Carbon-13 nuclear magnetic resonance examination of benzonorbornene derivatives. Assignment of site of aromatic ring substitution in benzonorbornen-2-ones

13C nuclear magnetic resonance spectra were collected for a series of 5‐ and 6‐monoaromatic ring‐substituted benzonorbornadienes and 5‐, 6‐, 7‐, and 8‐monosubstituted benzonorbornen‐2‐ones. 13C chemical shifts values were found to be useful in the differentiation of the four monosubstituted aromatic ring isomers of benzonorbornen‐2‐one (1). We found that the 13C NMR spectrum of a substituted benzonorbornen‐2‐one (A) could be predicted with good accuracy (R2 for each aromatic carbon ≥ 0.925) from a knowledge of the 13C NMR spectrum of 1 and the appropriately substituted benzene. The substituents studied were NO2, NH2, I, CF3, CN, OCH3, and H. Correlation analysis showed that the carbonyl in A was effectively insulated from the ring π‐system.