Abstract
The competitive elimination (E2) and substitution (SN2) reactions of cyclohexyl tosylate with Triphenylphosphine are examined. Triphenylphosphine is taken to be representative of neutral weak bases which have good nucleophilic affinity for carbon. But it is a poor reagent for elimination when compared with anionic weak bases which are also good carbon nucleophiles. The stronger neutral bases triethylamine and 1,5-diazabicyclo[4.3.0]non-5-ene (DBN) are more effective than the anions in inducing elimination. It is concluded that whilst an interaction between the base and Cα is an important structural component of the E2C transition state, the interaction is primarily electrostatic rather than covalent (SN2-like) as has been previously supposed. The reaction of Ph3P with cyclohexyl bromide, a more E2H-like substrate, is almost completely substitution, indicating that neutral weak bases are also ineffective when more E2H-like transition states are involved, as is to be expected.
Published Version
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