INFRARED-SPECTRA AND MOLECULAR-ORBITAL STUDIES OF HYDROGEN-BONDED COMPLEXES OF 2-CHLORO-4-NITROBENZOIC ACID

Infrared spectra from complexes of 2-chloro-4-nitrobenzoic acid and so me amines with proton affinities (PA) ranging from 205.9 to 229.4 kcal mol(-1) are studied. A characteristic relationship between the center of gravity of the infrared protonic vibrational band and proton affin ity is obtained. A theoretical study using the atom superposition and electron delocalization molecular orbital method (ASED-MO) is performe d. A good correlation between the theoretical and experimental results is found, both theoretical and experimental results showing that the 3,5-dimethylpyridine complex represents the critical point at which 50 % proton transfer is obtained.