The syntheses and multinuclear NMR spectroscopic data for a series of Mo(CO)5(PPh2XR) (X = O, NH; R = 1-4 carbon alkyls) complexes is presented. The steric effect of substitution at the α carbon of the R groups is shown to have an effect on the chemical shifts of the aromatic C(l) 13C, 31P, and 95Mo resonances but not upon the chemical shifts of the carbonyl 13C and 17O resonances. In addition, the good correlation observed between the chemical shifts of the 95Mo and aromatic C(l) 13C resonances indicates that in the Mo(CO)5(PPh2XR) complexes, the 95Mo and aromatic C(l) 13C resonances are similarly affected by changes in the R group. © 1983, American Chemical Society. All rights reserved.