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trans-1,3-Bis(3,4-dimethoxyphenyl)-2,3-epoxy-1-propanone crystallizes in a monoclinic form (m.p. 155–156°C, from ethanol) and a trigonal form (m.p. 125–126°C, from chloroform/hexane or chloroform). NMR studies revealed that chloroform is present in the crystals of the trigonal form (epoxide/chloroform ratio ≈ 3:1). Solid-state NMR experiments showed that the trigonal form was gradually converted into the monoclinic form on storage in vacuo. On the basis of NMR and X-ray examinations it was concluded that the trigonal form is an inclusion compound of trans-1,3-bis(3,4-dimethoxyphenyl)-2,3-epoxy-1-propanone with chloroform. The crystal structure of the trigonal form with space group of R¯3, a = 36.0354(4), c = 8.2743(2) Å, and Z = 18, has been refined to R = 0.0506 by the employment of the SQUEEZE procedure implemented in PLATON-94.