Pyrazine 1.4- dihydro-, antiaromatic

Pyrazine, 2,5-dichloro-3,6-difluoro-synthesis, 3, 190-191 Pyrazine, dihydro-, 3, 177 Pyrazine, 1,2-dihydro-oxidation, 3, 178 reduction, 3, 177 Pyrazine, 1,4-dihydro-antiaromaticity, 3, 177-178 synthesis, 3, 177 Pyrazine, 2,3-dihydro-oxidation, 3, 178 Pyrazine, 2,5-dihydro-synthesis, 3, 178 Pyrazine, 3,6-dihydro-synthesis, 3, 184 Pyrazine, 2,5-dihydroxy-oxidation, 3, 175 Pyrazine, 2,3-dimethyl-1,4-dioxide... 

As true reduced flavins , however, and apart from flavohydroquinone, one example of each subclass needs discussion, viz. 4a,5-dihydro-flavin( 5-blocked ) 181,182)and l,8-dihydroflavin( l/2a-blocked ) 12). Both isomers exhibit chromophores which are essentially different from flavohydroquinone, as outlined in Scheme 9. The three dihydro isomers exhibit, furthermore, totally different chemical reactivity 1,8-dihydro-flavin is aromatic with respect to electron distribution in the center (pyrazine) subnucleus, 1,5-dihydroflavin is, contrarily, antiaromatic (unless the pyrazine subnucleus is deplanarized, see below). It contains... 

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