Chiral and Racemic Tetramorphs of 2,6-Di-t-Butylditolylfuchsone

The title molecule 4-(α,α-ditolylmethylene)-2,6-di- t -butyl-1,4-benzoquinone (abbreviated as di- t -butylditolylfuchsone and numbered 2- t -Bu) serendipitously afforded four concomitant polymorphs during routine purification by column chromatography in the same solvent elution fraction. Polymorph I crystallized in chiral space group P 2 1 . Polymorphs II, III, and IV crystallized in centrosymmetric space groups P 2 1 / n, Pbca, and C 2/ c, respectively. The role of bulky t -Bu groups for crystallization in the chiral space group is discussed for 2,6-ditolyl and 2,6-diphenyl fuchsones. α,α-Diphenylmethylene-2,6-di- t -butyl-1,4-benzoquinone (di- t -butyldiphenylfuchsone, 1- t -Bu) crystallized in P 2 1 (one polymorph) and P 2 1 / c (two polymorphs) space groups. Unfavorable steric repulsions due to bulky t -Bu groups result in voids in the crystal structures of centrosymmetric polymorphs II and III. Phase transformation of racemic structure II to III and finally to chiral polymorph I was monitored by thermal microscopy and differential scanning calorimetry. X-ray diffraction confirmed the phase transformation to be a single-crystal-to-single-crystal event. The chiral polymorph I is the stable modification in the tetramorphic system. Several randomly picked single crystals of 2- t -Bu polymorph I had the same absolute chirality by circular dichroism spectroscopy. A new molecule capable of exhibiting conformational chirality via atropisomerism is identified.