1H and 13C nuclear magnetic resonance study of 1,3‐dipyridylthioureas for chemical shift assignments and conformational analysis

Abstract

AbstractA study of molecular conformation by 1H and 13C NMR methods of three 1,3‐dipyridyl thioureas namely, 1,3‐di(2‐pyridyl)thiourea (1), 1,3‐di(3‐pyridyl)thiourea (2), 1‐(2‐pyridyl)‐3‐(3‐pyridyl)thiourea (3), and also of 1‐phenyl‐3‐(2‐pyridyl)thiourea (4) and 1,3‐diphenylthiourea (5), included for the sake of comparison, was carried out. Evidence was obtained that 3 and 4 exist in solution solely in one form, in an internally hydrogen bonded E,Z conformation, whereas 1, 2 and 5 exist in two (or more) rotamer forms. The data reveal an interesting dynamic exchange phenomenon occurring in 1 between two intramolecularly hydrogen bonded conformers. The 1H and 13C chemical shifts, 1H,1H and 13C,1H coupling constants are reported. The 13C and 1H chemical shifts are correlated with the electron densities calculated by the CNDO method.