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IR and computational studies of alkyl chloride conformations
Author(s) -
Kingsbury Charles A.,
Lee KyungHoon
Publication year - 2000
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/1099-1395(200005)13:5<244::aid-poc237>3.0.co;2-e
Subject(s) - chemistry , alkyl , antibonding molecular orbital , conformational isomerism , infrared spectroscopy , infrared , chloride , crystallography , population , computational chemistry , atomic orbital , molecule , organic chemistry , physics , demography , quantum mechanics , sociology , optics , electron
Abstract ‘Natural bond orbitals’ population analysis calculations are used to explain the differences in infrared absorptions of alkyl chlorides conformers. Hydrogen anti to the C—Cl bond affords greater σ C—H → σ* C—Cl than does carbon anti to C—Cl, σ C—C → σ* C—Cl . Owing to the greater antibonding character in the former case, the C—Cl bond distance is generally larger, and the C—Cl infrared absorption of lower frequency. Attempts to quantify the use of intensities from infrared spectra to give the weight of the particular conformation of an alkyl chloride are reported. The difficulty is that the absorption coefficient α (cf. A A = α A C A ℓ ) is not known. The ratio α A /α B was approximated from intensities of infrared peaks of two conformations, A and B, as determined from various types of theoretical calculations. The ratio of absorbances A A / A B was determined from the spectra. Then, C A / C B was calculated and compared with the results from various types of pure calculation. In simple alkyl chlorides, this approach was modestly successful. Copyright © 2000 John Wiley & Sons, Ltd.