THEORETICAL-ANALYSIS OF COMPETITIVE DIRECTIONS OF ELECTROCYCLIZATION OF 3,4,6-TRIAZAOCTA-1,3,5,7-TETRAENE - INVESTIGATION OF THE STRUCTURE AND ELECTROCYCLIZATION OF 1,2,4-TRIAZAHEXA-1,3,5-TRIENE

Theoretical analysis of competing directions of electrocyclization of triazatetraene H2C=CH-N=N-CH=N-CH=CH2, triazatrienes H2C=CH-N=N-CH=NH and HN=N-CH=N-CH=CH2, and 1,4-diphenyl-1,2,4-triazabuta-1,3-diene Ph-N =N-C(R)=N-Ph was carried out. Specific features of cyclization of thes e compounds were explained by differences in the energies of pi-orbita ls of C=C, C=N, and N=N bonds and in bond order; of atoms forming a ne w bond in the reaction. The activation barrier and the structure of th e transition state of the electrocyclization of 1,2,4-triazahexa-1,3,5 -triene were studied by AM1, MNDO, and MINDO/3 methods. The electrocyc lization of triazatriene is an asymmetric disrotatory process. The rot ation angle of the terminal CH2 group around the C=C bonds is twice as large as that of the NH group around the N=N bond. The 1,3-prototropi c shift in dihydro-1,2,4-triazines is discussed.