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On the applicability of the MINDO /3 method in studies of molecular structures in the vapor phase. Geometries, conformational energies, and vibrational amplitudes of alkenes and chloroalkanes
Author(s) -
Van Hemelrijk D.,
Versichel W.,
Van Alsenoy C.,
Geise H. J.
Publication year - 1981
Publication title -
journal of computational chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.907
H-Index - 188
eISSN - 1096-987X
pISSN - 0192-8651
DOI - 10.1002/jcc.540020112
Subject(s) - mindo , conformational isomerism , scaling , chemistry , computational chemistry , molecule , amplitude , force field (fiction) , electron diffraction , thermodynamics , diffraction , physics , quantum mechanics , mathematics , geometry , organic chemistry
The geometries and force fields of the different conformers of five alkenes and five chloroalkanes (17 conformers in total) were calculated in the MINDO /3 approximation and compared with the corresponding experimental values. The direct use of geometrical or vibrational parameters derived from MINDO /3 either as starting values or as a source of constraints in the analysis of gas‐phase electron diffraction data presents great risks. After a scaling procedure in which the calculated values are fitted to the experimental ones for a small number of compounds, scale factors can be obtained which, with due caution, are transferable to other molecules in the same class. Scaled MINDO /3 produces geometries and force fields that fit to experiment considerably better than their unscaled counterparts. However, scaled MINDO /3 does not produce better results than molecular mechanics. Calculated energy differences between rotamers are generally too high.