Principal component analysis of the 13C NMR shifts of norbornyl derivatives

Principal component analysis was applied to the 13C NMR chemical shifts of the seven carbon atoms of the norbornyl framework for 75 molecules. Two two‐dimensional principal component projections are shown to be sufficient to distinguish the main electronic and steric substituent effects contributing to these shifts. These effects allow a comparison of the (three‐, four‐ and five‐membered) ring and non‐ring substituents and their influence on the shifts of carbon atoms of the norbornyl framework. Four classes of molecules, each with characteristic chemical behaviour, are identified. Exo‐endo class discrimination and exo‐endo patterns of isomer pairs are emphasized, especially with regard to cyclic substituents on norbornyl systems.