Structural and conformational study of substituted triazines by 1H and 13C NMR analysis

Two series of 2,4,6-tris(amino)-s-triazines were studied by 1H and 13C NMR. 15N NMR had previously demonstrated hindered rotation of the acyclic amino substituents (NHallyl, NHpropyl) around the Ar—N bonds at room temperature. In the present work, 1H and 13C NMR studies showed that rotation is hindered around the Ar—N bond for the secondary amino groups and also for the tertiary amino group. Furthermore, at low temperature the signals are differentiated for various sites of the amino substituents and for the carbons of the triazine as a function of interactions between groups in a meta position on the triazine. Thus the identification of the conformers is possible and a quantitative estimate of their contribution is obtained. Protonation at a nitrogen of the triazine leads to a highly predominant conformation which is characterized. The values of the free energies of activation for the rotation around the Ar—N bond and for the inversion of the piperazine ring were determined. Copyright © 2001 John Wiley & Sons, Ltd.