Rotation of the difluoromethyl group in 2,3,3-trifluoropropene results in three minima: a higher energy, achiral rotamer that contains a plane of symmetry and two equivalent, chiral lower-energy rotamers that form an enantiomeric pair. As revealed though the analysis of the microwave spectra of the gas-phase heterodimers formed between each rotamer and acetylene, the acetylene adopts a different bonding motif in each case. Furthermore, both modes of bonding are distinct from that observed in 1,2-difluoroethylene-acetylene where the acetylene interacts with an ethylenic fluorine-hydrogen pair located cis to each other, despite the existence of a similar pair in 2,3,3-trifluoropropene.

The interaction preferences of water with small molecules has been an area of interest for many years as we endeavor to better understand solvation at the molecular scale. Here, a study of the 1:1 weakly-bound complexes of γ-butyrolactone (GBL) with water is presented. GBL is a five-membered heterocycle that contains two distinct regions that could serve as binding sites for a single water. Matrix isolation FTIR experiments identified several peaks that were not associated with isolated water or GBL, implying the bands are due to weakly-bound complexes of the two. In addition to normal water, the spectra of and HDO complexes with GBL were also recorded. These spectra were interpreted with the aid of computational chemistry. In this work, multiple density functional theories and MP2 calculations were used to find minimum energy configurations and vibrational structure of the complexes. Possible interpretations of the experimental and computational results will be presented here.

Understanding the first interaction stages of water with organic molecules is of great interest given the ubiquity of water in nature. Here we explore the microsolvation of the eight-membered cyclic ketone cyclooctanone (CYO) using chirped pulse Fourier transform microwave spectroscopy. We previously assigned three conformers of CYO monomer and complexes of CYO···(H₂O)_1,2[1,2]. Cyclooctanone hydrates with higher number of water molecules, CYO···(H₂O)₃₋₇, have now been observed and identified with the aid of ab initio and DFT methods. Most of the complexes show several arrangements, highlighting the versatility of water molecules in their interactions with an organic solute. Binding preferences and relevant interactions will be discussed.

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E. Burevschi, I. Peña, M. E. Sanz, Phys. Chem. Chem. Phys. 2019, 21, 4331-4338.

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E. Burevschi, I. Peña, M. E. Sanz, J. Phys. Chem. Lett. 2021, 12, 12419-12425.

Carvone (C₁₀H₁₄O, 5-isopropenyl-2-methyl-2-cyclohexenone) is one of the most abundant monoterpenoids. It is present in many essential oils and released by plants to the atmosphere. Moreover, it is widely used as an odorant in household products, perfumes and cosmetics. Water is abundant in the atmosphere and in the mucus layer, and thus carvone interactions with water are of atmospheric and biological interest. We have studied the complexes of carvone with water using chirped pulse Fourier transform microwave spectroscopy in the 2-8 GHz frequency range. Supporting calculations have been carried out using MP2 and B3LYP-D3BJ methods. Eight different isomers of carvone-(H₂O) have been observed and identified based on the comparison between their experimental and theoretical rotational constants and the observation of the ¹⁸O water isotopologues. Water forms complexes with all observed conformations of carvone in the gas phase [1,2]. Binding preferences are dictated by the formation of O-H···O and C-H···O hydrogen bonds. To visualise these interactions and gain further insight on their relative strength, non-covalent interaction and natural bond orbital analyses were performed. We will discuss our results in the context of other complexes formed by carvone.

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J. R. A. Moreno, T. R. Huet and J. J. L. González, Struct. Chem., 2013, 24, 1163–1170.

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D. Loru, A. Vigorito, A. F. M. Santos, J. Tang and M. E. Sanz, PCCP, 2019, 21, 26111-26116.

Previously, the \emph{v}$_{1}$ and \emph{v}$_{5}$ bands of helium solvated nitric oxide clusters were investigated with a pulsed OPO system having a resolution of 0.25 cm$^{-1}$ [1]. Here, we investigated the \emph{v}$_{1}$ band with a continuous-wave quantum cascade laser at high resolution (10 MHz), and uncover substructure that provides additional insight. In particular, in the vicinity of the fundamental band of the nitric oxide dimer, we observed baseline-resolved rotational substructure with relative intensities that are consistent with the \emph{cis}-(ON-NO) isomer, along with a weaker band with similar substructure shifted slightly to lower frequencies. We tentatively attribute this weaker band to an anharmonic resonance between the fundamental and a combination band (which could be, e.g., 4\emph{v}$_{6}$ + \emph{v}$_{3}$), although we cannot rule out that it is due to the higher energy triplet nitric oxide dimer.\newline\newline [1] Hoshina et al., \emph{J Phys. Chem. A.} \textbf{2016}, 120, 527.

The MP2 and CCSD(T) methods have been used in conjunction with large correlation consistent basis sets to characterize simple dimers in which halogen-bonded configurations can be energetically competitive with the hydrogen-bonded structures [1,2]. In the case of dimers formed between HCN and a diatomic hydrogen halide molecule (HX where X = Cl, Br or I), the linear halogen-bonded arrangement (HCN…XH) is a local minimum with an electronic energy that gets closer to that of the corresponding linear hydrogen-bonded global minimum (HCN···HX) as the size of the halogen atom increases. These relative electronic energies decrease from around 4 kcal mol⁻¹ for X = Cl and roughly 3 kcal mol⁻¹ for X = Br to as little as 0.5 kcal mol⁻¹ for X = I near the CCSD(T) complete basis set (CBS) limit. The MP2 and CCSD(T) harmonic vibrational frequencies suggest that it may be feasible to differentiate between these structures spectroscopically. We have also conducted a similar analysis of the dimer formed between HI and acetonitrile (CH₃CN) to investigate the tentative assignment of a second feature in the HI stretching region of the infrared spectrum from matrix isolation experiments to the halogen-bonded configuration. In this system, both the hydrogen-bonded global minimum and the halogen-bonded local minimum have C_3v point group symmetry. The latter lies within 1 kcal mol⁻¹ of the former at the CCSD(T) CBS limit, and our harmonic vibrational frequencies corroborate the tentative assignment of that spectral feature in the HI stretching region to the halogen-bonded configuration (CH₃CN···IH). This work on small non-covalent dimers is being extended to azabenzene systems capable of interacting with multiple hydrogen halide molecules (e.g., C₄H₄N₂(HX)₂ and C₃H₃N₃(HX)₃).
[1] Perkins, M.A.; Tschumper, G.S.; Characterization of Competing Halogen- and Hydrogen-Bonding Motifs in Simple Mixed Dimers of HCN and HX (X = F, Cl, Br, and I), J. Phys. Chem. A, 2022, 126, 3688-3695. DOI: 10.1021/acs.jpca.2c02041 [2] Perkins, M.A.; Tschumper, G.S.; Characterization of Competing Halogen-Bonding and Hydrogen-Bonding Motifs in the Acetonitrile/Hydrogen Iodide Dimer, Chem. Phys., 2023, 568, 111843. DOI: 10.1016/j.chemphys.2023.111843

London Dispersion is an essential element of structural stability and thus affects chemical reactivity and selectivity. However, estimating London forces is challenging due to the omnipresent solvent or crystal lattice effects that attenuate attractive interactions. Here, we report a spectroscopic study of the intramolecular H-bond in five series of onium ions with a systematic increase in Dispersion energy donors (DEDs). Remarkably, the intramolecular H-bond might be localized/delocalized, and therefore its spectroscopic signature is used as a readout reflecting overall steric effects in the system. Therefore, we can probe a delicate London Dispersion - Pauli Repulsion balance by analyzing 2D PESs, applying different energy decomposition schemes, and performing a comparative analysis of experimental data obtained in the gas phase without any external encumbrances, including messenger tags. [1,2] Finally, considering these findings, we can tune the barrier’s height to achieve the desired reactivity for the intramolecular H-transfer reaction or, in other words, turn the hydrogen bond ON/OFF upon request. [1] V. Gorbachev, A. Tsybizova, L. Miloglyadova, P. Chen, J. Am. Chem. Soc. 2022, 144, 20, 9007–9022 [2] A. Tsybizova, E. Paenurk, V. Gorbachev, P. Chen, J. Phys. Chem. A 2020, 124, 41, 8519–8528