Matrix-Isolation Study and Ab Initio Calculations of the Structure and Spectra of Hydroxyacetone

Abstract

The structure of hydroxyacetone (HA) isolated in an argon matrix (at 12 K) and in a neat solid phase (at 12-175 K) was characterized by using infrared (IR) spectroscopy. The interpretation of the experimental results was supported by high-level quantum chemical calculations, undertaken by using both ab initio (MP2) and density functional theory methods. A potential-energy surface scan, carried out at the MP2/6-311++G(d,p) level of theory, predicted four nonequivalent minima, Cc, Tt, Tg, and Ct, all of them doubly degenerate by symmetry. The energy barriers for conversion between most of the symmetrically related structures and also between some of the nonequivalent minima (e.g., Tg --> Tt and Ct --> Tt) are very small and stay below the zero-point vibrational level associated with the isomerization coordinate in the higher-energy form in each pair. Therefore, only Cc and Tt conformers have physical significance, with populations of 99 and 1%, respectively, in gas phase at room temperature. For the matrix-isolated compound, only the most stable Cc conformer was observed. On the other hand, the polarizable continuum model calculations indicated that in water solution, the population of Tt and Ct conformers might be high enough (ca. 6 and 11%, respectively) to enable their experimental detection, thus supporting the conclusions of a previous IR spectroscopy study [ Spectrochim. Acta A 2005, 61, 477] in which the presence of more than one HA conformer in aqueous solution was postulated. The signatures of these minor conformers, however, do not appear in the spectra of the neat HA crystal, and the crystal structure was rationalized in terms of centrosymmetric hydrogen-bonded dimers consisting of two Cc-like units. Finally, we calculated (1)H, (13)C, and (17)O NMR chemical shifts at different levels of theory and found them to agree with available experimental data.

In situ direct photoproduction of ketenes from substituted coumarins isolated in solid argon: The case of N-(2-oxo-2H-chromen-3-yl)acetamide

“…A similar small geometric distortion in the CH 3 AC(@O) moiety from the symmetric C s geometry was recently reported for hydroxyacetone [31]. As found for hydroxyacetone [31], the energy difference between the C s structure and the two symmetrically equivalent minima it separates stays below the zero-point vibrational level of these later, which means that in practical terms the relevant (most probable) structure is the symmetric one. In conformers II and III, the planes of the coumarin and acetamide fragments make angles (C4@C3AN12AC19) of 14.5°and 128.2°, respectively.…”

Conformational Switching Induced by Near-Infrared Laser Irradiation

“…3 Atmospheric HA reacts with an OH radical under sunlight irradiation 4 and also contributes to the formation of secondary organic aerosols. 5 The overall rate coefficient for the tropospherically relevant reaction, HA+OH, was proposed 6 to depend on the initial conformation of the HA molecule.Theoretical calculations on HA monomers in the gas phase 7,8 show that there are only two conformers (Cc and Tt) of this compound ( Figure 1). The lowest energy conformer of HA is Cc, whereas Tt was predicted to be higher in energy by 994 cm -1 .…”

“…Theoretical calculations on HA monomers in the gas phase 7,8 show that there are only two conformers (Cc and Tt) of this compound ( Figure 1). The lowest energy conformer of HA is Cc, whereas Tt was predicted to be higher in energy by 994 cm -1 .…”

“…Hence, the Cc conformer should represent 99% of the conformational equilibrium at room temperature, 8 which is why only the Cc conformer has been observed so far. 2,8,9 In this work, we report the first experimental observation of the elusive high-energy Tt conformer of hydroxyacetone. We show that, for HA isolated in a low-temperature Ar matrix, the Tt conformer can be produced by narrow-band near-infrared (NIR) vibrational excitation of the conformational ground state Cc.…”

Proton transfer reactions between nitric acid and acetone, hydroxyacetone, acetaldehyde and benzaldehyde in the solid phase

“…35 for acetone, ref. 36 for hydroxyacetone, and ref. [37][38][39] for acetaldehyde), and the difference spectra of the bulk nitrates at saturation (scaled for display).…”