Structure, vibrational assignment, and NMR spectroscopy of 1,2-bis (dichloroacetyl) cyclopentadiene

Molecular structure, intramolecular hydrogen bond (IHB), H-1 and C-13 chemical shifts, and vibrational assignment of newly prepared 1,2-bis (dichloroacetyl) cyclopentadiene (DCACP), have been investigated by means of density functional theory (DFT) calculations. In addition, the geometry of the most stable conformer was also optimized at the MP2/6-31G** level. By calculations at the B3LYP level, using 6-311++G** basis set, the IR band frequencies of the most stable conformer and its deuterated analogue and the C-13 and H-1 chemical shifts were clearly assigned. In addition, the anharmonic vibrational wave-numbers in solution were also calculated at the B3LYP/6-31G** level. All theoretical calculations and experimental spectroscopy data are consistent with a very strong intramolecular hydrogen bond in this zeta-diketone. According to the theoretical calculations, the enolated proton in DCACP slightly deviates from half way between the two oxygen atoms, C-s symmetry, which suggests existence of a low barrier double minimum potential for this system. (C) 2012 Elsevier B.V. All rights reserved.