Prediction of tautomeric equilibria for N,N′,N″-trisubstituted, N,N′-disubstituted and N-monosubstituted guanidines

Abstract

The methods, based on Brønsted acid–base equilibria, for prediction of the tautomeric equilibria constants (as pK_T) and of the pK_a values of individual tautomers are proposed, and applied to N,N′,N″-triaryl-, N,N′-diaryl-, and N-aryl-guanidines. The tautomeric equilibria constants obey a linear relation with σ° constants: pK_T=–ρ_TΔσ°.