Conformational Polymorphs of Acetone Tosylhydrazone

Two polymorphs of 2-isopropylidene-1-(p-toluenesulfono)hydrazide (acetone tosylhydrazone, C₁₀H₁₄N₂O₂S) are described. Both forms, one triclinic and the other monoclinic, are obtained upon crystallization from the same solvent. These are conformational polymorphs; the aryl ring eclipses one of the S-O bonds in the triclinic structure [O1-S1-C4-C5 - 0.9 (2)°] but not in the monoclinic structure [O1-S1-C4-C5 - 14.2 (2)°]. In spite of the conformational difference, molecules of the two polymorphs engage in similar intermolecular hydrogen-bonding contacts. Calculations using Cerius² [Molecular Simulations (1996). Cerius² Program. MS, 9685 Scranton Road, San Diego, CA 92121-3752, USA] indicate that the triclinic form is more stable than the monoclinic form by approximately 1 kcal. Subtle conformational differences of the type described here may be expected to present a challenge to the successful prediction of crystal structures.

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