C-13 NMR INVESTIGATION OF 2,5-DIARYL-1,4-DITHIINS

The 13C NMR spectra of eight 2,5‐diaryl‐1,4‐dithiins were recorded and signals were assigned. A linear correlation was observed between the electronegativity of the substituent groups on C‐10,10′ and the chemical shifts of C‐10,10′ after applying corrections for the magnetic anisotropic effect of the substituents. A Hammett correlation was found between the 13C chemical shifts of C‐3,6 and C‐7,7′ and the σp+ parameter associated with the substituents on C‐10,10′. Extended electronic interaction between the π system of the aryl group and the π system of the dithiin ring was suggested by the observance of an alternating behavior in the magnitude of the substituent effects on the 13C shifts of C‐2,5 and C‐3,6. An alternating effect was also noted in the magnitude of the long‐range 13CF coupling constants for these same carbon signals in 2,5‐(10,10′‐difluoro)diphenyl‐1,4‐dithiin. Copyright © 1979 Heyden & Son Ltd.