ; Spiro compounds ; Cyclopropyl compounds ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyclopropane Derivatives, 2.  -  Self-Acylation of α-Alkyl-γ-lactones To Give Bis(1-alkylcyclopropyl)ketones via Spiro[4.4]acetalsHigh-yield synthetic ways are recommended for the title lactones 1.The coupling of two 2-alkyl-4-butanolides is possible in an inter-(1b, c) or intramolecular fashion (4c) to give spiro[4.4] acetals 8 or 9 respectively, in the absence of hindering substituents. Symmetrically substituted bis(1-alkylcyclopropyl)ketones 12 and 13 may be prepared by acidic cleavage of those spiro[4.4] acetals lacking 2,7-substituent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19901231112
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  • 2
    Electronic Resource
    Electronic Resource
    (E,Z)-Gleichgewichte, 15. Synthesen und erhöhte Konfigurationslabilität von 2-Iminoindan-Derivaten mit Vorderseitenspannung (1992)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 125 (1992), S. 2041-2049 
    Details
    ISSN: 0009-2940
    Keywords: Basicity ; Diastereotopomerization, (E/Z) ; Imines ; Steric shielding ; Steric strain ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: (E,Z) Equilibria, 15[1]. - Syntheses and Lability of the Configuration of 2-Iminoindan Derivatives with Front StrainSyntheses and properties are described for sterically shielded imines R2C = NR (3c, e, g-k), which are rather inert toward nucleophiles. Nucleophilic attack at the nitrogen atom of 3k is indicated by the formation of the azine 4. (E,Z) Configurational diastereotopomerization (anti/syn) is strongly dependent on N substituents [CH3, phenyl, 1-naphthyl, acetyl, Si(CH3)3, cyano, SC6H5, SOC6H5, SO2C6H5, and nitro]. It is accelerated by front strain along the C—N bond in 3a-c, e, g, h, j, and k and provides an energetic basis (by ΔG≠ and ΔΔG≠ values) for the gauging of force-field parameters. This (E,Z) stereo-mutation is characterized by a vanishing solvent dependence and a positive volume of activation (+10.2 cm3 mol-1 for 3a). In contrast to other π acceptor substituents, the N-nitro group in 31 retards (E,Z) interconversion.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19921250912
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  • 3
    Electronic Resource
    Electronic Resource
    (E, Z)1-Equilibria, 17 Demonstration of the Nitrogen Inversion Mechanism of Imines in a Schiff Base ModelDedicated to Professor Heinrich Nöth on the occasion of his 65th birthday. (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 747-754 
    Details
    ISSN: 0009-2940
    Keywords: Diastereotopomerization, (E, Z) ; Imines ; Inversion, nitrogen ; Permethylation ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Experimental differentiation between pure C=N double bond rotation and nitrogen inversion in N1-arylimines is possible with a single compound (13b) under the proviso of slow rotation about the N-aryl single bond. Labelling by 1H and 13C nuclei at the diastereotopic faces of the C=N moiety as well as of the N-aryl group is the clue to a successful stereodynamic analysis, as performed by variable-temperature NMR spectroscopy of 13b, a sterically congested and chiral model compound. Interpretation of similar measurements on a second model (13d) is less straightforward. The experimental observation of time-averaged Cs symmetry by NMR coalescences is only compatible with a mechanism of (E/Z) stereomutation either by pure inversion at sp2 nitrogen or by a contribution from C=N rotation together with a synchronized (geared) controtation about the N-aryl single bond. However, the latter combination is concluded to be predominantly inversion-like by comparisons with related imines.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931260327
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  • 4
    Electronic Resource
    Electronic Resource
    (E/Z) Equilibria, 16. Lone Electron Pair Donor Quality of the Imino Function: Synthesis and Reactivity of Sterically Strongly Congested Iminocyclopentanes (1993)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 126 (1993), S. 211-215 
    Details
    ISSN: 0009-2940
    Keywords: Imines ; Permethylation ; Substitution, electrophilic aromatic ; Steric shielding ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 2,6-Dimethyl-N-(2,2,5,5-tetramethylcyclopentylidene)aniline (4h) is obtained by permethylation; it forms salts (5) by N-protonation. Its CN double bond is strongly shielded against nucleophilic attack and cannot be hydrolyzed. Nitration and bromination occur smoothly in the aromatic p-position (12, 13), showing the directing power of the lone electron pair of the imino function. This π-donor quality is assessed by probing weaker electrophiles and by qualitative competition experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19931260129
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  • 5
    Electronic Resource
    Electronic Resource
    Cyclopropan-Derivate, 3. (1-Alkylcyclopropyl)ketone durch Acylierung von α-substituierten γ-Lactonen (1990)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 123 (1990), S. 2167-2172 
    Details
    ISSN: 0009-2940
    Keywords: Acylation ; Ketones ; γ-Lactones ; Butanolides ; Cyclopropyl compounds ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Cyclopropane Derivatives, 3.  -  (1-Alkylcyclopropyl)ketones by Acylation of α-Substituted γ-LactonesThe 2-acylation of 2-substituted 4-butanolides 2 is moderately sensitive to steric crowding, whereas the subsequent ring- opening of 2-acyl-2-alkyl-4-butanolides 4, 11 to give-chloro ketones 6, 12 by chloride-transferring acid derivatives be-comes difficult with bigger lactone substituents. Similar observations pertain to the preparation of y-chlorobutanoyl chlorides 10 from 2-alkyl-4-butanolides 2. The proper choice of the starting 4-butanolides (2a, b or 14 but not 2c) provides for an indirect coupling of two different lactones to y,y-dichloro ke-tones 12. Dicyclopropyl ketones 13 with variable patterns of substitution may thus be prepared from 4-butanolides in a direct manner with global yields exceeding 50% and without purification of intermediate products (except for acid chlorides like 10).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19901231113
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  • 6
    Electronic Resource
    Electronic Resource
    Sterically congested molecules, 15. Estimation of the ion-pair NH-acidity constant of the imino function (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 427-428 
    Details
    ISSN: 0947-3440
    Keywords: Acidity ; Basicity ; Imines ; Lithium imide ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The lithium imide 3 is slightly more basic than lithium bis(tri-methylsilyl)amide (5c) in THF solution. Based on a reported pKa value for hexamethyldisilazane (4c) and assuming the simplest form of ion-pair equilibration in eq. 1, the apparent pKa = 26.5 was determined for the imine 6.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199519950252
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  • 7
    Electronic Resource
    Electronic Resource
    Sterically congested molecules, 14. Imine protonation in toluene solution: A problem akin to the N-protonation in rhodopsin (1995)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1995 (1995), S. 419-425 
    Details
    ISSN: 0947-3440
    Keywords: Basicity ; Imine protonation ; Solvent effect ; Steric shielding ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The protonation state of N-(1,1,3,3-tetramethyl-2-indanylidene)methylamine (5/6) is assessed on the basis of fully assigned 1H- and 13C-NMR spectra in [D8]toluene and in CDCl3. In either solvent the basicity of 5 remains intermediate between those of pyridine (weaker) and triethylamine (stronger). Nearly complete proton transfer to 5 in toluene occurs with trifluoroacetic and dichloroacetic acids, whereas partial protonation is achieved by chloroacetic acid or acetic acid and even by biphenyl-2,2′-diol (7). As a possible model for imine protonation in the hydrophobic region of proteins like the rhodopsins, the sterically shielded iminium cation 6 (or 2) does not require solvation by a polar solvent; rather it can be stabilized in toluene solution by a counteranion whose proton affinity is diminished by an assisting hydrogen bond.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199519950251
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  • 8
    Electronic Resource
    Electronic Resource
    Sterically Congested Molecules, 12. Acidity Constants of Sterically Shielded Protonated Imines in Hydroxylic Solvents (1994)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1994 (1994), S. 943-948 
    Details
    ISSN: 0170-2041
    Keywords: Acidity constants ; Basicity ; Imines ; Solvation ; Steric shielding ; Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: NMR spectra in combination with pH measurements are shown to provide a simple and convenient procedure for determining the basicities of imines which are either slowly hydrolyzed (4, 5) or completely stable but inconveniently weak bases (11-13). The method has the advantage that it does not require any precise knowledge of the concentrations of the substrates or reagents. N-Alkyl (4, 15) and N-unsubstituted imines (5, 8, 9, 14) show quite similar basicities with a weak solvent dependence (from pure water to 99.5% methanol) which is akin to that of pyridine. The N-aryl imines 10-13 are less basic by ca. 4 pK units. It is concluded that spatial solvent exclusion by bulky substituents has remarkably little effect on the pKa′ values.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jlac.199419940916
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