Title: Calculation of average values for CC bond lengths and CCC bond angles. PCILO conformational study of n-butane with the newly found and other molecular geometries
Abstract: The best average values for CC bond lengths and CCC bond angles were calculated for fragments in which the CC bond was at least one CC bond distant from heavy atom substituents by using the results of searches of the Cambridge Structural Database. The values found, 1.51 Å and 113° for a CCCH3 fragment, and 1.52 Å and 114° for a fragment inside a carbon chain, differ significantly from the values commonly used in theoretical calculations which are generally based on a limited set of crystallographic data or on the diamond structure. To test the sensitivity of quantum-chemical energy calculation methods to different input geometries, the PCILO method was taken as an example and checked for reproducibility of experimental conformational energy for the n-butane molecule. Energy minimization with respect to the CC bond length and the CCC bond angle led to values of 1.49 Å and 115°, respectively. For this geometry the gauche conformation was found to be preferred by 1.4 kJ mol−1 over the trans conformation. This result is inconsistent with experimental data and indicates that the proper choice of geometrical parametrization is of the greatest importance in energy calculations.
Publication Year: 1986
Publication Date: 1986-05-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 6
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