In this report we initiate analysis of imidazole rings bound to metals using one-bond H-1-C-13 couplings. Shift trends in the metal binding of N-donor heterocyclic ligands have been difficult to interpret since signals of close-in nuclei, particularly the carbon in the CN2 grouping of imidazole rings, often have erratic or small shift changes. We exploit the well-studied trans influence of a series of unidentate axial R and X ligands in cobaloxime complexes (LCo(DH)(2)(R or X)) since shifts of carbons remote from Co have interpretable trends that correlate with Co-N bond lengths. We compare information obtained from (1)J(CH) values for two series, one with L = a small ligand, N-methylimidazole (N-MeImd), and one with L = a large ligand, 1,5,6-trimethylbenzimidazole (Me(3)Bzm). For comparison to our spectroscopic measurements, we have determined X-ray crystal structures for N-MeImdCo(DH)2(R or X) (where DH = monoanion of dimethylglyoxime, R or X = CH2CH3 (1), CH3 (2), CH2CN (3), and Cl (4)) doubling the number of structures reported for cobaloximes containing N-MeImd. The observation of the B-type orientation of the planar N-MeImd axial ligand in structures I and 2 almost certainly results from the small size of N-MeImd. This B-orientation is rare for cobaloximes, which normally have an axial ligand in the A-orientation. The t scores obtained from the principal component analysis of cobaloxime data [Randaccio, L.; Geremia, S.; Zangrando, E.; Ebert, C. Inorg. Chern. 1994, 33, 4641] were applied for the first time in the analysis of intraligand coupling constants. The use of these parameters allowed us to identify steric effects on the C-13 shifts and (1)J(CH) values for the bulky, lopsided Me(3)Bzm axial ligand in the Me(3)BzmCo(DH)(R or X) series; similar steric effects on spectra were not observed for N-MeImdCo(DH)(R or X). The intraligand (1)J(CH) values for the close-in N2CH carbon of Me(3)Bzm and N-MeImd were found to reflect the ligand-to-metal binding even better than the more commonly used C-13 shifts Of carbons remote from the metal. Thus, the use of (1)J(CH) values holds considerable promise in metallobiochemistry.