Linear free energy relationships in the thiophen series. Part I. Leaving group effect in piperidino-substitution in methanol of some 2-L-3-nitro-5-X-thiophens

Abstract

The reaction rates at various temperatures for piperidino-substitution of some 2-L-3-nitro-5-X-thiophens (L = Cl, Br, I, OC₆H₄NO₂-p, or SO₂Ph; X = H, Br, CONH₂, CO₂Me, SO₂Me, Ac, CN, or NO₂) have been measured in methanol to give information on the influence of the leaving group and the substituent at C-5 on the position of the rate-determining transition state (r.d.t.s.) on the reaction co-ordinate. Taking into account the effects (electronic and steric) of the leaving group, the data obtained have been explained by a modified interpretation of the ρ values obtained. The ρ values give a measure of the sensitivity of the reaction to the changes in the position of the r.d.t.s. on the reaction coordinate as a function of the substituent at C-5. Dependence on the type of t.s. (early or late) is also shown.