Investigation of the z,e isomerism of N-(5-pyrimidyl)- and N-(5-pyridyl) acetamidines

The processes of Z,E isomerization about the C=N bond and retardation of rotation about the C-N bond in N-(5-pyrimidyl)- and N-(5-pyridyl)-acetamidines were investigated on the basis of data on the temperature dependence of the PMR spectra. The effect of the type of heteroring, the volume of the ortho substituents, and the character of the solvents on the magnitude of the free energy of activation of Z,E isomerism was analyzed thoroughly. The possible mechanisms for the isomerization process are discussed.