Title

Study of hydrogen bonds of hypophosphorous acid by <sup>1</sup>H, <sup>2</sup>H, <sup>31</sup>P, and <sup>15</sup>N NMR spectroscopy under slow exchange conditions.

Authors

Golubev, N. S.; Asfin, R. E.; Smirnov, S. N.; Tolstoi, P. M.

Abstract

The NMR spectra of solutions containing partially deuterated anhydrous hypophosphorous acid (H2POOH) and its complexes with organic bases as proton acceptors were obtained in CD2Cl2 in the temperature range 183–253 K. Under these conditions, the state of slow exchange is achieved, as evidenced by the fine spin-spin and isotope (H/D) structure of the NMR signals. The formation and strengthening of the hydrogen bond by the OH group result in strong shielding of the 31P nucleus and decrease the spin-spin coupling constants of nuclei in the PH2 group. Saturation of these effects occurs in going from proton to base. Direct and long-range effects of H/D substitution in the OH and PH groups on the H, 31P, and 15N chemical shifts in complexes were measured. The signs of these effects were explained in terms of a simplified model of dynamic interaction of covalent and hydrogen bonds. The kinetics of the interconversion of a cyclic H2POOH dimer and a zwitterionic complex with pyridine were studied by dynamic 1H NMR, and thermodynamic and kinetic parameters of the process were measured. A hypothetical mechanism of the reaction with the transition state close to an open-chain dimer with one hydrogen bond was proposed.

Subjects

HYDROGEN bonding; MOLECULAR association; NUCLEAR magnetic resonance spectroscopy; ORGANIC bases; BASES (Chemistry); ORGANIC chemistry

Publication

Russian Journal of General Chemistry, 2006, Vol 76, Issue 6, p915

ISSN

1070-3632

Publication type

Academic Journal

DOI

10.1134/S1070363206060119