Infrared spectra of substituted 5-phenyl-2-thiophenecarboxaldehydes and 2-(5-phenyl-2-thenylidene)-1,3-indandiones

Hammett correlations between the CO stretching frequencies and substituent constants were studied for a series of 5-phenyl-2-thiophenecarboxaldehydes and 2-(5-phenyl-2-thenylidene)-1,3-indandiones and compared with those for a series of benzaldehydes and 2-benzylidene-1,3-indandiones. From the slopes of the statistically most significant relationships the transmissive factors for the thiophene ring in carbon tetrachloride and chloroform were calculated. Transmission by the thiophene ring is practically independent of solvent contrary to transmission by the furan ring, where the transmissive center interacts with solvent molecules. From a comparison of transmissive factors it was found that the efficiency of transmission by the bridging groups decreases in the order furan > thiophene > benzene i.e. in the order in which the delocalization energies of these systems increase. The preparation of nine new 2-(5-phenyl-2-thenylidene)-1,3-indandiones is also described.