Topochemistry. Part XX. The crystal and molecular structures of dimethyl trans,trans-muconate

Abstract

The crystal and molecular structures of dimethyl trans,trans-muconate have been determined from three-dimensional counter data taken at room temperature with Cu K_α radiation and corrected for absorption. The structure was solved from a sharpened Patterson section and refined by a full-matrix programme with anisotropic temperature factors of the heavy atoms to r= 0·014 and R= 0·058. Secondary-extinction corrections reduced R to 0·046 but did not affect the atomic parameters. Analysis of the thermal vibrations suggests that the molecule vibrates as a rigid body. The bond lengths, before and after correction for thermal vibration, are: C–C 1·450, 1·454; CC 1·334, 1·341; CO 1·203, 1·218; COC–OCH₃ 1·338, 1·347; CO–CH₃ 1·445, 1·449 Å; the e.s.d.s. are 0·002 Å. The average length of the C–H bond is 0·96 Å. Analysis of the bond angles of the methoxycarbonyl group suggests that the axis of the methyl group makes an angle of 5° with the O–C vector; the effect is interpreted as evidence for a “bent” bond. The packing arrangement is discussed.