4-Benzylideneamino-1, 2, 4-triazine-3, 5 (2H, 4H)-diones (2–5), 6-styryl-1, 2, 4-triazine-3, 5 (2H, 4H)-dione (6), and 6-styryl-2, 3-dihydro-3-thioxo-1, 2, 4-triazin-5 (4H)-one (7) were synthesized and pyrolyzed in the gas phase. The kinetic effect of changing the substituent on the triazine ring from hydrogen to methyl, phenyl, and styryl was measured. Analyses of the pyrolyzates of 2–5 showed the elimination products to be benzonitrile and the triazine ...