Nuclear quadrupolar couplings are sensitive probes of hydrogen bonding. Experimental quadrupolar coupling constants of a deuterons (D-alpha QCC) are reported for the residues of human ubiquitin that do not experience large-amplitude internal dynamics on the pico- to nanosecond time scale. Two different methods for D-alpha QCC estimation are employed: (i) direct estimation of D-alpha QCC values from R-1 and R-2 H-2 D-alpha rates using the dynamics parameters (S-C alpha-H alpha(2)) derived from 1 mu s molecular dynamics simulations as well as from C-13(alpha) relaxation measurements and (ii) indirect measurements via scalar relaxation of the second kind that affects C-13(alpha) relaxation rates in C-13(alpha)-D-alpha spin systems. A relatively large variability of Da QCC values is produced by both methods. The average value of 170.6 +/- 3 kHz is derived from the combined data set, with Da QCC values ranging from 159.2 to 177.2 kHz. The set of lowest quadrupolar couplings in all data sets corresponds to the residues that are likely to form weak C-alpha-H-alpha center dot center dot center dot O=C hydrogen bonds as predicted from the analysis of short H-alpha center dot center dot center dot O distances in three-dimensional structures of ubiquitin. These D alpha nuclei show up to 10 kHz reduction in their QCC values, which is in agreement with earlier solid-state NMR measurements in alpha deuterons of glycine. A statistically significant correlation is observed between the QCC values of alpha-deuterons and the inverse cube of C-alpha-H-alpha center dot center dot center dot O=C distances in ubiquitin.