INDOR study of 1H?1H inter-ring couplings in naphthalene derivatives

The ¹H n.m.r. spectra of two naphthalene derivatives have been completely analysed. The advantages of the INDOR technique have been illustrated in the determination, magnitudes and signs, of small couplings in complex spin systems. A splitting of 0.07 Hz has been resolved in the 100 MHz spectrum of 1,2-dichloro-3 nitronaphthalene. The signs of the inter-ring coupling constants alternate with the number of intervening bonds.