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Comparison of AM1 and ab initio calculation of the carbon‐carbon bond rotation in ethylene glycol diacetate
Author(s) -
Fagerburg David R.
Publication year - 1991
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.540120611
Subject(s) - dihedral angle , ab initio , ethylene glycol , chemistry , ethylene , bond length , computational chemistry , ab initio quantum chemistry methods , maxima and minima , molecular geometry , methylene , conformational isomerism , basis set , crystallography , molecule , density functional theory , organic chemistry , crystal structure , hydrogen bond , mathematics , mathematical analysis , catalysis
The C‐C glycol bond rotational energy in ethylene diacetate as a polyester model was compared using the semiempirical method AM1 and an ab initio method with an STO‐3G basis set. The results were qualitatively much different depending on the method used. Ab initio calculations showed the expected minima at 180 and near 60 (69.6) degrees dihedral angle with maxima at 0 and 120 degrees. The AM1 rotational curve indicated an apparent minimum at a 90 degree dihedral angle, a shallow, apparent maximum at 180 degrees and an apparent maximum at 0 degrees which could not be confirmed as minima or maxima via frequency calculations. Ethylene diacetate analog compounds with one or two ester oxygens replacing methylene group(s) gave curves with AM1 having the general shape for ethylene diacetate by the ab initio method, indicating a parameterization problem for the otherwise very useful AM1 to correctly handle a compound with only two carbons between the two electronegative oxygen atoms thus rendering this method currently unsuitable for examination of rotational energy barriers of such polyester model compounds.