Structure and conformational dynamics of an aromatic sulfonamide: NMR, X-Ray and computational studies

Two conformational diastereoisomers due to the hindered Aryl-NSO2 rotation were observed by NMR in the model compound N,N’-bis-tosyl-N,N’-dipropargyl-1,4-diamine-2,3-dimethyl benzene 1. X-Ray analysis showed that only the syn conformation is present in the solid state. The conformational preference in solution was evaluated by DFT calculations and experimentally determined by low-temperature NMR experiments. It was found that the anti conformation is the more populated in low-polarity solvents whereas the syn is the favored one in polar solvents