1,3,5-, 1,3,6-, 1,3,7-, and 1,3,8-Triazanaph thalenes

Some of the scatter within the groups is undoubtedly due to differences in bond order and also to whether or not the nitrogens are located in the same ring. Nevertheless, some striking exceptions are apparent in which the pA values are much higher than expected. These include quinazoline, 1,3,5-, 1,3,7-, 1,3,8-, and 1,4,6-triazanaph-thalene, pteridine, and 1,4,5,8-tetraazanaphthalene. In all these cases, covalent hydration of the cation has been shown to occur, so the measured pA values are, in fact, equilibrium values involving both hydrated and anhydrous species. The hydrated species are, without... 

Cations are more subject to ring-opening than are neutral species or anions. Thus ring-opening (slow) has been observed in the cations but not in the neutral species of 1,3,5-, 1,3,7-, and 1,3,8-triazanaph-thalene at 20° it is followed by further degradation. 1,3,6-Triaza-naphthalene decomposes much faster than its isomers in acidic solution, but follows the usual sequence, 47 49,... 

That resonance stabilization is just as essential as electron deficiency is shown by the anhydrous nature of both the neutral species and the cation of 4-nitroisoquinoline (40) and3-nitro-l,5-naphthyridine (41), for which hydration can cause no extra stabilization by resonance. These two substances are to be contrasted with equally electron-deficient substances which form strongly resonant hydrates, viz. quinazoline and 1,3,5-triazanaphthalene, respectively. No hydration could be detected in phthalazine or 8-methyl-l,6,7-triazanaph-thalene (a 5-azaphthalazine). ... 

---