(1)H, (13)C and (15)N NMR spectral assignments for new triazapentalene derivatives

Mesomeric heteropentalene betaines are conjugated fused polyheterocyclic structures that represent interesting intermediates for organic synthesis. Five such structures, containing at least four nitrogen atoms and various substituents, have been characterized by (1)H, (13)C and (15)N NMR. We report, apparently for the first time, nitrogen NMR data and coupling information on such systems. Inter-ring long-range correlations across five bonds with (15)N ((5)J(HN)) and up to seven bonds with (13)C ((6)J(HC) and (7)J(HC)) were observed in HSQC experiments. The incorporation of an electron-withdrawing substituent such as NO(2) was observed to cause an increase in the magnitude of the remote couplings and deshielding of nearby protons, carbons and on all nitrogen atoms of the structure, including remote ones situated on other cycles.