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Natural steric analysis of internal rotation barriers
Author(s) -
Badenhoop J. K.,
Weinhold F.
Publication year - 1999
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/(sici)1097-461x(1999)72:4<269::aid-qua9>3.0.co;2-8
Subject(s) - steric effects , chemistry , van der waals force , natural bond orbital , computational chemistry , molecule , butane , van der waals radius , chemical physics , stereochemistry , density functional theory , organic chemistry , catalysis
We apply natural bond orbital (NBO) steric analysis (introduced in a previous article) to obtain the steric exchange contribution to the internal rotation barriers of butane, ethane, and other related molecules (CH 3 NH 2 , CH 3 OH, NH 2 OH). The expected exchange repulsion between the two methyl group CH bonds within van der Waals contact in butane is shown to be the major contributor to the syn barrier and provides a method for calculating allowed ranges of torsional angles in macromolecules. However, the exchange‐energy difference between the staggered and eclipsed forms predict a counterintuitive eclipsed minimum for ethane, methylamine, and methanol. We show that the full SCF barrier in such apolar molecules can be reasonably approximated as a sum of this steric term plus the hyperconjugative terms as previously evaluated. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 72: 269–280, 1999