Light- and heavy-atom tunneling in rearrangement reactions of cyclopropylcarbenes.

We investigated both light- and heavy-atom tunneling in the rearrangements of a series of cyclopropylcarbenes using canonical variational transition state theory with multidimensional tunneling corrections (CVT/MT) and the Wentzel-Kramers-Brillouin (WKB) formalism. Halogeno- and hydroxy-substituted cyclopropylcarbenes were found not to undergo carbon tunneling owing to wide reaction barriers. However, while carbon tunneling plays a major role in the ring expansion of parent cyclopropylcarbene yielding cyclobutene, cyclopropylmethylcarbene is prone to undergo hydrogen tunneling to give cyclopropylmethylene.