Z,E isomerism and hindered rotations in malonamides: an NMR study of N,N '-dimethyl-N,N '-dibutyl-2-tetradecylpropane-1,3-diamide

The title propane-1,3-diamide has three geometrical isomers, ZZ, ZE and EE, in slow exchange on the NMR timescale. The distribution of isomers involve s the two amide moieties in a statistical manner. Four types of conformatio nal changes ZZ reversible arrow ZE reversible arrow EE are shown by exchang e correlation spectroscopy and lineshape calculations. Isomers are identifi ed on the basis of aromatic solvent induced shift (ASIS) and lanthanide ind uced shift (LIS) experiments. Barriers to rotation in each amide moiety are relatively low due to the bulkiness of N- and C-substituents, typically 71 kJ mol(-1) at 25 degrees C, and are weakly sensitive to the conformational state (Z or E) of the other amide moiety.