Base- and solvent-catalysed eliminations

A number of examples of the ElcB mechanism has been reported (c/. Section 2.1.3).  

The theory of the variable transition state for base-catalysed E2 reactions has been reviewed and has been used to explain the Hammett reaction con-stants , kinetic isotope effects , and orientational features of some base-catalysed elimination reactions (c/. Section 2.2). 

The Brdnsted equation has been used to confirm concerted rather than stepwise base-catalysed eliminations - . However, parallel Brdnsted plots were found for primary, secondary, and tertiary amines. Bordwell et al. have reported values of the Brdnsted component, /3, which are greater than unity for the ionisation of psuedo acids, such as nitroalkanes, for which proton removal by a base is not diffusion-controlled . Values greater than unity are not to be 

An ion-pair mechanism has been proposed for the elimination of I-phenyl-ethyl bromide with ethoxide ion as the second-order rate coefficient decreases with increasing base concentration . However, this variation in rate can be attributed to association of the base in the more concentrated solution . 

Details of the theoretical calculations of isotope effects (both Ah/ d and for various model transition states in the elimination of 2-phenyl-ethyldimethylsulphonium ion have appeared (c/. Section 2.2.3). 

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