Balancing dynamic and nondynamic correlation for diradical and aromatic transition states: a renormalized coupled-cluster study of the cope rearrangement of 1,5-hexadiene.
Single-reference coupled-cluster calculations employing the completely renormalized CCSD(T) (CR-CCSD(T)) approach have been used to examine the mechanism of the Cope rearrangement of 1,5-hexadiene. In agreement with multireference perturbation theory, the CR-CCSD(T) method favors the concerted mechanism of the Cope rearrangement involving an aromatic transition state. The CCSD(T) approach, which is often regarded as the "gold standard" of electronic structure theory, seems to fail in this case, favoring pathways through diradical structures.
McGuire
Michael J
MJ
Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, USA.
Piecuch
Piotr
P