Homolytic ring fission reactions of bicyclo[n.1.0]alkanes and bicyclo[n.1.0]alk-2-yl radicals: Electron spin resonance study of cycloalkenylmethyl radicals

Charles Roberts, John C. Walton*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

27 Citations (Scopus)

Abstract

Hydrogen abstraction from bicyclo[n.1.0]alkanes (n = 3-6) by t-butoxyl radicals was examined by an e.s.r. technique. The main site of attack was C(2) giving bicyclo[n.1.0]alk-2-yl radicals which rearranged by β-scission of the outer cyclopropane bonds to give cycloalkenylmethyl radicals. This is in contrast to the bicyclo[n.1.0]alk-2-yl radicals (n = 1, 2) which rearranged by fission of the inter-ring bonds to give cycloalkenyl radicals. β-Scission in bicyclo[n.1.0]alk-2-yl radicals was examined by semi-empirical SCF MO calculations. The conformations and barriers to internal rotation of the cycloalkenylmethyl radicals were determined from the variation in the β-H hyperfine splitting constants with temperature. Photo-bromination of bicyclo[n.1.0]alkanes (n = 3, 4) was also investigated in CCl4 solution. The main process was bimolecular homolytic substitution (S H2) by bromine atoms at the cyclopropane carbons, but there was an increase in hydrogen abstraction with ring size. The SH2 reactions parallel the β-scission reactions of the bicyclo[n.1.0]alk-2-yl radicals in that the main bond undergoing fission changes from the inter-ring bond to the outer cyclopropane bond as the ring size increases.

Original languageEnglish
Pages (from-to)879-885
Number of pages7
JournalJournal of the Chemical Society, Perkin Transactions 2
Issue number6
DOIs
Publication statusPublished - 1 Jan 1983

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