Solvent-induced O-H vibration red-shifts of oxygen-acids in hydrogen-bonded O-H⋯base complexes

Sharon Keinan, Dina Pines, Philip M. Kiefer, James T. Hynes, Ehud Pines

Research output: Contribution to journalArticlepeer-review

11 Scopus citations

Abstract

Infrared spectroscopy has been used to characterize the solvent effect on the OH stretching vibrations νOH of phenol, 1-naphthol, 2-naphthol, 1-hydroxypyrene, and ethanol. We distinguish the dielectric (nonspecific) effect of the solvent on δνOH, the observed red-shifts in νOH, from the much larger red-shift caused by direct hydrogen (H)-bonding interactions with the solvents. To isolate the solvent dielectric constant ε effect on νOH, the OH oscillator was also studied when it is already H-bonded with an invariant oxygen base, dimethyl sulfoxide. We find that δνOH depends importantly on δPA, the difference between the proton affinities of the conjugate base of the proton donor and the proton acceptor. For a given H-bonded complex, νOH tends to vary inversely with ε, exhibiting different slopes for polar and nonpolar solvents, i.e., solvents comprising molecules with and without a permanent dipole moment, respectively. We use a two-state valence-bond-based theory to analyze our experimental data. This demonstrates that the OH oscillator acquires a more ionic-like character in the vibrational excited state, i.e., charge transfer; this results in a stronger H-bond in a more anharmonic potential for the OH vibration. The theory distinguishes between nonpolar and polar solvents and successfully accounts for the observed 1/ε and δPA variations.

Original languageEnglish
Pages (from-to)679-692
Number of pages14
JournalJournal of Physical Chemistry B
Volume119
Issue number3
DOIs
StatePublished - 22 Jan 2015

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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