Reactivity in the Addition-Elimination Route

Since bond making is assumed to be the rate-determining step, it is expected that the relative reactivities of different activated olefins will be similar to those found in other nucleophilic reactions (e.g., additions) 

Introduction of an o-nitro group into the mildly reactive cis and trans-/8-bromo-p-nitrostyrenes increases the rate with PhS ion 3400 and 41,500 

Kate Constants and Activation Parameters in the Addition-Elimination Koute 

C1CH=CHCN Piperidine MeOH 200 267 Scotti and Frazza, 1964 

The introduction of an a-chlorine as a second activating group into jS-chloro-a-phenylsulphonylethylene has only small effect on the reactivity. With MeO- ion the rate increases 2-3- to 3-8-fold, and with PhS- ion 4- to 21-fold. The relative activating ability of the halogens was discussed in Section (IIIB,3). 

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