Conformational properties of 3,3'-, 3,4'- and 4,4'-dimethyl- and -bis(methylsulfanyl)-2,2'-bithiophenes

The conformational properties of the title compounds, which are the basic head-to-head, head-to-tail and tail-to-tail repeat units of regioregular poly(3-methylthiophenes) and poly[3-(methylsulfanyl)thiophenes], are discussed. The paper reports the X-ray structures of the two 4,4?-derivatives, 1H NMR NOE data on the 3,4? and 4,4?-derivatives and force field MM2 calculations of the conformation of the three bis(methylsulfanyl) derivatives.