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Isotope substitution effects on preferred conformations of some hydrocarbon radical cations
Author(s) -
Lunell S.,
Eriksson L. A.
Publication year - 1992
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560440852
Subject(s) - cyclopropane , chemistry , kinetic isotope effect , butane , deuterium , computational chemistry , hydrocarbon , spectral line , photochemistry , ring (chemistry) , organic chemistry , atomic physics , physics , astronomy , catalysis
The stability of different conformational isomers of partially deuterated radical cations of ethane, butane, and cyclopropane is studied at the HF/6‐31G** and MP2/6‐31G** levels. It is shown that the superposition patterns of spectra corresponding to different isomers, observed in ESR spectroscopy, are accurately reproduced by Boltzmann statistics based on differences in vibrational zero‐point energies (ZPE), provided that the temperature is high enough to overcome existing barriers toward internal pseu‐dorotation in the cations. For the ethane and butane cations, the most stable conformations are, as expected, those which are deuterated in the short CH bonds, while this is found not to be the case for the cyclopropane cation. The latter result is explained by shifts in the low‐frequency bending modes, which counteract the anticipated isotope effect on the CH stretching modes. © 1992 John Wiley & Sons, Inc.