1-(Nitrosoamino)benzimidazoles Containing Electron-acceptor Substituents at the Amine Nitrogen. Theoretical and Experimental Investigation of Conformational Mobility

The previously unknown 1-(N-nitrosoallylamino)- and 1-(N-nitrosopropargylamino)benzimidazoles have been synthesized and they exist in solution as a mixture of the E- and Z-conformers due to hindered rotation around the N-N(O) bond. The activation energies for the EZ transition in these compounds and for the model N-benzyl analog have been determined by a dynamic ¹H NMR method. With a view to studying the effect of a substituent at the amino nitrogen on the EZ isomerization we have carried out 3-21G and 6-31G** type ab initio calculations of the stable conformers of a series of N-nitrosohydrazines.