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Coupling of internal rotations in propanelike molecules
Author(s) -
Wesenberg G.,
Weinhold F.
Publication year - 1982
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.560210212
Subject(s) - chemistry , steric effects , atomic orbital , molecular geometry , eclipsed conformation , coupling (piping) , molecule , lone pair , methyl group , group (periodic table) , bond length , crystallography , computational chemistry , propane , rotation (mathematics) , molecular physics , stereochemistry , geometry , physics , materials science , quantum mechanics , organic chemistry , mathematics , metallurgy , electron
A linear‐combination‐of‐bond‐orbitals (LCBO) formulation of INDO–SCF–MO theory is employed to investigate the origin of rotation barrier coupling in propane and related molecules. The dominant contributions to rotor coupling in propane are identified to be (i) a direct steric (bond–bond) interaction, involving the close approach of two methyl CH bonds in the eclipsed–eclipsed geometry, and (ii) a nonvicinal bond–antibond effect, which arises when the side of a σ CH bond orbital in an eclipsed methyl group comes into favorable overlap with the “backside” lobe of the coplanar σ CH *antibond in the staggered–eclipsed geometry. A smaller nonadditive interaction of each methyl rotor with the central group is noted to be of importance when the central atom contains lone pairs. Aspects of this qualitative picture, and its dependence on geometry changes, are tested in applications to (CH 3 ) 2 CHF, (CH 3 ) 2 NH, (CH 3 ) 2 O, (CH 3 ) 2 CCH 2 , (CH 3 ) 2 CO, and C(CH 3 ) 4 .