The  tautomeric and structural properties of  5-hydroxy-2,2,6,6-tetramethyl-3-heptanone, (dipivaloylmethane,  C(CH3)3C(O)CH2C(O)C(CH3)3) have been studied by means of gas-phase  electron diffraction (GED) and quantum chemical calculations (B3LYP and MP2 approximation  with different basis sets up to aug-cc-pVTZ). Both, quantum chemistry and GED analyses resulted in the  presence of 100(5)% enol tautomer at 296(3)K. Quantum chemical calculations predict the existence  of two enol conformers in about equal amounts. In both conformers the enol ring possesses Cs  symmetry and they possess different torsional orientations of the two tert-butyl groups. The experimental  data refinement results in an enol tautomer, in which the tert-butyl group adjacent to the carbonyl group  possesses an intermediate orientation between those in “enol1” and “enol 2” forms (torsional angle  is about 30 ), and the tert-butyl group adjacent to the hydroxyl group slightly deviates from orientation  in the theore...
 
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