화학공학소재연구정보센터
Journal of Physical Chemistry A, Vol.112, No.14, 3209-3214, 2008
Tautomeric properties and gas-phase structure of 3-chloro-2,4-pentanedione
The tautomeric properties of a-chlorinated acetylacetone, 3-chloro-2,4-pentanedione CH3C(O)-CHCl-C(O)-CH3, have been investigated by gas electron diffraction (GED) and quantum chemical calculations (B3LYP and MP2 approximations with different basis sets up to cc-pVTZ). Analysis of the GED intensities resulted in the presence of 100(2)% enol tautomer at 269(8) K. The following skeletal geometric parameters (r(h1) values) of the molecule, which possesses C-s symmetry, were derived: r(C=C) 1.378(3) angstrom, r(C-C) 1.450(3) angstrom, r(C=O) = 1.243(3) angstrom, r(C-O) = 1.319(3) angstrom, r(O-H) = 1.001(4) r(C-Cl) = 1.752(4) angle C-C=C = 121.3(1.0)degrees, angle C=C-O = 119.9(1.2)degrees, angle C-C=O = 119.1(1.2)degrees. Due to very small contributions of the keto tautomer in alpha-chlorinated acetylacetone and its parent species, the effect of alpha-chlorination on tautomeric properties cannot be derived from experimental data. Quantum chemical calculations (B3LYP/ 6-31G**, B3LYP/cc-pVTZ, and MP2/cc-pVTZ) predict that alpha-chlorination of acetylacetone has no pronounced effect on the tautomeric properties. On the other hand, similar calculations for 1-chloro-1,3-butanedion, CIC(O)-CH2-C(O)CH3, demonstrate that chlorination in one beta position destabilizes the enol tautomer. In both chlorinated species the enol form is strongly preferred.