Collect. Czech. Chem. Commun. 1988, 53, 2366-2376

Conformational analysis by infrared linear dichroism of solutes in stretched polyethylene: The twist angle in biphenyl and 4,4'-dibromobiphenyl

Parvathi S. Murthy and Josef Michl

Department of Chemistry, University of Texas at Austin, Austin, TX 78712-1167, U.S.A.


A method is proposed for using the IR linear dichroism of molecules embedded in stretched polyethylene and containing two weakly coupled symmetry-related subunits for the determination of the spatial relationship of the subunits. The procedure requires an IR LD measurement on the parent and on an isotopomer in which the equivalence of the subunits has been removed by isotopic substitution, without affecting the molecular shape or the orientation factors. The method has been tested on biphenyl, found to be planar, and 4,4'-dibromobiphenyl, found to be nearly orthogonally twisted in stretched polyethylene. Possible implications for the orientation mechanism are discussed briefly.