Abstract
Resonance Raman spectra reveal that 3-alkyl-substituted 1,5-diphenylformazans exist as one of the following three isomeric species in the solid state: the yellow isomer has the trans- anti-s- trans configuration with respect to the NN, CN and CN bonds of the formazan skeleton, the red isomer has the trans- syn-s- trans configuration and the other red isomer has the trans- syn-s- cis configuration. The relative stabilities of these isomers are determined by the bulkiness of the substituent. When the substituent is small, the fully extended trans- anti-s- trans configuration is most stable. However, when the substituent is large, the partially folded trans- syn-s- trans configuration becomes stable and when the substituent is very bulky, the more folded trans- syn-s cis configuration is most stable. In solution these isomers are in equilibrium, the relative abundance being dependent on the nature of the solvent as well as on the bulkiness of the substituent.
Published Version
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