4-Ethynyl-4-hydroxycyclohexan-1-one and 4-ethynyl-4-hydroxy-2,3,5, 6-tetramethylcyclohexa-2,5-dien-1-one.

The title compounds, C(8)H(10)O(2), (I), and C(12)H(14)O(2), (II), occurred as by-products in the controlled synthesis of a series of bis(gem-alkynols), prepared as part of an extensive study of synthon formation in simple gem-alkynol derivatives. The two 4-(gem-alkynol)-1-ones crystallize in space group P2(1)/c, (I) with Z' = 1 and (II) with Z' = 2. Both structures are dominated by O-H. O=C hydrogen bonds, which form simple chains in the cyclohexane derivative, (I), and centrosymmetric dimers, of both symmetry-independent molecules, in the cyclohexa-2,5-diene, (II). These strong synthons are further stabilized by C[triple-bond]C-H. O=C, C(methylene)-H.O(H) and C(methyl)-H.O(H) interactions. The direct intermolecular interactions between donors and acceptors in the gem-alkynol group, which characterize the bis(gem-alkynol) analogues of (I) and (II), are not present in the ketone derivatives studied here.