FREE-RADICAL ADDITION REACTIONS WITH CYCLIC OLEFINS . ROLE OF MEDIUM RING SIZE EFFECT

A study of free-radical addition reactions with cyclic olefins has demonstrated a marked difference in relative reactivity depending on whether the radical addition step is reversible or nonreversible. The reactivity of cyclic olefins with nonreversible addends, acetaldehyde, and bromotrichloromethane is not very sensitive to ring size, and it decreases in the order cyclooctene > cyclopentene > cycloheptene > cyclohexene. The order of reactivity with reversible addends, hydrogen bromide, and ethanethiol is nearly the opposite—cyclohexene > cyclopentene > cycloheptene ≫ cyclooctene—and the decrease with cyclooctene is 10- to 100-fold. This inverse behavior is attributed to the role of the “medium ring size” effect (also known as I strain) in the reversible additions. © 1969, American Chemical Society. All rights reserved.