Raman spectroscopy, surface‐enhanced Raman spectroscopy and density functional theory studies of 2‐formylfuran

Abstract

AbstractThe Raman spectrum of 2‐formylfuran in the liquid phase shows pairs of bands whose temperature and solvent dependence behavior can be interpreted in terms of cis–trans conformational equilibrium. Density functional theory (DFT) calculations performed at the BPW91/6–311+G* and B3LYP/6–311+G* theoretical levels show that the trans‐isomer is more stable than the cis‐isomer by 2.81 and 3.12 kJ mol−1, respectively. The theoretical ΔH values obtained at these theoretical levels [2.99 kJ mol−1 (BPW91) and 3.2 kJ mol−1 (B3LYP)] are very close to the experimental value ΔH = 2.52 kJ mol−1 determined from the plots of logarithmic relative intensities of the band pairs 1673/1692, 1477/1465 and 1396/1371 cm−1 of these isomers against reciprocal temperature. The surface‐enhanced Raman spectrum of 2‐formylfuran in silver colloid suggests the chemisorption of this molecular species on the silver surface both through the ring oxygen and the oxygen atom of the substituent group, the cis‐form being preferred in the adsorption state. The adsorbed molecules are oriented perpendicular or least tilted with respect to the silver surface. Copyright © 2003 John Wiley & Sons, Ltd.