Substituent chemical shifts in NMR. 3—Carbonitrile SCS in rigid molecules†

The complete analysis of the 1H NMR spectra of 2-norbornene carbonitrile (exo and endo), 2-norborname carbonitrile and (exo and endo)1-adamantane carbonitrile is reported, using high-field NMR and COSY and proton-carbon correlation experiments to assign the spectra, these data, together with a previous analysis of 1-octadeuteriocyclohexane carbonitrile, when combined with data for the parent hydrocarbons provide an extensive data set of substituent chemical shift (SCS) values Cor carbonitriles in molecules of accurately known geometry. The change in geometry on the introduction of a CN group was investigated using ab initio and MNDO methods, and found to be negligible for the carbon framework but significant around the C–N bond for the endo derivatives. A noteworthy feature is that the shielding of the 3x and 3n protons in the norbornane carbonitriles cannot be explained by the magnetic anisotropy of the CN bond.