| Abstract
| - The molecular structure of 1,3-dihydroxyacetone (DHA) has been studied by gas-phase electron diffraction(GED), combined analysis of GED and microwave (MW) data, ab initio, and density functional theorycalculations. The equilibrium re structure of DHA was determined by a joint analysis of the GED data androtational constants taken from the literature. The anharmonic vibrational corrections to the internuclear distances(re − ra) and to the rotational constants (−) needed for the estimation of the re structure werecalculated from the B3LYP/cc-pVTZ cubic force field. It was found that the experimental data are wellreproduced by assuming that DHA consists of a mixture of three conformers. The most stable conformer ofC2v symmetry has two hydrogen bonds, whereas the next two lowest energy conformers (Cs and C1 symmetry)have one hydrogen bond and their abundance is about 30% in total. A combined analysis of GED and MWdata led to the following equilibrium structural parameters (re) of the most abundant conformer of DHA (theuncertainties in parentheses are 3 times the standard deviations): r(CO) = 1.215(2) Å, r(C−C) = 1.516(2)Å, r(C−O) = 1.393(2) Å, r(C−H) = 1.096(4) Å, r(O−H) = 0.967(4) Å, ∠C−CO = 119.9(2)°,∠C−C−O = 111.0(2)°, ∠C−C−H = 108.2(7)°, ∠C−O−H = 106.5(7)°. These structural parametersreproduce the experimentalvalues within 0.05 MHz. The experimental structural parameters are in goodagreement with those obtained from theoretical calculations. Ideal gas thermodynamic functions (S°(T),and H°(T) − H°(0)) of DHA were calculated on the basis of experimental and theoretical molecularparameters obtained in this work. The enthalpy of formation of DHA, −523 ± 4 kJ/mol, was calculated bythe atomization procedure using the G3X method.
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