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

Evenapparently simple, obtaining and analyzing observations onmolecules and clusters and unambiguously assigning their structuresis challenging. We report here the first ionization-loss Raman spectracompared to quantum chemical predictions for establishing the structuralpreferences of hydrates of the neurotransmitters hydroxy analogue,2-phenylethyl alcohol (PEAL). The spectra encode two monohydratesand two previously unnoticed dihydrates, consequences of water insertionand 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 stablePEAL or flip its O-H to convert the gauche-trans PEAL conformer to the global minimum-energydihydrate. We disclose conventional and bifurcated hydrogen bondsand electron steric repulsions by noncovalent interaction analysisand correlations between the experimental O-H stretching vibrationalfrequencies and the O-H and H & BULL;& BULL;& BULL;X bond lengthsand electron densities, pointing to implications on hydrate formsand our approach virtue.

Automated summary

In this study, we used ionization-loss Raman spectroscopy in combination with quantum chemical predictions to determine the structural preferences of hydrates of the neurotransmitter analogue 2-phenylethyl alcohol (PEAL). Our findings revealed two monohydrates and two previously unnoticed dihydrates, which resulted from water insertion and sidewise attachment to the O-H group of gauche PEALs. The electronic structures either retained the stable PEAL conformer or flipped its O-H group to convert it to the global minimum-energy dihydrate conformer.