$^{13}C$ NMR spectra of 1,3-dipyridyl- and pyridylphenylthioureas. Chemical shift assignments and conformational implications

The $^{13C}$ NMR spectra of a series of 1,3-dipyridyl- and pyridylphenylthioureas have been obtained. Complete analyses of the experimental spectra have provided the chemical shifts and coupling constants. The spectra of dipyridylthioureas over a temperature range showed important changes which could be attributed to an intramolecular conversion between the two equivalent E,Z and Z,E conformations. The coalescence temperature of the $^{13}C$ signals leads to a \Delta G* of \sim 58.0 kJ $mol^{-1}$ for the dynamic process involved. The results show that pyridylphenyl thioureas exist in a single conformation at ambient temperature