Pyridazine, computational studies

The diazines pyridazine, pyrimidine, pyrazine, and their benzo derivatives cinnoline, phthalazine, quinazoline, quinoxaline, and phenazine once again played a central role in many investigations. Progress was made on the syntheses and reactions of these heterocycles, and their use as intermediates toward broader goals. Some studies relied on solid-phase, microwave irradiation, or metal-assisted synthetic approaches, while others focused attention more on the X-ray, computational, spectroscopic, and natural product and other biological aspects of these heterocycles. Reports with a common flavor have been grouped together whenever possible. 

A recent report from the U. K. deals with 1,4-bis(oxodihydropyridazin-yl)benzenes and congeners which are also potent phosphodiesterase inhibitors and inodilators [159], This investigation, together with computer-aided modelling studies on various phosphodiesterase III inhibitors [160], may well stimulate the rational design of additional pyridazine-derived inodilators. 

In this section we shall present and compare different computational strategies one can adopt to simulate the effect of the environment on spectroscopic properties of solvated systems. In particular, as a representative example, we shall summarize the results of two studies [30,31] we have published in the last years on the environment effects on the nitrogen nuclear shieldings of a specific class of molecular systems containing sp2-type nitrogens three diazines, also known as pyridazine (1,2-diazine), pyrimidine (1,3-diazine) and pyrazine (1,4-diazine). 

Pyridazine and its derivatives have been extensively studied by a variety of computational methods to correlate the predicted values of their physical properties with the measured ones. As for other azines also for pyridazine several methods were used to calculate its thermodynamic stability, molecular geometry, electron density distribution, ionization potentials, and dipole moments (89KGS1587 91RRC399) and the significance of different criteria for assessing the 77-electron delocalization were also reviewed (92H1631). 

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