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 (
![](/isubscribe/journals/jpcafh/111/i28/eqn/jp072122k<font color=)
e10001.gif"> -
![](/isubscribe/journals/jpcafh/111/i28/eqn/jp072122k<font color=)
e10002.gif">) 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 of
C2v 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(C=O) = 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,
![](/images/entities/ang.gif)
C-C=O = 119.9(2)
![](/images/entities/deg.gif)
,
![](/images/entities/ang.gif)
C-C-O = 111.0(2)
![](/images/entities/deg.gif)
,
![](/images/entities/ang.gif)
C-C-H = 108.2(7)
![](/images/entities/deg.gif)
,
![](/images/entities/ang.gif)
C-O-H = 106.5(7)
![](/images/entities/deg.gif)
. These structural parametersreproduce the experimental
![](/isubscribe/journals/jpcafh/111/i28/eqn/jp072122k<font color=)
e10003.gif"> values within 0.05 MHz. The experimental structural parameters are in goodagreement with those obtained from theoretical calculations. Ideal gas thermodynamic functions (
S![](/images/entities/deg.gif)
(
T),
![](/isubscribe/journals/jpcafh/111/i28/eqn/jp072122k<font color=)
e10004.gif"> and
H![](/images/entities/deg.gif)
(
T) -
H![](/images/entities/deg.gif)
(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.