Addition of cyanide ion to nicotinamide cations in acetonitrile. Formation of non-productive charge-transfer complexes

The mixing of equal volumes of 0.2 mmol dm–3 1 -benzylnicotinamide ion and 2 mmol dm–3 cyanide ion results in the immediate formation of a transient absorption band at 375 nm which can be ascribed to a charge–transfer complex. This complex disappears within ca. 0.2 s with the formation of the 1,6-addition product which, in turn, is rapidly converted into the thermodynamically more stable 1,4-adduct. Methyl substitution at the 6-position of the nicotinamide ring inhibits the formation of the 1,6-adduct, resulting in an increase in the lifetime of the charge–transfer complex. Subsequently a mixture of the 1,4-cyanide adduct and, most likely, the 1,2-adduct is formed. Rate effects with variation of substituents in the 1-benzyl group reveal that charge-transfer complex formation is counter-productive to the formation of addition products.