Dihydro-1,2,4-triazines, stability tautomerism

Dihydro-1,3,5-triazines are of fundamental interest because of their ability to undergo amidinic tautomerism. Furthermore, as these are nitrogen-containing analogues of dihydropyrimidines (methylene at position 5 replaced by N) it would certainly be interesting to compare the effects of nitrogen substitution on the structual stability and tautomeric behavior of these compounds. 

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