Definition of nucleophilicity

1. (1) The property of being nucleophilic.

   (2) The relative reactivity of a nucleophilic reagent. (It is also sometimes referred to as "nucleophilic power".) Qualitatively, the concept is related to Lewis basicity . However, whereas Lewis basicity is measured by relative equilibrium constants,

   B: + A B+-A- (equilibrium constant K)

   nucleophilicity of a Lewis base is measured by relative rate constants of different nucleophilic reagents towards a common substrate, most commonly involving formation of a bond to carbon,

   B: + A-Z B+-A- + Z:- (rate constant k)

   See also electrophilicity, Ritchie equation, Swain-Scott equation.

   n-* delocalization (or n-* no bond resonance)

   Delocalization of a free electron pair (n) into an antibonding -orbital (s*).

   See hyperconjugation, resonance.