Wetting vs Droplet Aggregation: A Broadband Rotational Spectroscopic Study of 3‐Methylcatechol⋅⋅⋅Water Clusters

Abstract

Two competing solvation pathways of 3‐methylcatechol (MC), an atmospherically relevant aromatic molecule, with up to five water molecules were explored in detail by using a combination of broadband rotational spectroscopy and computational chemistry. Theoretically, two different pathways of solvation emerge: the commonly observed droplet pathway which involves preferential binding among the water molecules while the solute serves as an anchor point for the formation of a water cluster, and an unexpected wetting pathway which involves interactions between the water molecules and the aromatic face of MC, i.e., a wetting of the π‐surface. Conclusive identification of the MC hydrate structures, and therefore the wetting pathway, was facilitated by rotational spectra of the parent MC hydrates and several H218O and 13C isotopologues which exhibit splittings associated with methyl internal rotation and/or water tunneling motions. Theoretical modelling and analyses offer insights into the tunneling and conversion barriers associated with the observed hydrate conformers and the nature of the non‐covalent interactions involved in choosing the unusual wetting pathway.

Water Arrangements upon Interaction with a Rigid Solute: Multiconfigurational Fenchone-(H2O)4–7Hydrates

“… However, a prism-like structure is preferred for glycolaldehyde-(H 2 O) 6 and 3-methyl-3-oxetanemethanol-(H 2 O) 6 . Different configurations were observed in 3-methylcatechol-(H 2 O) 4,5 . Overall, the versatility of water and the different configurations of its clusters with fenchone can provide insight into the dynamic configurations of water in the liquid phase and help model their behavior.…”

“…Several spectroscopic techniques across the electromagnetic spectrum have been applied to these investigations including microwave rotational, terahertz vibration–rotation, infrared ion dip, and ultraviolet hole burning, among others. − Because of its high sensitivity to the spatial mass distribution, rotational spectroscopy has the unique advantage of being able to distinguish between close configurations (conformers and isomers), which makes it an extremely powerful technique for structural analysis. − The development of chirped pulse Fourier transform microwave (CP-FTMW) spectroscopy, with the capacity of recording large sections of the spectrum at once, has further advanced the study of microsolvated complexes, revealing a wealth of species produced in supersonic jets. Recent reports include complexes with a large number of isomers, such as limonene-(H 2 O) 1,2 , , aggregates of various sizes between difluoromethane and water, and complexes with a large number of water molecules, such as β-propiolactone-(H 2 O) 1–5 , 3-methylcatechol-(H 2 O) 1–5 , 3-methyl-3-oxetanemethanol-(H 2 O) 1–6 , glycolaldehyde-(H 2 O) 1–6 , benzaldehyde-(H 2 O) 1–6 , and ethanolamine-(H 2 O) 1–7 . Usually more than one isomer is observed for complexes with up to three waters.…”

Unveiling the Role of Water on π–π Stacking Through Microwave Spectroscopy of (Thiophene)2-(Water)1–2 Clusters

“…Isolated water molecules exist in two nuclear spin isomers, known as “ para” and “ ortho” , which are determined by the overall spin of their two hydrogen nuclei. The exchange of the two equivalent protons (Fermions) is often feasible if the water hydrogens are not involved in hydrogen bonding or only engaged in weak hydrogen bonds. , It is easy to understand that hydrogen bonding can hinder the large-amplitude motion that is associated with the exchange. In this study, we have observed the spectra of both ortho -H 2 O and para -H 2 O in the context of (C 4 H 4 S) 2 -H 2 O_I, where water is situated between two thiophene rings and participates in two O–H···π bonds.…”

“…Experimentally characterizing the structures of molecular clusters formed in a stepwise manner can provide valuable insights into the initial stages of solvation. Chirped pulse Fourier transform microwave (CP-FTMW) spectroscopy has proven to be an effective method for precisely characterizing gas-phase clusters in recent years. − In this study, we employ CP-FTMW spectroscopy to investigate the thiophene-water clusters generated through supersonic expansion. The stepwise microsolvated clusters involving thiophene monomers and dimers were identified by the analysis of their rotational spectra.…”

Binary conformers of a flexible, long-chain fluoroalcohol: dispersion controlled selectivity and relative abundances in a jet

“…To strive for an as complete as possible conformational search, we utilized CREST (Conformer-Rotamer Ensemble Sampling Tool), a powerful searching approach which combines semiempirical GFN-xTB 20 quantum chemistry methods with a metadynamics driven search algorithm, 21,22 in addition to manual potential energy surface (PES) scans along several important dihedral angles. The CREST approach has been successfully utilized by rotational spectroscopists for exploring conformational landscapes of a wide range of (in)organic compounds, 23,24 hydrogen-bonded clusters 25,26 and even very weakly bound van der Waals clusters. 27 About 1500 CREST binary TFB candidates were generated and a multi-tier approach 28 was used to identify low energy candidates.…”