Use of the Hammett equation in substituted thiophenes

The application of multivariate statistics to linear free-energy relationships in the thiophene series increases the understanding of the Hammett equation. Principal components analysis shows that α-substituted thiophenes require the σ constants used for pars-substituted benzene derivatives, owing to a strict proportionality of the substituent effects in the heterocyclic and homocyclic systems. Partial least-squares analysis indicates that two independent effects are linearly transferred from benzenes to thiophenes.