1,l0-Phenanthroline-5,6-quinone is prepared from 1,l0-phenanthroline via 5-nitro-1,l0-phenanthroline and 5-amino-1,l0-phenanthroline. It is converted by standard methods into 4,5-diazafluoren-9-one, 4,5-diazafluoren-9-ol,4,5-diazafluorene, and the new heterocyclic system dipyrido[3,2-a:2',3'-clphenazine. These four compounds each form a complex with cupric chloride. They thus represent a new series of chelating agents. By reaction with ethylene dibromide, dipyrido[3,2-a:2',3'-c]-phenaiine forms a diquaternary salt which is reduced in aqueous solution by a one-electron transfer to a highly coloured radical cation. Polarography experiments show that the reduction potential of the salt is -0.40 V against a standard calomel electrode.

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N.m.r. spectral studies demonstrated that Meisenheimer salts were formed by addition of alkali metal methoxides to 4-cyano-2,6-dinitroanisole, 4-methoxy-3,5-dinitropyridine, and 2,6-dinitroanisole, but not with 2-methoxypyrimidine. Crystalline salts were isolated after addition of methoxide to the cyanodinitroanisole and methoxydinitropyridine. The stabilities of the Meisenheimer salts were found to be heavily dependent on the ability of ring substituents to accept negative charge.