Grant-Cheney approach

The upfield shift of signals of carbon atoms in 7-position to a newly introduced substituent was recognized very early. Grant and Paul (169) found a 7-parameter of —2.5 in linear and branched alkanes. Later this group studied various other classes of hydrocarbons (33,88,100,101,170-172) and developed an interpretation of the 7-effects in terms of a polarization of the bond between the carbon concerned and an adjacent, sterically perturbed hydrogen atom (33,88) that has come to be called the Grant-Cheney approach. ... 

Schneider and co-workers (159) attempted to rescue the Grant-Cheney approach, at least for methyl substituents. They refined it by using a modified potential for the repulsive force (186) along with fully relaxed molecular structures as determined by force-field calculations. This indeed led to a satisfactory correlation of yg-SCS(CH3) with repulsive interactions in methylcyclohexane and some methylbicyclo[2.2.1]heptanes (159). Schneider s treatment, however, implies that a signal shift originates not only from steric H-H repulsion but includes effects from secondary carbon-framework distortions (85,159). 

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