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Low-resolution microwave, infrared and Raman spectra, ab initio calculations and conformational analysis of 1-bromo-2-methoxyethane (1992)

Durig, J. R. ; Larsen, R. A. ; Sheehant, T. G. ; [et al.]

Springer

Structural chemistry 3 (1992), S. 253-268

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ISSN: 1572-9001

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology

Notes: Abstract The microwave spectrum of gaseous 1-bromo-2-methoxyethane, BrCH2CH2OCH3, has been recorded from 18.0 to 27.0 GHz at low resolution. The Raman spectra of the gas, liquid, and solid along with the infrared spectra of the gas and solid have been recorded from 3500 to 50 cm−1. A comparison of the vibrational spectra obtained for the fluid phases with those obtained for the annealed solid indicates the presence of more than one conformer in the fluid phases. The presence of two asymmetric rotors allows for five possible conformations, a majority of which are present in the gaseous phase. It is concluded that the conformation present in the solid phase is that of the gauche/trans (GT) form, where the first term refers to the carbon-bromine bond and the second term to the carbon-oxygen bond (methoxy group). In the gas phase the major absorption in the microwave spectrum is a result of the trans/trans (TT) form although it is certain that other conformations are also present. From a variable temperature study of the Raman spectrum of the liquid, the enthalpy difference between the conformers of the—OCH3 group was found to be 850 ±115 cm−1 (2.43±0.33 kcal/mol) whereas the difference between the conformers of the—CH2Br group as found to be 510±24cm−1 (1.46±0.07 kcal/mol). The conformational energy differences, vibrational frequencies, and structural parameters have been obtained from ab initio calculations with the STO-3G* basis set, and these theoretical values are compared to the experimental values. All of these results are compared to similar data for some corresponding molecules.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00672793

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Raman and infrared spectra, conformational stability and vibrational assignment for 1,1,1-trifluoro-2-methoxypropane (1990)

Durig, J. R. ; Larsen, R. A. ; Kelley, Rosalyn ; [et al.]

Chichester [u.a.] : Wiley-Blackwell

Journal of Raman Spectroscopy 21 (1990), S. 109-122

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ISSN: 0377-0486

Keywords: Chemistry ; Analytical Chemistry and Spectroscopy

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Physics

Notes: The Raman spectra of gaseous, liquid and solid 1, 1, 1-trifluoro-2-methoxypropane, CF3(CH3)CHOCH3, and the corresponding methoxy-d3 isotope, CF3(CH3)CHOCD3, together with the infrared spectra of the gases and solids were recorded from 3500 to 30 cm-1. A comparison of the vibrational spectra obtained for the fluid phases with those obtained for the amorphous and annealed solids indicates the predominance of two conformers in the fluid phases at ambient temperature. Owing to possible steric hindrance, it is suggested that the most stable conformer is the gauche-2 form, which has the methoxy group trans with respect to the carbon-carbon bond of the perfluoromethyl group. This conformer is the one present in the solid. The other conformer in appreciable abundance in the fluid states is probably the gauche-1 form, which has the methoxy group trans to the carbon-carbon bond of the methyl group. From a temperature study of the Raman spectrum of the liquid, the enthalpy difference between these conformers was determined to be 180 ± 100 cm-1 (515 ± 286 cal mol-1). The asymmetric torsional frequencies for the gauche-2 and gauche-1 conformers are 93 and 53 cm-1, respectively, and from these data and the enthalpy difference the values for the potential constants governing the internal rotation have been estimated. The normal modes have been assigned based on group frequencies, isotopic shifts, depolarization values and infrared band contours. The barrier to internal rotation of the methyl group is calculated to be 1275 cm-1 (3.65 kcal mol-1) from the torsional frequency of 234 cm-1 of the solid.

Additional Material: 7 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/jrs.1250210208

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