TY - JOUR
T1 - On the bond-stretch isomerism in the benzo[1,2:4,5]dicyclobutadiene system - An ab initio MR-AQCC study
AU - Antol, Ivana
AU - Eckert-Maksić, Mirjana
AU - Lischka, Hans
AU - Maksić, Zvonimir B.
PY - 2004/7/19
Y1 - 2004/7/19
N2 - Bond-stretch isomerism in benzo[1,2:4,5]dicyclobutadiene (BDCB) has been investigated using the MR-AQCC/6-31G(d) method, a high-level multireference ab initio approach including size-extensivity corrections. The applied theoretical approach includes both nondynamical and dynamical electron correlation effects. Full MR-AQCC geometry optimizations of localized (1) and delocalized (3) isomers as well as the transition structure (TS) have been determined using D 2h symmetry restriction. The calculations show that both isomers are approximately of equal stability separated by a barrier with a height of about 5 kcalmol-1. Thus, the present results strongly indicate that benzo[1,3:4,5]dicyclobutadiene is a very good candidate for an organic compound exhibiting bond-stretch isomerism, since isomers 1 and 3 correspond to true minima on the double-well potential energy surface, which are separated by a sufficiently high barrier. It is particularly important to emphasize that isomer 3 represents a realization of the highly elusive quasi-[10]annulene.
AB - Bond-stretch isomerism in benzo[1,2:4,5]dicyclobutadiene (BDCB) has been investigated using the MR-AQCC/6-31G(d) method, a high-level multireference ab initio approach including size-extensivity corrections. The applied theoretical approach includes both nondynamical and dynamical electron correlation effects. Full MR-AQCC geometry optimizations of localized (1) and delocalized (3) isomers as well as the transition structure (TS) have been determined using D 2h symmetry restriction. The calculations show that both isomers are approximately of equal stability separated by a barrier with a height of about 5 kcalmol-1. Thus, the present results strongly indicate that benzo[1,3:4,5]dicyclobutadiene is a very good candidate for an organic compound exhibiting bond-stretch isomerism, since isomers 1 and 3 correspond to true minima on the double-well potential energy surface, which are separated by a sufficiently high barrier. It is particularly important to emphasize that isomer 3 represents a realization of the highly elusive quasi-[10]annulene.
KW - Ab initio calculations
KW - Aromaticity
KW - Carbocycles
KW - Fused ring systems
KW - Isomerization
UR - http://www.scopus.com/inward/record.url?scp=3442884262&partnerID=8YFLogxK
U2 - 10.1002/cphc.200301016
DO - 10.1002/cphc.200301016
M3 - Article
C2 - 15298383
AN - SCOPUS:3442884262
SN - 1439-4235
VL - 5
SP - 975
EP - 981
JO - ChemPhysChem
JF - ChemPhysChem
IS - 7
ER -