Double rotation mechanism, cyclopropane

At any rate, by 1984 the kinetic study of l,2-d2-cyclopropanes reported in 1975276 278 became the only unchallenged claim of kinetically favored two-center epimerization and of a predominance of the theoretically predicted double rotation mechanism . 

Interest in the decomposition of cyclopropanes and the role of the trimethylene biradical in the decay mechanism has spanned more than three decades and has been fueled by two experiments that give apparently irreconcilable results. Experiments of S,S-trans-cyclopropane-l,2-d2 at 695 K indicate that isomerization via double-terminal rotation (i.e., con- and disro-tation of the terminal methylene groups) is at least 6 times more prevalent than isomerization via single-terminal rotation. Similar experiments with chiral... 

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