Several conformers of the bioactive Morita-Baylis-Hillman adducts (MBHA) 1-4 were studied. Relaxed potential energy surfaces scan (RPESS) have been performed. The principal structures obtained from RPESS approach were then fully optimized at B3LYP/6-311++G** level and with PCM model simulating water media at B3LYP/6-31+G* level. The relative stabilities obtained for conformers 1, 2 and 4 in gas and water media are different. Six and seven member intramolecular hydrogen bonds (IHBs) have been characterized for adducts I and 4, respectively, through atoms in molecules (AIM) calculations. The occurrence of such type of IHBs was also supported by IR and H-1 NMR spectroscopic data. (C) 2007 Elsevier B.V. All rights reserved.