Absolute Configuration and Conformational Stability of (S)-(+)-3-(2-Methylbutyl)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 CDCl 3 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 CDCl 3 solution and allows to securely distinguish the vibrational motions of the thiophene ring from those of the substituent moiety.