Charge-transfer complexes between iodine and styrylpyridines. Part 2.—Substituent effect

Abstract

The effect of substituents on the charge-transfer equilibria between iodine and isomeric styrylpyridines has been studied spectrophotometrically in n-hexane or dichloromethane solutions. The effect of methyl-substitution in the pyridine ring and of different para-substituents in the benzene ring has been investigated for cis- and trans-2-styrylpyridines and for trans-3- and 4-styrylpyridines, respectively. The results are discussed in terms of steric and electronic factors. The relation between the charge-transfer stability constants and the acidity constants has been examined. The results are also reported for some experiments performed with the aim to demonstrate a partial interaction of iodine with the π system.