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

Molecular structure, intramolecular hydrogen bond (IHB), 1H and 13C 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 13C and 1H chemical shifts were clearly assigned. In addition, the anharmonic vibrational wavenumbers 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 ζ-diketone. According to the theoretical calculations, the enolated proton in DCACP slightly deviates from half way between the two oxygen atoms, Cs symmetry, which suggests existence of a low barrier double minimum potential for this system.

► bis(dichloroacetyl)cyclopentadiene forms strong intramolecular hydrogen bond.
► The potential function for proton movement is a low barrier double minimum.
► The OH stretching vibration is observed at about 1700 cm−1.
► The observed NMR chemical shifts are in agreement with the theoretical values.