Spectroscopic studies of chemically liberated "free" -OH groups in aqueous N2H4, NH3, and CH3NH2 solutions

C. Austen Angell, Dana L. Fields

Research output: Contribution to journalArticle

3 Scopus citations

Abstract

As a contribution to understanding and identifying the nature of the disputed "broken" hydrogen bond in aqueous solutions we have sought to compare the spectroscopic character of "free" -OH groups produced by chemical means at constant temperature with that of the putative "free" -OH produced in pure water alcohols, etc. by temperature increases. "Free", or at least very weakly bonded, -OH groups have been produced quasi-stoichiometrically at room temperature by displacing bound -OH groups from OH⋯O bonds previously free with previously free -NH groups, the competitive status of which has been abruptly increased by protonation of the amine group. The sharp overtone bands of the unbonded -NH groups necessarily present in amine + H2O solutions (due to the excess of protons over lone pairs) disappear stoichiometrically on protonation using HClO4, and an equivalent number of weakly bonding -OH groups are produced. The spectroscopic signature of the chemically liberated -OH group is almost indistinguishable from that of the group liberated thermally, and a well-defined isosbestic point at 1442 nm (close to the approximate isosbestic point at 1440-1450 nm in the heated water spectra) implies that the same mechanism of "exciting across the centroid" (a (strong bond) ↔ (weak bond) exchange within a continuum model) is involved in each case.

Original languageEnglish (US)
Pages (from-to)4565-4569
Number of pages5
JournalJournal of physical chemistry
Volume89
Issue number21
StatePublished - Dec 1 1985
Externally publishedYes

ASJC Scopus subject areas

  • Engineering(all)
  • Physical and Theoretical Chemistry

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