Heteroaromatic rings as substituents. Part IV. The ‘non-constancy’ of the σp+ constants of the 2-thienyl and 2-furyl groups

Abstract

The σ_m⁺ and σ_p⁺ constants for the 2-thienyl group have been calculated from the rates of solvolysis of 1-(2-thienylphenyl)ethyl acetates in aqueous 30% ethanol. A comparison with the values previously determined from similar reactions shows that, whereas the σ_m⁺ value is constant, the σ_p⁺ value varies within wide limits. The σ⁺ constants for the 2-thienyl and 2-furyl groups have also been calculated from the carbonyl stretching frequencies of thienyl- and furyl-substituted acetophenones by applying the Traylor and Ware correlation. The possible reasons for such ‘non-constancy’ of the σ_p⁺ values for these ‘aromatic’ substituents are discussed.