NMR—the chemical shift—IV (original) (raw)

Abdmet-Tk caIcuIation of chemical shift values by the metbod used in Part I has been extended to a derivation of the shielding et&t of the ketonic CO group. Tbe calculations include consideration of both the magnetic anisotropy screening and tbe electric Fold scwning effect in this substituent. Using the complete series of mowketoandtostanes, tbe values of tbe anisotropies of tbe C==O doubk bond and of K, a parameter descriptive of tbe electric screening effect, have been derived for various, coincidental locations of the magnetic and electric dipoles along tbe >c-O bond. As with tbe C=C double bond, our results necessitate a substantial modification of the conventional pictute of the shielding 'cone' around the CO group.