RELATIVE STABILITY AND STRUCTURE OF DIHYDRO-1,2,4-TRIAZINES - A THEORETICAL-STUDY

A brief survey is given on the synthesis and structure elucidation for dihydro-1,2,4-triazines. The relative stability of nine possible dihy dro-1,2,4-triazines and three dihydrotriazinium cations is studied at HF, MP2, generalized gradient approximation DFT, and CBS-4 levels of t heory. The structural consequences of the inclusion of the electron co rrelation are also given. We attempt to rationalize the experimental f indings using high-quality theoretical results. The quantum chemical c alculations support that the most stable isomer is the 2,5-dihydro-1,2 ,4-triazine and all the other relatively stable isomers have been expe rimentally identified correctly. Several experimental papers report st ructures that have been proved to be nonexistent. These structures hav e energy that is too high according to the best-quality calculations.