Ab initio study of the 1,3-butadienyl radical isomers
C. L. Parker and A. L. Cooksy
Department of Chemistry, University of Mississippi,
University, MS 38677
Abstract
Ab initio calculations at the B3LYP, QCISD, and MCSCF levels of
theory and using the 6-311G(d,p) basis set were carried out on the
ground state of the 1,3-butadiene derived radicals. The
1,3-butadien-1-yl and 1,3-butadien-2-yl radicals are obtained from
1,3-butadiene by abstraction of a hydrogen atom from a primary and
secondary carbon, respectively. The 1,2- butadien-4-yl radical was
also studied to examine the possibility of the relocalization of the
unpaired electron from 1,3-butadien-2-yl. 1,2-butadien-4-yl was
consistently found to be the most stable isomer. The MCSCF relative
energies are 29 kJ mol-1 for 1,3-butadien-2-yl, and 35 kJ
mol-1 for the most stable of the 1,3-butadien-1-yl
configurational isomers. The 1,3-butadien- 2-yl structure is found to
be a local minimum in MCSCF calculations, but with an isomerization
barrier of less than 1 kJ mol-1, and deforms to the
1,2-butadien-4-yl isomer at all other levels of theory used. The
energy of the most stable 1,3-butadien-1-yl isomer relative to
1,3-butadien-2-yl ranges from 9 to 18 kJ mol-1 across all
levels of theory used, substantially lower than previous predictions by
ab initio and semi-empirical means. Optimized geometries, relative
energies, permanent dipole moments, Fermi contact terms and harmonic
vibrational frequencies are reported.