SEMIEMPIRICAL CALCULATION AND NORMAL-COORDINATE STUDY OF THE CONFORMATION AND ELECTRONIC AND VIBRATIONAL-SPECTRA OF ACROLEIN

Detailed quantum chemical and normal coordinate calculations have been conducted on acrolein and its deutero derivatives to understand the s tructural and spectroscopic characteristics of its rotational isomers, in particular the cis isomer. The results of molecular orbital studie s in the MNDO (using the modified AM1 Hamiltonian), CS-INDO and CNDO a pproximations on potential energy curves, rotational barrier heights, conformations and physico-chemical properties of the ground and first excited (n pi) electronic states of acrolein are reported. Using mult ielectron configuration interaction based on the subroutine CIPSI, the electronic transitions have been explained. Generalized valence force fields have been obtained for the trans and cis conformers of acrolei n and their monodeutero derivatives. A complete assignment of the in-p lane and out-of-plane vibrational modes has been provided. II is infer red that while in the ground state the trans conformer of acrolein is more stable than the cis conformer, the reverse is the case in the fir st excited electronic state. In addition, a gauche conformer (phi = 90 degrees) may also exist in the excited state. (C) 1997 Elsevier Scien ce B.V.