A comparative study of electric dipole moments of 2-substituted derivatives of furan, thiophen, selenophen, and tellurophen

Abstract

The electric dipole moments of tellurophen and some of its derivatives (tetrahydrotellurophen, nine 2-substituted and two 2,5-disubstituted) have been measured in benzene and compared with those of the corresponding derivatives of furan, thiophen, and selenophen, some of which (2-methylthio-furan and -selenophen, 2-acetylfuran, 2-methoxycarbonyl-furan and -selenophen and 2-NN-dimethylcarbamoyl derivatives) were not known. The mesomeric moments of the unsubstituted heteroaromatic congeners follow the ground state aromaticity order: thiophen > selenophen > tellurophen > furan. The mesomeric moments due to conjugation of the halogens with the heteroaromatic radical in the congener series are all greater than the benzene ones. The conformational problems of 2-methylthio-, 2-formyl, 2-acetyl, and 2-NN-dimethylcarbamoyl derivatives of tellurophen and its congeners have also been examined.