Results of the first extensive investigation of the nitrogen published work on solvent-induced effects on nitrogen shielding of 1,2,4,5-tetrazine ( I ) are reported. Due attention shieldings is 1,2,4,5-tetrazine: is paid to solvent-induced nitrogen-shielding variations by a variety of solvents. A comparison is made with comparable, earlier, results for the other azine systems. The observed range of solvent-induced nitrogen-shielding variations of I is modest but significant, about 10 ppm. The major factor producing this variation is that due to solvent polarity effects, which is supported by the results of some shielding calculations based upon the Solvaton model. A smaller, but significant, contribution is produced by solvent-to-solute hydrogen bonding effects. This correlates well with the low nitrogen basicity of I as indicated The only available nitrogen-shielding data for this tetrazine by published ab initio molecular orbital calculations of gas-(I) are from our early, low-precision, studies ( 3, 4). It is phase protonation energies. There is found a general corthe purpose of the present report to expand this earlier work relation between nitrogen basicity with respect to hydrogen on I to include some high-precision 14 N NMR measurements bonding and that with respect to protonation. GIAO / CHF niin a variety of solvents, the analysis of the results of these trogen-shielding calculations are reported for all of the existing measurements in terms of both specific and nonspecific solmonocyclic heteroaromatic azine systems including I using a ute-solvent interactions, and a study of protonation effects. 6-31 // G * * basis set. These appear to indicate that the inclusion of electron-correlation effects, reported for the SOLO
The protonation of compound I is of interest, since its method, does not result in a dramatic improvement in the calcubasicity as estimated by ab initio Hartree-Fock molecular lated nitrogen shieldings. α§ 1997 Academic Press orbital calculations for gas-phase protonation energies using a 6-31G* basis set is predicted to be the lowest in the azine series with the exception of the N 4 of 1,2,4-triazine (5). We