Studies on Dithiocarbamates : Part X. Synthesis and Spectral Characteristics of Mesoionic 4-phenyl-5-aryl-1,3,4,-thiadiazoles

A series of the titled compounds have been synthesized with well-behaved meta and para-substituents on the phenyl ring at C₅ and their spectral data on long wavelength π→π* transition as well as the stretching frequency of C-S band have been examined in the light of linear free energy relationship. Thus, Hammett \(\sigma\rho\) relation was valid only with exalted values for NO₂ and CN groups indicating appreciable internuclear conjugation, comparable to biphenyl system, between the planar mesoionic ring and the phenyl ring at C₅. Strong dipolar interactions in solution have been demonstrated by the use of solvents of graded polarity.

In the UV region λmax around 275 and 250 m\(\mu\) have been assigned to phenyl groups at N₄ and C₅ respectively.