CONFORMATIONAL EQUILIBRIA IN 2-AMINO-1,2-DIPHENYLETHANOL SYSTEM .2. INFRARED STUDIES

Conformational preferences in a series of 2-(N,N-dialkylamino)-1,2-diphenylethanols (1a-d) have been examined by means of high-dilution infrared spectroscopy. With a single exception (1c) the dl-threo amino alcohols reveal a single, intense absorption band in the 3-µ region, assigned to an intramolecular OH⃛N bond. In contrast, three absorption bands appear in the spectra of the dlrerythro amino alcohols, attributable, in order of decreasing frequency, to the presence of unassociated OH, intramolecular OH ⃛π bonding and intramolecular OH⃛N bonding. These data are entirely consistent with the assignment of conformational preferences based on nmr, i.e., the conformation of the dl-threo amino alcohols (1c excepted) may be adequately represented by a single rotamer, tA, and that of the dl-erythro amino alcohols by an equilibrium mixture of rotamers, eA and eB. © 1969, American Chemical Society. All rights reserved.