Stable and metastable crystal phases of 4-methylbenzophenone

4-Methylbenzophenone crystallizes in a monoclinic stable form (mp 59°C) with a = 5.70 Å, b = 13.89 Å, c = 14.08 Å, β = 95.18° and space group P21/c, and a trigonal metastable form (mp 55°C) with a = 9.12 Å, c = 11.28 Å and space groups P31 or P32. The metastable phase is obtained only in highly supercooled melts at −25° to −35°C. It can undergo a monotropic phase transition into the stable form.