A theoretical investigation of steric effects on 1H chemical shifts of camphor and norcamphor derivatives

Camphor and norcamphor derivatives provide convenient models for testing and evaluating some of the results of our work on substituted adamantanes and for checking their applicability to other systems. Our results show that the reduction in C-H bond lengths associated with steric interactions are not as pronounced in systems that are less rigid. Deshielding of 1H chemical shifts on introduction of the substituent in exo and endo positions can also be traced to angular distortions which are stronger in norcamphor, bornane and camphor than in norbornane due to additional steric interactions with a carbonyl group, with methyl groups, or with both. 1H chemical shifts are sensitive probes for steric effects, reflecting differences in bond lengths, bond angles and dihedral angles in a systematic way. Given the proper models for comparison purposes they can be used to evaluate the size of a certain group and locate its interactions with the rest of the molecular framework.