An extension of Mulliken's charge‐transfer theory leads to a relation between the enthalpy of formation and the enhancement of the dipole moment for hydrogen‐bonded complexes. Extensive experimental data are in accord with this theoretical prediction. It is shown conclusively that the proton transfer effect is not responsible for the enhancement of the dipole moment in these systems.

Charge‐transfer properties of hydrogen bonds. III. Charge‐transfer theory and the relation between the energy and the enhancement of dipole moment of hydrogen‐bonded complexes

The dependence of the deuteron quadrupole coupling constant (DQCC) on the nature of hybridization of carbon in deuterocarbons is examined in detail. A simple molecular orbital description of the C–D fragment, with various effective nuclear charges on carbon, is used. The calculated values are shown to be comparable to experimental results and other theoretical models which treat the entire molecules rather than simply the C–D fragment. It is shown that DQCC(sp) > DQCC(sp2) > DQCC(sp3) which may be attributed to the fact that the nuclear contribution to the electric field gradient decreases faster than the electronic part in the series sp, sp2, sp3. A collection of experimental data, establishing the same trend obtained theoretically, is presented including new deuterium NMR results on phenylacetylene‐d and ferrocene‐d10.

Deuteron Quadrupole Coupling Constants in Deuterocarbons

The temperature dependence of the quadrupole splitting of the deuteron magnetic resonance spectra of KD2AsO4 and CsD2AsO4 has been studied and the electric field gradient tensors at the deuteron sites were determined. The results show that the deuterons are—similar to those in KD2PO4—moving between the two off‐center positions in the O–D···O bonds above Tc and are effectively frozen in at one of the two possible sites below Tc. The dynamics of this process was investigated by deuteron spin–lattice relaxation studies. The results show the existence of a “soft” deuteron mode which condenses at Tc, but cannot distinguish between a pure relaxational and an overdamped resonant mode.

Deuteron Magnetic Resonance and Relaxation in Ferroelectric KD2PO4, KD2AsO4, and CsD2AsO4

For pt.I see ibid., vol.16, p.6129 (1983). Proton second moment, T1H.T1 rho H and T111B measurements over the temperature range 330K>T>46K are reported. At low temperatures tunnelling of the protons of the NH3 group influences the second moment and T1 rho H results seriously. An analysis of the results has yielded a tunnelling frequency ft=1.4 MHz at 85K. In the low-temperature orthorhombic phase (T 225K) the BH3 groups and possibly the NH3 groups rotate freely. The activation energy associated with the BH3 motion is 1.4+or-0.1 kcal mol-1. The high degree of plasticity of the crystals in this phase is attributed to the increased disorder. Strong evidence for piezoelectricity has been found in the tetragonal phase. The orientation of the B-N bonds is the same in both phases and, except for a very slow motion that starts at about 300K, no evidence has been found for a reorientation of the entire H3N.BH3 unit. The temperature dependence of the unit-cell dimensions is discussed in terms of the reorientational rates of BH3 and NH3 groups.

http://iopscience.iop.org/article/10.1088/0022-3719/16/32/008/pdf

R. Blinc

Papers

Magnetic Resonance in Hydrogen-Bonded Ferroelectrics