G2(MP2) Characterization of Conformational Preferences in 2-Substituted Ethanols (XCH₂CH₂OH) and Related Systems

The preferred conformation of species of the general form XCH 2 −CH 2 Y can be gauche (X = Y = F or X = F, Y = Me) or trans (X = F, Y = Cl or Br, and [X, Y] = [Cl, Br]). If either or both of X or Y = OH, then new degrees of freedom open, and the possibility of H ···X interaction complicates the picture. We present G2MP2 calculations on the series, which represent the preferences faithfully. NBO analyses of DFT densities help us to understand the patterns of conformational preferences. We address the question of whether hydrogen bonding as generally understood plays a central role in establishing preferences in the alcohols and diols. A consistent account of conformational preferences can be founded on simple notions of electrostatic attraction.