Deuteron Quadrupole Coupling Constants of Hydrogen-Bonded Systems

A discussion of the electron distribution in the hydrogen‐bond system, O₁–D···O₂, in relation to the first‐order density matrix and the deuteron quadrupole coupling constant (DQCC), is presented. It is shown that the valence‐bond wavefunction of Coulson and Danielsson is only qualitatively useful. For the computation of the DQCC, a four‐electron, three‐basis orbital model appears to be inadequate. Theoretical values for DQCC which are somewhat comparable to experiment over a certain range of hydrogen‐bond length, O₁···O₂, is presented. These values are obtained with a 13‐electron molecular‐orbital model with ${\mathrm{sp}}^3$ hybrid orbitals. On the basis of the theoretical results the relation between the isotope effect and the DQCC is discussed. The empirical relationship between DQCC and the D···O₂ bond distance proposed by Soda and Chiba and the effect of hydrogen‐bond symmetry on DQCC are also examined.