Competing intramolecular vs. intermolecular hydrogen bonding in phosphoryl-containing secondary alkanols: A structural, spectroscopic and DFT study

Abstract

Intramolecular hydrogen bonding competes with intermolecular hydrogen bonding in alkanols containing Ph2P(O) group. A character of H-bonding in secondary alkanols Ph2P(O) (CR2)nCH2CH(OH)Me, where n = 0 (1), n = 1, R = H (2), and n = 1, R = Me (3) in crystal state and solutions has been studied by X-ray diffraction, FTIR, and diffusion ordered NMR spectroscopy (DOSY). Quantum chemical calculations and QTAIM analysis of isolated alkanol molecules and their dimers have been performed. In spite of slight difference in the structure of linker between P(O) and OH groups, the studied alcohols in crystal exhibit three types of H-bonds: dimer with intermolecular H-bond, polymeric chains with intermolecular H-bond, and monomer with intramolecular H-bond. Experimental data agree well with structural data of quantum chemical calculations at the M06-2x/6-311G (d,p) level of theory. Energy values (thermodynamic parameters) of DFT-optimized structures for gauche and anti isomers and dimers have been calculated. According to FTIR data in solutions (0.1–0.0001 M), alcohol 1 is the most associated, association of alcohol 2 is much less expressed, while alcohol 3 remains as H-bound monomer. Particle size assessed by DOSY relative to Ph3CH does not change on dilution for alcohols 2 and 3 but varies for alcohol 1.