INFRARED STUDY OF THE HYDROGEN-BONDING ABILITY OF 3-AMINOQUINOLINE AND 8-AMINOQUINOLINE

The geometry and the complexing ability of 3-aminoquinoline (3-AQ) and 8-aminoquinoline (8-AQ) are investigated by infrared spectrometry in carbon tetrachloride solution. The study of the NH(D) stretching vibrations in partially N-deuterated 8-AQ suggests that the two NH(D) bonds are not equivalent and this is accounted for by the presence of a weak intramolecular NH ... N hydrogen bond. The complexes between 3-AQ and 8-AQ and phenols are studied. The thermodynamic data (K,-Delta H, Delta S-o) and the frequency shifts of the v(OH) stretching vibration are much higher for the 3-AQ than for the 8-AQ complexes. This is accounted for by the peri-interaction in 8-AQ. Complex formation with phenols brings about an increase in the frequencies of the NH2 stretching vibrations. The observed differences between the two systems suggest that in the 8-AQ-phenol complexes a secondary NH ... O interaction may exist. The complexes between 3-AQ or 8-AQ and strong proton accepters (pyridine, triethylamine) are also studied. The perturbations of the NH2 stretching vibrations suggest that in the 8-AQ complexes the intramolecular NH ... N hydrogen bond is weakened, in agreement with the cooperativity theory.