有机化学问题，是否存在2，4，6，三硝基1，3，5，三嗪，如图，若不存在，理由

命名时没问题的。
英文wiki是这么说的：
Trinitrotriazine, or 2,4,6-trinitro-1,3,5-triazine, is a theoretical explosive compound. Synthesis of this compound has been elusive despite its simple structure, as conventional nitration of triazine becomes increasingly more difficult as more nitro groups are added. A successful route would more likely proceed by trimerisation of nitryl cyanide, but this precursor also has not yet been synthesised.
It has a perfect oxygen balance, potentially making it a very powerful explosive, though calculations predict it would be fairly unstable and inferior to the related compound 3,6-dinitro-1,2,4,5-tetrazine.
大概意思就是这是一个理论上很强的爆炸物，不稳定，很难合成。
我自己也稍微查了一下，没发现有报导的合成路线。

不存在，要从有取代基的位置开始计数