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Communications to the Editor Vinylic Cations from Solvolysis. XIX.1 Low
 

Summary: 2612
Communications to the Editor
Vinylic Cations from Solvolysis. XIX.1 Low
Tosylate-Bromide Reactivity Ratios in Vinylic
Solvolyses. Do koTs/kBrRatios Measure the Polarity
of the Solvolytic Transition State?
Sir:
A few years ago Hoffmanq2 following DePuy and
Bishop, suggested the ratio of the displacement rates of
tosylate and bromide leaving groups (kOTs/kBr)as a
mechanistic criterion for the extent of bond breaking in
the solvolysis transition state. Ratios <1 were found
mainly with primary substrates in reactions of nucleo-
philes which involve strong bond making. High
(>IO3) ratios were found for easily ionized, mostly
tertiary, substrates, and intermediate ratios characterize
secondary substrates. Large ratios were suggested to
indicate very ionic transition states and vice versa, and
solvation and steric factors were assumed to be less im-
portant than the charge dispersal effects. It was gen-

  

Source: Apeloig, Yitzhak - Department of Chemistry, Technion, Israel Institute of Technology

 

Collections: Chemistry