Dissociation constants of thiophencarboxylic acids: calculation of ? constants for the thiophen ring

Abstract
Dissociation constants for a number of substituted thiophen-5-carboxylic acids have been determined and used to evaluate σ constants for the thiophen molecule. The values obtained are in excellent agreement with those calculated by the method of Dewar and Grisdale and indicate that the sulphur atom has very little effect upon the transmission of substituent effects across the ring.