293. NMR spectroscopic and theoretical study on the isomerism of dimethyl benzodiazepine (diylidene)diacetates
The isomerism of dimethyl 2,2'-(7,8-dichloro-1H-benzo[b][1,4]diazepine-2,4-(3H,5H)diylidene)diacetate (1a) and dimethyl 2,2'-(7,8-dichloro-3-methyl-1H-benzo[b][1,4]diazepine-2,4-(3H,5H)diylidene)diacetate (1b) was investigated by 1H, 13C and 15N NMR spectroscopy. In CDCl3 solution, inversion of the diazepine ring was observed, whereas in (D6)DMSO and (D7)DMF solution, besides the ring inversion, a partial cleavage of one chelate ring appeared connected with (E/Z) isomerisation about one of the exocyclic C=C bonds. Gibbs free energies (ΔG) and Free activation energies (ΔG≠) were calculated based on B3PW91-SCRF/ZVP DFT computations. Agreement between NMR data and DFT computations was found.