Spectroscopic studies of chemically liberated "free" hydroxyl groups in aqueous hydrazine, ammonia, and methylamine solutions

Abstract

The spectroscopic character of free -OH groups produced by chemical means at constant temperature is compared 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 + H/sub 2/O solutions (due to the excess of protons over lone pairs) disappear stoichiometrically on protonation using HClO/sub 4/, 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) in equilibrium (weak bond) exchange within a continuum model) is involved in each case. 13 references, 7 figures.