Further consideration of the gas–liquid chromatographic method for determining the intramolecular hydrogen bond energies with the example of 2-substituted phenols

The GLC method for determining the intramolecular hydrogen bond (intra-HB) energy as the difference between the heats of dissolution of two isomers, one of which forms an intra-HB and the other has no such bond for steric reasons, in a polar stationary liquid phase was further considered by taking account of a correction for the difference between the energies of nonspecific interactions of the isomers with a polar phase. With 4- and 2-substituted phenols as an example, the differences between their heats of dissolution in polyethylene glycol and in poly-1,4-butanediol succinate were measured. As a first approximation, corrections for the contribution of the energy of nonspecific interactions with a liquid phase to the total magnitude of the difference between the heats of isomer dissolution were found. These corrections were determined as the difference between the heats of dissolution for 1,4- and 1,2-disubstituted benzene derivatives—analogs of the compounds under study that either do not have hydroxyl groups altogether or, in the case of 1,2-isomers with a hydroxyl group, cannot form an intra-HB. On the basis of the obtained results, the average intra-HB energies of 2-fluoro- (1), 2-chloro- (2), 2-bromo- (3), 2-iodo- (4), 2-methoxyphenol (5), salicylaldehyde (6), methyl ether of salicylic acid (7) and 2-nitrophenol (8) were estimated to be 7.4 ± 0.3, 13.3 ± 0.8, 14.4 ± 0.4, 12.8 ± 0.3, 17.6 ± 0.1, 24.6 ± 1.2, 29.8 ± 0.3 and 32.5 ± 4.7 kJ/mol, respectively. The values were compared with those found in the literature.