Web Release Date: July 30,
Adjacent Gauche Stabilization in Linear Alkanes: Implications for Polymer Models and Conformational Analysis
and
Laboratory of Computational Biology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892-8014, and Laboratory of Biophysics, Center for Biologics Evaluation and Research, FDA, 1401 Rockville Pike, Rockville, Maryland 20852-1448
Received: May 25, 2005
In Final Form: June 29, 2005
Abstract:
High-level ab initio quantum mechanical calculations are used to study various gauche conformational energies of n-pentane to n-decane. The destabilizing "pentane effect" (adjacent gauche states of opposite sign) for alkanes is confirmed, but the energies were found to depend slightly on chain length. In contrast, introducing an adjacent gauche of the same sign requires only 0.22-0.37 kcal/mol, approximately half of the single gauche state energy. This adjacent gauche stabilization should be taken into account when formulating or analyzing rotational isomeric models, carrying out conformational analysis, and developing force fields for alkanes, lipids, and related polymers.
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