J. Derkosch, W. Mikenda, E. Steinwender
1987
Citations
0
Influential Citations
7
Citations
Journal
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy
Abstract
Abstract I.r.-, NMR- and u.v.-data of 2-hydroxy-(dithio)benzoic acid and N,N-disubstituted 2-hydroxy-(thio)benzamides are presented, which provide a direct comparison between analogous OH … O and OH … S type hydrogen bonds. In dilute CCl4 solution the OH groups of the (thio)amides are intramolecularly associated, with the OH stretching frequencies being slightly smaller and the proton shifts being larger for OH … O ( ν liq = 3200–3250 cm−1, δ = 9.95-8.95 ppm) than for OH … S ( ν liq = 3245–3330 cm−1, δ = 8.09-7.06 ppm) bonds. As a result of increasing steric hindrance the hydrogen bond strengths slightly decrease within the series dimethylamide > piperidide $ morpholide > dimethylpiperidide for both, oxo- and thio-compounds. In the crystalline state the OH groups of the (thio)amides are intermolecularly associated, with the OH stretching frequencies again being smaller for OH … O ( ν sol = 3075–3140 cm−1) than for OH … S ( ν sol = 3130–3315 cm−1) bonds, however the correspondence is less systematic and the differences are somewhat more pronounced than is the case for the solutions. Contrary to the (thio)amides the hydrogen bond of the phenolic OH group of salicylic acid, which is an intramolecular one in dilute solution, as well as in the crystalline state, is much more weak ( ν liq = 3210 cm−1, δ = 10.21 ppm; ν sol = 3230 cm−1) than the OH … S bond in dithiosalicylic acid ( ν liq = 2950 cm−1, δ = 12.20 ppm; ν sol = 2750 cm−1). The results are discussed with respect to systematic differences between analogous OH … O and OH … S hydrogen bonds.