Contrasting Effects of Water on the Barriers to Decarboxylation of Two Oxalic Acid Monohydrates: A Combined Rotational Spectroscopic and Ab Initio Study

Water binding to the atmospheric oxidation product methyl vinyl ketone

Methyl vinyl ketone is one of the major oxidation products of isoprene, and therefore, an important precursor of secondary organic aerosol. Understanding its interactions with water is relevant to gain insight into aerosol formation and improve the predictive power of atmospheric chemistry models. The molecular complex formed between methyl vinyl ketone and water has been generated in a supersonic jet and characterized using high-resolution microwave spectroscopy in combination with quantum chemistry calculations. In this study, we show that methyl vinyl ketone interacts with water forming four 1:1 isomers connected by O - H···O and C - H···O hydrogen bond interactions. Water has been found to preferentially bind to the antiperiplanar conformation of methyl vinyl ketone. Evidence of a large amplitude motion arising from the methyl internal rotation has been found in the rotational spectra of the dimer. The threefold methyl internal rotation barrier heights have been further determined and discussed for all the species.

Interactions of limonene with the water dimer

The interactions of limonene with the water dimer have been characterised through the identification of seven different isomers.

Geminal Diol Formation from the Interaction of a Ketone with Water in the Gas Phase: Structure and Reactivity of Cyclooctanone-(H2O)1,2 Clusters

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-H₂O and two isomers of cyclooctanone-(H₂O)₂. All complexes were unambiguously identified from the analysis of the rotational spectrum of the parent species and all their ¹³C and ¹⁸O 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.

New Insights into Secondary Organic Aerosol Formation: Water Binding to Limonene

Limonene is an abundant monoterpene in the atmosphere and one of the main precursors of secondary organic aerosol. Understanding its interactions with atmospheric molecules is crucial to explain aerosol formation and the various products obtained from competing reaction pathways. Here, using broadband rotational spectroscopy in combination with computational calculations, we show that limonene effectively interacts with water, forming a variety of complexes. Seven different isomers of limonene-H₂O, where water and limonene are connected by O-H···π and C-H···O interactions, have been unambiguously identified. Water has been found to preferentially bind to the endocyclic double bond of limonene. Our findings demonstrate a striking ability of water to attach to limonene and enrich our knowledge on the possible interactions of limonene in the atmosphere.

Conformation and bonding of 2-methoxypyridine and its monohydrate from rotational spectra

Rotational spectra of 2-methoxypyridine and its monohydrate have been characterized by pulsed jet Fourier transform microwave spectroscopy and complementary ab initio calculations. Rotational spectra of the parent monomer and seven mono-substituted isotopologues (¹³C and ¹⁵N) were measured in natural abundance, which allow determining the accurate structure of the skeleton of 2-methyoxypyridine. The barrier to the methyl internal rotation was determined from the A/E torsional symmetry species of the rotational transitions. For the 2-methyoxypyridine⋯H₂O complex, rotational spectra of the parent dimer and isotopologues formed with isotopically enriched water (H₂¹⁸O, HOD, DOH and D₂O) indicate that the observed isomer is stabilized by a strong OH⋯N and a secondary bifurcated (CH)₂⋯O weak hydrogen bonds. Bader's quantum theory of atoms in molecules and Johnson's non-covalent interaction analyses were applied and visualized to have a better understanding of the non-covalent interactions in 2-methyoxypyridine⋯H₂O.

Water Docking Bias in [4]Helicene

We report on the one- and two-water clusters of [4]helicene, the smallest polycyclic aromatic hydrocarbon with a helical sense, which were captured in the gas phase using high-resolution rotational spectroscopy. The structures of the complexes are unambiguously revealed using microwave spectra of isotopically enriched species. In the one-water cluster, the apparent splitting pattern is consistent with a tunneling motion that encompasses an exchange of strongly and weakly bonded water hydrogens. This motion is "locked" in the two-water cluster. The relevant intermolecular contacts, symmetry, and aromaticity effects are unveiled for the microsolvated chiral topologies. These observations entail the first glance at the structures and internal dynamics of the water binding motifs of a chiral polycyclic aromatic hydrocarbon.

Hydration of the simplest α-keto acid: a rotational spectroscopic and ab initio study of the pyruvic acid–water complex

Non-covalent interactions analysis of hydrogen bonding in the pyruvic acid water complex.

Tunnelling and barrier-less motions in the 2-fluoroethanol–water complex: a rotational spectroscopic and ab initio study

Rotational spectrum of 2-fluoroethanol–water reveals interesting water and methyl internal rotation tunneling and barrier-less motions in the hydrogen-bonded complex.