4,6-Dimethoxy-3-methyldihydrotriazine-2-one (1) undergoes a single-crystal to single-crystal reversible phase transformation at 319 K. The low-temperature phase crystallizes in monoclinic space group P21/n with two crystallographically independent molecules in the asymmetric unit. The high-temperature phase is obtained by heating a single crystal of the low-temperature phase. This phase is orthorhombic, space group Pnma, with the molecules occupying a crystallographic mirror plane. The enthalpy of the transformation is 1.34 kJ mol−1. The small energy difference between the two phases and the minimal atomic movement facilitate the single-crystal to single-crystal reversible phase transformation with no destruction of the crystal lattice. On further heating, the high-temperature phase undergoes methyl rearrangement in the solid state. 2,4,6-Trimethoxy-1,3,5-triazine (3), on the other hand, undergoes an irreversible phase transformation from single-crystal to polycrystalline material at 340 K with an enthalpy of 3.9 kJ mol−1; upon further heating it melts and methyl rearrangement takes place.
4,6-Dimethoxy-3-methyldihydrotriazine-2-one (1) 在 319 K 下发生了单晶到单晶的可逆相变。低温相在单斜空间群 P21/n 中结晶,不对称单元中有两个晶体学上独立的分子。高温相是通过加热低温相的单晶体获得的。该相为正方晶系,空间群为 Pnma,分子占据一个晶体学镜面。转化焓为 1.34 kJ mol-1。两相之间的能量差很小,原子运动也很小,这有利于单晶到单晶的可逆相变,且不会破坏晶格。进一步加热时,高温相会在固态下发生甲基重排。另一方面,2,4,6-三甲氧基-1,3,5-三嗪(3)在开氏 340 度时发生了从单晶到多晶材料的不可逆相变,焓值为 3.9 kJ mol-1;进一步加热后,它熔化并发生甲基重排。