Carbon
-carbon coupling constants of 1-phenylazo-2-naphthol and 2-phenylazo-1-naphthol have been measured with the SEMINA-1 pulse sequence. The carbon-carbon couplings provide an unambiguous assignment of the uC spectra. The magnitudes of the carbon-carbon coupling constants are discussed in relation to the tautomeric nature of the compound. Substituent effects on couplings are also considered. KEY WORDS 13C NMR, Carbon-carbon coupling constants Phenylazonaphthols ' NNMR spectro~copy.'-~ The C chemical shifts of the phenyl ring carbons are easily assigned, and are useful in the quantitative determination of the azo and hydrazo content.' However, the assignment of the ring carbons of the naphthalene moiety is difficult owing to the lack of exact reference data and the lability of the equilibrium, and several conflicting assignments of the 13C spectrum e ~i s t . ' , ~, ~. This paper presents carbon-carbon coupling constants measured with the new SEMINA-1 pulse sequence.' This sequence performs spectral editing of the INADEQUATE' experiment, dividing the spectra into two categories according to the number of & 2" y Q , / 2'