Synergistic Spectroscopic and Computational Characterization Evidencing the Preservation or Flipping of the Hydroxyl Group of 2-Phenylethyl Alcohol upon Single and Double Hydration.

Abstract

Even apparently simple, obtaining and analyzing observations on molecules and clusters and unambiguously assigning their structures is challenging. We report here the first ionization-loss Raman spectra compared to quantum chemical predictions for establishing the structural preferences of hydrates of the neurotransmitters hydroxy analogue, 2-phenylethyl alcohol (PEAL). The spectra encode two monohydrates and two previously unnoticed dihydrates, consequences of water insertion and sidewise attachment to the O-H group of gauche PEALs, in PEAL-H2O and PEAL-(H2O)2, or the higher-energy gauche-trans PEAL in the latter. The electronic structures retain the stable PEAL or flip its O-H to convert the gauche-trans PEAL conformer to the global minimum-energy dihydrate. We disclose conventional and bifurcated hydrogen bonds and electron steric repulsions by noncovalent interaction analysis and correlations between the experimental O-H stretching vibrational frequencies and the O-H and H···X bond lengths and electron densities, pointing to implications on hydrate forms and our approach virtue.