ELECTRON COUPLING OF NUCLEAR SPINS. V. VIBRATIONAL EFFECTS IN CHX GROUPS
ILLINOIS UNIV URBANA NOYES CHEMICAL LAB
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A study was made to determine whether vibrational and isotopic effects are of any consequence in the H-H, H-D, H-F, and D-F coupling constants for CH2, CHD, CHF, and CDF groups. The angular dependence of the proton-proton coupling constant in CH2 groups between bond angles of 100 and 130 degrees was calculated at 5 degree intervals. The predicted values are larger than those previously observed at small H-C-H angles as well as at large angles. Graphical interpretation indicated that the variation of the coupling constant with bond angle is somewhat non-linear, i.e., the coupling changes more rapidly at smaller bond angles. Vibrational averaging is shown to be independent of temperature for CH2 and CHD groups. In the study of the angular dependence of H-F coupling in CHF groups an effort was made to detect a difference between samples of C3F7H and C3F7D. Observations of the F-9 spectra of the 2 compounds at 40 mc revealed no difference.