Azide ion as a nucleophile

It is convenient to commence a discussion of the reactivity of azide ion in protic solvents vith reference to aromatic Sn reactions since these have been investigated in greater depth than aliphatic 

It is instructive to compare the nucleophilic strength of azide ion with that of amide and substituted amide ions. The significant difference is the low electron affinity of the amino group amide ions are therefore much stronger nucleophiles than azide iou. They are also very strong bases with reactivity such that they cannot be used in protic solvents which are stronger acids than the conjugate acids of amide ions, viz. amines. 

Although the rates of azide exchange reactions have not been studied, it may be predicted that the enhancement of reactivity due to the electronegativity factor would be largely counteracted by the relatively greater stability of initial states in their reactions with azide 

In 5 nI reactions of aliphatic substrates it is important to note that the electrophile is a carbonium ion and this is much less discriminating towards nucleophiles than are less reactive electrophilic species. In such reactions the nucleophilic strength of azide ion has no direct effect on rates, but is involved in determining product ratios in competitive reactions with other nucleophiles, including the solvent. Concentration factors are therefore important and salt effects of dissolved azides may also be significant -. 

5n2 processes, although the ratios are a little larger than those typical with oxygen nucleophiles. 

---