Moriguchi, K; Kamata, T; Harimoto, T; Matsumoto, Y; Nakashima, H; ,
Conformational analysis of stereoisomers of 1-phenyl-4-(1'-phenylethyl)-tetralin (1,4-PPET) and 1,3,5-triphenylcyclohexane (1,3,5-TPCH) were investigated using H-1 and C-13 nuclear magnetic resonance (NMR) spectroscopy, among several styrene trimers that remained in polystyrene products for food containers. Four stereoisomers of 1,4-PPET were isolated from a mixture of styrene oligomers formed during the thermal polymerization of styrene by employing a recycling method of preparative high-performance liquid chromatograph!, (preparative HPLC). As for 1,3,5-TPCH, two kinds of stereoisomers were obtained by means of two kinds of synthetic methods with different steroselectivities. We confirmed that the four stereoisomers of 1,4-PPET are (1-eq, 4-eq), (l-ax, 4-eq), (l-ax, 4-ax) and (1-eq, 4-ax) conformers (ax: axial, eq: equtorial), in order of their gas-chromatographic (GC) elutions, respectively, based on the relationships of the vicinal coupling constants of tetralin protons. This result was also supported by the H-1 and C-13 NMR chemical shifts (delta(H), delta(C)) of 1', 2'(CH3) protons and 2'(CH3) carbon. As for 1,3,5-TPCH, we obtained (Irans, cis) and (cis, cis) isomers as two kinds of stereoisomers in order of their GC elutions using two kinds of synthetic methods with different stereoselectivities, and concluded that they were (1-ax, 3-eq, 5-eq) and (1-eq, 3-eq, 5-eq) conformers, respectively, based on the relationship among the typical coupling constants of cyclohexane protons and the corresponding H-1 and C-13 NMR chemical shifts of the cyclohexane rings. The characterization of the conformation of styrene trimers seems to be significant for future investigations of endocrine-disrupting mechanisms.