10.1021/jo060603e.s001 Natalya V. Belova Natalya V. Belova Georgiy V. Girichev Georgiy V. Girichev Sergey A. Shlykov Sergey A. Shlykov Heinz Oberhammer Heinz Oberhammer Tautomeric and Conformational Properties of Acetoacetamide:  Electron Diffraction and Quantum Chemical Study American Chemical Society 2006 set quantum chemical calculations CH 3C basis GED MP 2 approximations gas electron diffraction diketo Quantum Chemical StudyThe tautomeric properties quantum chemical method B 3LYP method enol 2006-07-07 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Tautomeric_and_Conformational_Properties_of_Acetoacetamide_Electron_Diffraction_and_Quantum_Chemical_Study/3072028 The tautomeric properties of acetoacetamide, CH<sub>3</sub>C(O)CH<sub>2</sub>C(O)NH<sub>2</sub>, have been investigated by gas electron diffraction (GED) and quantum chemical calculations (B3LYP and MP2 approximations with 6-31G(d,p) and 6-311++G(3df,pd) basis sets). GED results in a mixture of 63(7)% enol tautomer and 37(7)% diketo form at 74(5) °C. Only one enol form with the O−H bond adjacent to the methyl group (CH<sub>3</sub>C(OH)CHC(O)NH<sub>2</sub>) and only one diketo conformer (with dihedral angles τ(OC(CH<sub>3</sub>)CC) = 31.7(7.5)° and τ(OC(NH<sub>2</sub>)C(H<sub>2</sub>)C(O)) = 130.9(4.5)°) are present. The calculated tautomeric composition varies in a wide range depending on the quantum chemical method and basis set. Only the B3LYP method with small basis sets reproduces the experimental compositon correctly.