Tautomerism, Hammett sigma, and QSAR.

A consideration of equilibrium model-based equations suggests that tautomeric equilibria do not markedly affect observed potency if the tautomer bound represents at least 50% of the compound in solution. Tautomeric equilibria can enhance or attenuate the correlation of potency with Hammett sigma. Additionally, tautomeric equilibria can lead to a correlation of potency with sigma even in the absence of a correlation of binding with sigma.