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Theoretical investigation of the conrotatory ring opening of cyclobutene and 1, 2‐dihydro‐1, 2‐diazacyclobutadienes with ab initio and density functional Gaussian‐type‐orbital approach
Author(s) -
Jursic Branko S.,
Zdravkovski Zoran
Publication year - 1995
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.560560206
Subject(s) - conrotatory and disrotatory , cyclobutene , ab initio , ring (chemistry) , chemistry , computational chemistry , steric effects , density functional theory , basis set , ab initio quantum chemistry methods , molecule , stereochemistry , organic chemistry
The theoretical study of the thermally allowed conrotatory opening of cyclobutene (1) and cis ‐ (2) and trans ‐1,2‐dihydro‐1,2‐diazacyclobutadiene (3) were performed with ab initio and density functional calculations. The reactants and the transition states were fully optimized by using the 6‐31 + G** basis set with RHF , MP2 , SVWN , and BLYP methods. The calculated activation barriers for the ring opening of 1 with both MP2 and SVWN incorporating ZPVF correction give extraordinary agreement with the experimental value. The predicted activation energies for 2 and 3 are lower than in the case of the cyclobutene ring opening. Of the two 1,2‐dihydro‐1,2‐diazacyclobutadiene isomers, the trans isomer has a lower activation barrier. The structural and energy differences and the trend among these compounds are interpreted in terms of orbital overlap and steric interactions in the course of the conrotatory ring opening. © 1995 John Wiley & Sons, Inc.