A view of thermodynamics of hydration emerging from continuum studies.

Frequencies and intensities are calculated by ab initio methods for all vibrational modes of the 1:1 H3X–HF and 1:2 H3X–HF–HF complexes (X=N,P). The HF stretching frequencies are subject to red shifts, roughly proportional to the strength of the H bond, and to manyfold increases in intensity. Although the intramolecular frequency shifts within the proton acceptors are relatively modest, the intensities of the NH3 stretches are magnified by several orders of magnitude as a result of H bonding (in contrast to PH3 which exhibits little sensitivity in this regard). The frequencies and intensities corresponding to bending of the H3X–HF H‐bond rise with increasing H‐bond strength while the properties of the other intermolecular modes appear somewhat anomalous at first sight. The intensity patterns are analyzed by means of atomic polar tensors which reveal that intensification of the proton donor stretch is chiefly due to increasing charge flux associated with H‐bond formation. The different behavior of the N–H ...

/pdf/vibrational-frequencies-and-intensities-of-h-bonded-systems-19dlah3fmz.pdf

Vibrational frequencies and intensities of H‐bonded systems. 1:1 and 1:2 complexes of NH3 and PH3 with HF

Intermolecular interactions and tautomerism of nucleic acid bases and their analogues

The structures, association energies, and vibrational frequencies and IR intensities of the dimers of water and nitrous oxide were examined using the SCF method with MINI-1 and 4-31G basis sets. The small shifts in the frequencies and the changes in intensity upon dimerization N2O·H2O → (N2O)2 suggests weak interactions in these complexes. The thermodynamic characteristics of the dimerization processes and the breaking of the hydrogen bond in the water dimer by nitrous oxide are presented. The equilibrium constant for the latter process is very low which means that nitrous oxide is a weak anaesthetic.

M. M. Szczesniak

Papers

Search for simplified procedure for the evaluation of the Gibbs free energy of hydrogen-bond formation