Hydrogen bonding networks and cooperativity effects in the aqueous solvation of trimethylene oxide and sulfide rings by microwave spectroscopy and computational chemistry

Abstract

The intermolecular interactions responsible for the microsolvation of the highly flexible trimethylene oxide (TMO) and trimethylene sulfide (TMS) rings with one and two water (w) molecules were investigated using rotational spectroscopy (8-22 GHz) and quantum chemical calculations. The observed patterns of transitions are consistent with the most stable geometries of the TMO-w, TMO-(w)2 and TMS-w complexes at the B2PLYP-D3(BJ)/aug-cc-pVTZ level and were confirmed using spectra of the 18 O isotopologue. Due to its effectively planar backbone, TMO offers one unique binding site for solvation while water can bind to the puckered TMS ring in either an axial or equatorial site of the heteroatom. In all clusters, the first water molecule binds in the σv symmetry plane of the ring monomer and serves as a hydrogen bond donor to the heteroatom. The second water molecule is predicted to form a cooperative hydrogen bonding network between the three moieties. Secondary C-H … O interactions are a key stabilizing influence in the trimers and also drive the preferred binding site in the TMS clusters with the axial binding site preferred in TMS-w and the equatorial form calculated to be more stable in the dihydrate. Using an energy partition scheme from symmetry-adapted perturbation theory for the O, S and Se containing mono-and dihydrates, the intermolecular interactions are revealed to be mainly electrostatic but the dispersive character of the contacts is enhanced with increasing size of the ring's heteroatom due to the key role of longer-range secondary interactions.

Microhydrated 3‐Methyl‐3‐oxetanemethanol: Evolution of the Hydrogen‐Bonding Network from Chains to Cubes

“… [55] The geometry remains planar in the microsolvation environment involving one or two water molecules. [4] With the introduction of the substituents to the oxetane moiety, the ring is often distorted due to the increased eclipsing interactions. The puckering angle of the oxetane unit in MOM‐I a is 11.0°, which is typical for a 3,3‐disubstituted oxetane (about 10°), [54] whereas that in MOM‐II a is 21.9°.…”

Microwave Spectrum of Two‐Top Molecule: 2‐Acetyl‐3‐Methylthiophene

“…Each vibrational level is three-fold degenerated, and therefore, no torsional splitting is observed in the spectrum. [4] The molecule can be considered as a rigid rotor, with thousands of examples previously studied using high resolution rotational spectroscopy, stretching several important subjects from fundamental interest, [5][6][7] structure determination, [8][9][10] astrophysics, [11][12][13] biomolecules, [14][15][16] chirality [17][18][19] to microsolvation [20][21][22] and complexes. [23,24] A barrier of zero, on the other hand, describes a free internal rotor where all energy levels except the first one are two-fold degenerated, as shown, e. g., for the methyl group in CH 3 À C�CÀ CF 3 .…”

Microhydrated 3‐Methyl‐3‐oxetanemethanol: Evolution of the Hydrogen‐Bonding Network from Chains to Cubes

“…[55] The geometry remains planar in the microsolvation environment involving one or two water molecules. [4] With the introduction of the substituents to the oxetane moiety, the ring is often distorted due to the increased eclipsing interactions. The puckering angle of the oxetane unit in MOM-I a is 11.0°, which is typical for a 3,3disubstituted oxetane (about 10°), [54] whereas that in MOM-II a is 21.9°.…”

“…In this regard, the properties of the oxetane-containing compounds in different chemical environments, including the flexibility of the four-membered ring, the reactivity of the ether moiety, and the cooperativity of the hydrogen bond (H-bond), are of particular concern. [4,5] Rotational spectroscopy, which can characterize molecules in the gas phase with high structural sensitivity, [6] offers a robust approach to study these molecules in the "interaction-free" environment of the gas phase. During solvation processes, their physical and chemical properties, such as conformational preferences, may deviate from those in vacuum or in the solution phase.…”