Geminal Diol Formation from the Interaction of a Ketone with Water in the Gas Phase: Structure and Reactivity of Cyclooctanone-(H₂O)_1,2 Clusters

Abstract

The hydration of ketones is known to occur in condensed phases, but it is not considered to be favorable in the gas phase due to restricted water content. We report the first evidence of geminal diol formation upon ketone hydration in the gas phase, obtained through the investigation of the interactions of cyclooctanone with water using broadband rotational spectroscopy. Oxygen-atom exchange between water and cyclooctanone was observed for two isomers of cyclooctanone-H 2 O and two isomers of cyclooctanone-(H 2 O) 2 . All complexes were unambiguously identified from the analysis of the rotational spectrum of the parent species and all their 13 C and 18 O isotopologues, and their heavy-atom substitution and effective structures were determined as well as their binding interactions. The production of gem-diols from gas-phase hydration of ketones has implications for atmospheric chemistry and opens a new channel for secondary aerosol formation.

Conformational Panorama of Cycloundecanone: A Rotational Spectroscopy Study

“…The structural and conformational data on CU presented here lay the groundwork for further studies of this ketone, for example, on their interactions with other molecules forming complexes or undergoing different reaction pathways . In this respect, cyclooctanone has been found to react with water, producing a geminal diol upon addition of one and two water molecules in the gas phase . Since CU is more reactive, it will be of interest to see if it undergoes a similar reaction forming a geminal diol upon hydration.…”

“…47 In this respect, cyclooctanone has been found to react with water, producing a geminal diol upon addition of one and two water molecules in the gas phase. 48 Since CU is more reactive, it will be of interest to see if it undergoes a similar reaction forming a geminal diol upon hydration.…”

Setting up the HyDRA blind challenge for the microhydration of organic molecules

“…As the energy balance between the two docking isomers could be subtle, we recommend to calculate both and to provide at least the donor OH stretching wavenumber of the more stable one. Note that there is isotopic exchange evidence for transient formation of the geminal diol from the ketone monohydrate, 59 but such a competing structural isomer should be easily distinguishable from the monohydrate complex also in the vibrational spectrum and is not the target for the present investigation. We are not aware of any vibrational study of the monohydrate of CON.…”

“…(e) Relative energy (in kJ mol À1 , excluding and including zero-point vibrational energy corrections) and spectral properties of any higher-lying conformations of the monohydrates which were investigated, within a range of 3-5 kJ mol À1 of the global minimum structure. Here, global is defined under the restriction that the chemical bond connectivity remains the same, so rearranged bonding patterns like geminal diols 59,97,98 as structural isomers of noncovalent ketone monohydrates 96 are not considered. Geometries, when available, may be provided.…”

“…58 The energy difference to the next conformation is so large that monohydration is unlikely to switch the energy sequence. Therefore up to two isomers of the monohydrate are expected 59 and the more stable one is of interest in the present challenge. As the energy balance between the two docking isomers could be subtle, we recommend to calculate both and to provide at least the donor OH stretching wavenumber of the more stable one.…”