M. Schiavoni, H. Mack, C. Védova
Sep 27, 1996
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Journal
Journal of Molecular Structure
Abstract
Fourier transform infrared spectra and Raman spectra of malonyl chloride methyl and ethyl esters, ClC(O)CH2C(O)OCH3 and ClC(O)CH2C(O)OC2H5, in the liquid phase were analysed. These spectra reveal the existence of diketo conformers. The theoretical calculations for ClC(O)CH2C(O)OCH3 at the HF3–21G and HF6–31G∗∗ levels of the theory predict the existence of two stable diketo conformations. The lowest energy structure belongs to the C1 symmetry group with one C(O)Cl group rotated by δ1(O1C2C1C3) = −3.2° and the C(O)O group rotated by δ2(O2C3C1C2) = 104.7° from the CCC plane at the 6–31G∗∗ level of the theory. The second conformer, also with C1 symmetry, is about 0.6 kcal mol−1 higher in energy. The C(O)Cl group is rotated by δ1(O1C2C1C3) = 104.1° and the C(O)O group rotated by δ2(O2C3C1C2) = −10.2° from the CCC plane at the 6–31G∗∗ level of the theory. By comparison of the experimental results, the same behaviour is expected for the related molecule ClC(O)CH2C(O)OC2H5. The 1H NMR spectra of the two compounds evidence also that no enol tautomers are present in solution.