Hydrogen-bonding patterns in enaminones: (2Z)-1-(4-bromophenyl)-2-(pyrrolidin-2-ylidene)ethanone and its piperidin-2-ylidene and azepan-2-ylidene analogues

Abstract

The title compounds, namely (2Z)-1-(4-bromophenyl)-2-(pyrrolidin-2-ylidene)ethanone, C12H12BrNO, (I), (2Z)-1-(4-bromophenyl)-2-(piperidin-2-ylidene)ethanone, C13H14BrNO, (II), and (2Z)-2-(azepan-2-ylidene)-1-(4-bromophenyl)ethanone, C14H16BrNO, (III), are characterized by bifurcated intra- and intermolecular hydrogen bonding between the secondary amine and carbonyl groups. The former establishes a six-membered hydrogen-bonded ring, while the latter leads to the formation of centrosymmetric dimers. Weak C-H...Br interactions link the individual molecules into chains that run along the [011], [101] and [101] directions in (I)-(III), respectively. Additional weak Br...O, C-H...pi and C-H...O interactions further stabilize the crystal structures.