Tautomeric and conformational properties of dimethyl malonate, CH3OC(O)–CH2–C(O)OCH3: electron diffraction and quantum chemical study

The geometric structure of dimethyl malonate, CH3OC(O)–CH2–C(O)OCH3, was studied by gas electron diffraction (GED) and quantum chemical methods. We conclude that only diketo conformers exist in the gas phase. According to the GED refinement, a mixture of two diketo conformers is present: 69(10)% (ac,ac) conformer with C2 symmetry (both CyO bonds anticlinal relative to the opposite C–C bond) and 31(10)% (sp,ac) conformer with C1 symmetry (one CyO bond with synperiplanar, the other CyO bond with anticlinal orientation). Ab initio calculations, however, predict a preference of the (sp,ac) conformer rather than the (ac,ac) form. q 2003 Elsevier B.V. All rights reserved