Abstract:
The rates of bimolecular substitution and elimination reactions depend on the nucleophilicity of the reagent, which is its affinity for atomic nuclei in general. It has been common practice to draw a parallel between the nucleophilic character of the reagent and its basicity; strong bases are regarded as strong nucleophilic reagents and weak bases are regarded as weak nucleophiles. But the strength of a base is its affinity for a hydrogen atom
whereas the nucleophilicity of a reagent in nucleophilic substitutions is its affinity for electron deficient centres on carbon atoms
The parallelism between nucleophilic power and basicity is therefore not expected to hold in bimolecular substitution reactions although it may succeed in correlating the relative activity of the nucleophiles in bimolecular elimination reactions where the attack is on a hydrogen atom.