Rearrangement of trans-1,2-divinylcyclobutane and the energy surface of the dimers of butadiene

Abstract

In many thermal reactions, the experimentally determined heat of formation (ΔH_f^0) of the transition state is that predicted by bond additivity data to be appropriate for a species with one broken bond, a "diradical."From the logical converse of this correspondence, a procedure has developed for estimation of ΔH_f^0 of a hypothetical diradical intermediate in a given reaction by measurement of the activation energy of a different reaction assumed to pass through the "same" intermediate. A recent important application has concerned the energy surface common to the dimers of butadiene, in which values of ΔH_f^0 for the hypothetical octa-1,7-diene-3,6-diyl diradicals *trans,trans*, *cis,-trans*, and *cis,cis* were estimated from various pyrolysis reactions (Scheme I) of trans- 1,2-divinylcyclobutane (1), 4-vinylcyclohexene (2), and cycloocta-1,5-diene (4).

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