The structures of acetylacetone,trifluoroacetyl-acetone and trifluoroacetone |
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Authors: | AL AndreassenSH Bauer |
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Institution: | Department of Chemistry, Cornell University, Ithaca, N.Y. 14850 U.S.A. |
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Abstract: | The molecular geometries of three structurally related compounds have been determined by electron diffraction in the gas phase. Acetylacetone, which exists primarily as the enol tautomer, was found to have a planar symmetric ring with the following rg values: C1-C2 = 1.405± 0.005 Å, C2-C4 = 1.510± 0.005 Å, C-O = 1.287± 0.006 Å, C-H = 1.090± 0.010 Å, ∠C2C1C3 = 118.3 ± 1.8°, ∠C1C3O1 = 123.2± 1.7°, ∠C1C3C5 = 122.0± 1.2°, and ∠CCH = 110.2 ± 2.1°. A model in which the enol proton is in the ring plane located symmetrically between the oxygen atoms is in best agreement with the diffraction data. The structure of trifluoroacetylacetone is similar to that of acetylacetone. The rg values for this compound are C1-C3 = 1.4164 ± 0.006 Å, C3-C5 = 1.511 ± 0.021 Å, C2-C4 = 1.536 ± 0.018 Å, C-O = 1.270 ± 0.008 Å, C-H = 1.088 ± 0.039 Å, C-F = 1.340 ± 0.005 Å, ∠C2C1C3 = 117.2 ± 1.8°, ∠C1C2O2 = 123.6 ± 1.7°, ∠C1C3C5 = 118.1 ± 2.3°, ∠C1C2C4 = 123.0 ± 1.4°, ∠CCH = 109.0± 4.8°, and ∠CCF = 110.6± 0.8°. The rg values for the trifluoroacetone are: C1-C2 = 1.481 ± 0.019 Å, C1-C3 = 1.562 ± 0.011 Å, CO = 1.207 ± 0.006 Å, C-H = 1.089 ± 0.024 Å, C-F = 1.339 ± 0.003 Å, ∠C2C1O = 122.0 ± 1.1°, ∠C3C1O = 116.8 ± 0.7 °, ∠CCH = 105.0 ± 2.2 °, and ∠CCF = 110.7 ± 0.3°. The significance of the error estimates is discussed briefly. |
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