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Ab initio studies of structural features not easily amenable to experiment. 32. Conformational analysis and molecular structures of isopropyl and ethyl formate and comparison with spectroscopic data
Author(s) -
Klimkowski V. J.,
Schäfer Lothar,
Bohn Robert K.
Publication year - 1984
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.540050208
Subject(s) - isopropyl , conformational isomerism , formate , chemistry , ab initio , ethyl formate , computational chemistry , ab initio quantum chemistry methods , rotational spectroscopy , molecule , medicinal chemistry , organic chemistry , catalysis
The geometries of several conformations of ethyl and isopropyl formate were optimized by the ab initio gradient method on the 4‐21G level. The calculations are in agreemnt with the existence of two conformers of ethyl formate of nearly equal energy. The COCC torsional angle in one is anti (180°) and in the other is gauche (about 80°). The equilibrium configuration of the isopropyl group in the formate is found to be unsymmetrical, with a COCH torsional angle of about 40°. A second minimum of torsional energy, at COCH = 180°, is 1.2 kcal/mol less stable than the unsymmetrical form. The calculations demonstrate the tranferability of internal rotational‐potential parameters and of conformationally dependent geometrical trends between ethyl and isopropyl formate. There is good agreement between the calculated results and empirical potential‐energy functions and rotational constants determined from microwave spectroscopy.