Didehydropyrazines

Didehydropyrazine is believed to be an intermediate in the pyrolysis of pyrazine-2,3-dicarboxylic anhydride. According to DFT calculations, this molecule has a triplet ground state with a singlet state about 10 kcal/mol higher in... 

Fine structures. Di- and tetradehydropyrazines (as their derivatives) are sometimes implicated as transient intermediates in proposed reaction mechanisms. Some theoretical studies have suggested that didehydropyrazine would exist as the diradical structure (3),454 whereas others seem to suggest more normal formulations for di- (4) and tetradehydropyrazine (5).235... 

SemiempiricaP and ab initio calculations have been carried out on didehydro-pyridazines 766 and 767, didehydropyrimidine 768 and didehydropyrazine 769. These calculations predict that 766 is more stable than 767 by 11-12 kcal mol for reasons similar to those for the greater stability of 2 over 717. This result is in accord with the considerably greater experimental evidence for 766 compared with 767 . Although a large diradical character was claimed for 769 this conclusion was not substantiated by the ab initio calculations, nor by a recalculation of the semiempirical resulP. ... 

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