Molecular Packing Modes. Part X. The Crystal and Molecular Structures of Trans, Trans‐Muconic Acid

trans, trans‐Muconic acid C₆H₆O₄ crystallises in the space group (Formula Presented.) , with a = 8.982, b = 9.895, c = 3.787 Å, α = 103.68, β=75.27, γ= 101.58°, and two centrosymmetric molecules per unit cell. The structure was solved from 1671 reflections measured by an ω/2θ scan with Mo Kα radiation on an IBM 1800 computer‐controlled Siemens diffractometer, and refined anisotropically (on F²) to R = 0.078. The geometries in the carbon chains of the two independent molecules are essentially identical; their bond lengths match to within 0.003 Å. The carboxyl group of one molecule is statistically disordered (C‐O 1.257, 1.275 Å) whereas in the second molecule the bond lengths differ significantly (1.236, 1.294 Å), indicating a greater degree of order. A careful consideration of the packing mode allows us to interpret the difference between the two molecules.