13C, 13C coupling constants in anthracene, 9,10‐dihydroanthracene and phthalic acid derivatives. Determination of signs by the symmetrical double labelling (SDL) method V

Carbon‐13, carbon‐13 one‐bound and long‐range coupling constants are determined for anthracene and 9,10‐dihydroanthracene labelled in the 9,10‐positions, and for thiophthalic anhydride and phthalimide, labelled in both carbonyl groups. Relative signs are determined by the SDL method. Signs in naphthalene, anthracene and pyrene derivatives are discussed. The general trends observed in many aromatic compounds, 3J|>|2J|>|4J| and 2J positive, 3J positive, 4J negative are mostly confirmed. However, evidence suggests that two‐bond couplings between carbon atoms in the same ring in aromatic hydrocarbons are negative.