The solvent effects on the formation of charge transfer complexes of imidazole with p-nitrobenzaldehyde (NBA) and 1, 3, 5-trinitrobenzene (TNB) have been studied by the spectrophotometric method. The molar ratio of imidazole to NBA and to TNB are found to be 1: 1 and 3: 1 in any solvent respectively. The equilibrium constants for the imidazole-NBA complex in acetonitrile, acetone, N, N-dimethylformamide and chloroform are 1.2, 1.4, 2.5 and 1.4 l/mol (25°C), respectively. The absorption spectrum of the imidazole-TNB system shows two absorption maxima at 420∼430 nm and 520∼530 nm. The former might be assigned to 7r-r transition in imidazole. The latter might be due to n-x transition in which the lone pair of nitrogen of imidazole takes part. It could be thought from these results that the hydrogen bonding of imidazole with each solvent might influence the formation of charge transfer complexes.
Amine-TNB-acetone systems form Meisenheimer type complexes. The values of logarithms of the rate constants of Meisenheimer type complex formation are proportional to pKb of amines. It is thought that the same process occurs in each amine-TNB-acetone system and imidazole behaves as a base catalyst as the other amines.