A Tetragonal-Looking But Twinned Orthorhombic Structure

2,2'-Methylenebis(3-hydroxy-5,5-dimethylcyclohex-2-en-1-one), C₁₇H₂₄O₄, forms crystals which appear tetragonal, but are actually orthorhombic. They are twinned on (110). The asymmetric unit consists of two very similar molecules, each with exact crystallographic C₂ symmetry. Each molecule forms two strong intramolecular hydrogen bonds connecting the two cyclohexenone rings.

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