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Tautomeric and Conformational Properties of Acetoacetamide:  Electron Diffraction and Quantum Chemical Study

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journal contribution
posted on 2006-07-07, 00:00 authored by Natalya V. Belova, Georgiy V. Girichev, Sergey A. Shlykov, Heinz Oberhammer
The tautomeric properties of acetoacetamide, CH3C(O)CH2C(O)NH2, 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 (CH3C(OH)CHC(O)NH2) and only one diketo conformer (with dihedral angles τ(OC(CH3)CC) = 31.7(7.5)° and τ(OC(NH2)C(H2)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.

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