rac-3-Benzoyl-2-methylpropionic acid and its organic salts: possibilities of Yang photocyclization in crystals.

The analysis of the crystal structures of rac-3-benzoyl-2-methylpropionic acid, C(11)H(12)O(3), (I), morpholinium rac-3-benzoyl-2-methylpropionate monohydrate, C(4)H(10)NO(+).C(11)H(11)O(3)(-).H(2)O, (II), pyridinium [hydrogen bis(rac-3-benzoyl-2-methylpropionate)], C(5)H(6)N(+).(H(+).2C(11)H(11)O(3)(-)), (III), and pyrrolidinium rac-3-benzoyl-2-methylpropionate rac-3-benzoyl-2-methylpropionic acid, C(4)H(10)N(+).C(11)H(11)O(3)(-).C(11)H(12)O(3), (IV), has enabled us to predict and understand the behaviour of these compounds in Yang photocyclization. Molecules containing the Ar-CO-C-C-CH fragment can undergo Yang photocyclization in solvents but they can be photoinert in the crystalline state. In the case of the compounds studied here, the long distances between the O atom of the carbonyl group and the gamma-H atom, and between the C atom of the carbonyl group and the gamma-C atom preclude Yang photocyclization in the crystals. Molecules of (I) are deprotonated in a different manner depending on the kind of organic base used. In the crystal structure of (III), strong centrosymmetric O...H...O hydrogen bonds are observed.