Absolute configuration and conformational stability of (S)-(+)-3-(2-methylbuthyl)thiophene and (+)-3,4-di[(S)-2-methylbutyl)]thiophene and their polymers

Enantiopure (+)-3-(2-methylbutyl)thiophene I and (+)-3,4-di(2-methylbutyl)thiophene II and their polymers were prepared using literature procedures and investigated using vibrational circular dichroism (VCD). Experimental absorption and VCD spectra of (+)-3-(2-methylbutyl)thiophene, (+)-3,4-di(2-methylbutyl)- thiophene, and their polymers in CDCl3 solution were recorded in the 2000-900 cm-1 region, and the experimental absorption and VCD spectra of (+)-3-(2-methylbutyl)thiophene were compared with the ab initio predictions of absorption and VCD spectra obtained with density functional theory using B3LYP/6- 31G* basis set for (S)-3-(2-methylbutyl)thiophene. This comparison indicates that (+)-3-(2-methylbutyl)- thiophene is of the (S) configuration and has six predominant conformations in CDCl3 solution and allows to securely distinguish the vibrational motions of the thiophene ring from those of the substituent moiety.