A scaled ab initio HF/6-31G force field has been optimized that provides an
accurate description of normal mode frequencies and eigenvectors of branch
ed alkanes. This force field reproduces 159 observed non-CH stretch bands o
f 10 conformers of 2-methylpropane, 2,2-dimethylpropane, 2-methylbutane, 2,
2-dimethylbutane, and 3-methylpentane with an rms deviation of 6.1 cm(-1).
A number of modes have been reassigned based on this vibrational analysis.
The force field serves as the basis for the development of a spectroscopica
lly accurate molecular mechanics energy function for saturated hydrocarbon
chains. (C) 2000 Elsevier Science B.V. All rights reserved.