Thermal Aromatizations
of 2-Vinylmethylenecyclopropane
and 3-Vinylcyclobutene
- Publication date
- Publisher
Abstract
A comprehensive theoretical investigation of thermal
rearrangements
of 2-vinylmethylenecyclopropane and 3-vinylcyclobutene is carried
out employing density functional theory and high level ab initio methods,
such as the complete active space self-consistent field, multi-reference
second-order Møller–Plesset perturbation theory, and coupled-cluster
singles and doubles with perturbative triples. In all computations,
Pople’s polarized triple-ζ split valence basis set, 6-311G(d,p),
is utilized. The potential energy surface for the relevant system
is explored to provide theoretical insights for the thermal aromatizations
of 2-vinylmethylenecyclopropane and 3-vinylcyclobutene. The rate constant
for each isomerization reaction is computed using the transition state
theory. The simultaneous first-order ordinary-differential equations
are solved numerically for the considered system to obtain time-dependent
concentrations, hence the product distributions at a given temperature.
Our results demonstrate that at high temperatures thermal aromatizations
of 2-vinylmethylenecyclopropane (at 700 °C and higher) and 3-vinylcyclobutene
(at 500 °C and higher) are feasible under appropriate experimental
conditions. However, at low temperatures (at 500 °C and lower),
2-vinylmethylenecyclopropane yields 3-methylenecyclopentene as a unique
product, kinetically, and the formation of benzene is not favorable.
Similarly, at 300 °C and lower temperatures, 3-vinylcyclobutene
can only yield <i>trans</i>-1,3,5-hexatriene (major) and <i>cis</i>-1,3,5-hexatriene (minor). At 300 < <i>T</i> < 500 °C, 3-vinylcyclobutene almost completely yields 1,3-cyclohexadiene.
Hence, our computations provide a useful insight for the synthesis
of substituted aromatic compounds. Further, calculated energy values
(reaction energies and activation parameters) are in satisfactory
agreement with the available experimental results