Temperature dependence of the deuterium quadrupole coupling constants and the correlation times for neat formamide

High-level ab initio calculations yield a linear relationship between the p roton chemical shift, delta(H), and the deuterium quadrupole coupling const ant, chi(D), for the amide protons in neat, liquid formamide. An experiment al measurement of delta(H) in combination with the linear relationships pro vides an accurate value for chi(D) in the hydrogen-bonded liquid; subsequen t measurements of the deuterium relaxation rate provide a means to obtain e ffective rotational correlation times in the neat liquid. Temperature-depen dent proton chemical shifts and relaxation rates for the three nuclei in fo rmamide are presented. The chemical shift data and the ab initio calculatio ns indicate that both amide protons hydrogen bond, whereas the C-H proton d oes not participate in hydrogen bonding in the neat liquid. The effective c orrelation times at room temperature were found to be 9.2 ps for the trans N-D vector, 6.3 ps for the cis N-D vector, and 5.2 ps for the C-D vector. T his indicates that in the neat liquid formamide rotates anisotropically.