Tuning Intermolecular Interactions for Chiral Analysis: The Microwave Spectra and Molecular Structures of the Chiral Tag Candidates - and -2-Fluoro-3-(trifluoromethyl)oxirane and Their Gas-Phase Heterodimers with the Argon Atom.

The and isomers of the chiral tagging candidate molecule, 2-fluoro-3-(trifluoromethyl)oxirane, as well as the lowest energy gas-phase heterodimer of each with the argon atom, are characterized via quantum chemistry calculations and microwave rotational spectroscopy from 5 to 18 GHz and their ground state, vibrationally averaged structures, are determined. Apart from the / nature of the ring substitution and small differences in the dihedral angle specifying the rotation of the trifluoromethyl group, the two oxirane molecules and their respective argon complexes each have remarkable structural similarity. In contrast, the binding mode of argon to the oxirane, while similar for the two complexes here, is distinct from those modes observed in previous argon-fluorooxirane species.

Modulating Electrostatic Properties and Noncovalent Interactions via Structural Isomerism: The Microwave Spectra and Molecular Structures of ()- and ()-1,2,3,3,3-Pentafluoropropene and Their Gas-Phase Heterodimers with the Argon Atom.

Microwave spectra of both the and isomers of 1,2,3,3,3-pentafluoropropene along with all three of the singly substituted C isotopologues for each are obtained using broadband chirped-pulse Fourier transform microwave spectroscopy from 2.0-18.1 GHz.

Preserving the symmetry of cis-1,2-difluoroethylene in the gas-phase heterodimer with hydrogen chloride: A microwave rotational study revealing a novel structure.

The microwave spectra of three isotopologues of the gas-phase heterodimer formed between cis-1,2-difluoroethylene and hydrogen chloride are obtained in the 5-21 GHz region using Fourier transform microwave spectroscopy. The molecular structure, determined from the analysis of the spectra and supported by quantum chemistry calculations, has the hydrogen atom of the hydrogen chloride molecule interacting with both fluorine atoms of the fluoroethylene and no interaction between the chlorine atom and the olefin. Although the equilibrium structure has two inequivalent H⋯F interactions, zero-point motion averages over the two equivalent choices for these interactions, rendering the pairs of like atoms (C, H, and F) of the fluoroethylene equivalent, retaining the C2v symmetry of the olefin.

Microwave Spectrum and Novel Molecular Structure of ()-1-Chloro-3,3,3-trifluoropropene-Acetylene.

The gas-phase heterodimer formed between ()-1-chloro-3,3,3-trifluoropropene and acetylene is investigated using quantum chemistry calculations and observed via chirped-pulse Fourier transform microwave (FTMW) spectroscopy. Subsequent analysis of higher resolution spectra, including those using a sample enriched in HCCH, obtained with a Balle-Flygare FTMW spectrometer reveals a novel structure, as predicted by theory, for the complex, in which the acetylene functions as the gas-phase (Lewis) base and the halopropene as the acid. In the equilibrium structure, the acetylene molecule is located perpendicular to the symmetry plane of ()-1-chloro-3,3,3-trifluoropropene with the triple bond interacting with the two olefinic hydrogens.

Molecular Structures and Microwave Spectra of the Gas-Phase Homodimers of 3-Fluoro-1,2-epoxypropane and 3,3-Difluoro-1,2-epoxypropane.

Molecular structures for the heterochiral and homochiral gas-phase homodimers of 3-fluoro-1,2-epoxypropane and 3,3-difluoro-1,2-epoxypropane are investigated using both ab initio and density functional quantum chemistry calculations. Although microwave spectra for the heterochiral dimers are not observed as the lowest-energy isomers lack an electric dipole moment and others are presumably too high in energy, rotational spectra are observed for the homochiral dimers of each molecule that are consistent with the lowest-energy isomers of each. The presence of hydrogen atoms in the fluoromethyl groups makes it possible for these groups to participate in the intermolecular interactions that stabilize these dimers, resulting in a distinctly different bonding motif than is observed in the homodimers of 3,3,3-trifluoro-1,2-epoxypropane where the lack of a hydrogen atom prevents this possibility.

Examining the gas-phase homodimers of 3,3,3-trifluoro-1,2-epoxypropane using quantum chemistry and microwave spectroscopy.

Gas phase homodimers of 3,3,3-trifluoro-1,2-epoxypropane (TFO), a molecule which has shown promise as an effective chiral tag for determining the absolute stereochemistry and the enantiomeric composition of chiral analytes, are explored using a variety of quantum chemistry models and rotational spectroscopy. The potential surface governing the interaction of the two molecules is rapidly explored using the artificial bee colony algorithm for homodimer candidates that are subsequently optimized by quantum chemistry methods. Although all model chemistries employed agree that the lowest energy form of the heterochiral homodimer of TFO ( or ) is lower in energy than that of the homochiral dimer ( or ), the energy spacings among the lower energy isomers of each and indeed the absolute energy ordering of the isomers of each are very model dependent.

Straining to Put the Pieces Together: The Molecular Structure of ()-1-Chloro-1,2-difluoroethylene-Acetylene from Microwave Spectroscopy.

The microwave, rotational spectrum between 5.6 and 19.7 GHz of the gas-phase heterodimer formed between acetylene and ()-1-chloro-1,2-difluoroethylene is obtained using both broadband, chirped-pulse and narrow band, Balle-Flygare Fourier transform microwave spectrometers.

Assessing the performance of rotational spectroscopy in chiral analysis.

The capabilities of rotational spectroscopy-based methods as tools to deliver accurate and precise chirality-sensitive information are still breaking ground, but their applicability in the challenging field of analytical chemistry is already clear. In this mini review, we explore the current abilities and challenges of two emergent techniques for chiral analysis based on rotational spectroscopy. For that, we will showcase the two methods (microwave 3-wave mixing and chiral tag rotational spectroscopy) while testing their performance to solve the absolute configuration and the enantiomeric excess of a blind sample containing a mixture of enantiomers of styrene oxide.

Microwave Spectrum and Molecular Structure of 3-Fluoro-1,2-epoxypropane and the Unexpected Structure of Its Complex with the Argon Atom.

In common with the homologous 3,3-difluoro- and 3,3,3-trifluoro-species, 3-fluoro-1,2-epoxypropane is a small chiral molecule with a simple rotational spectrum, making it potentially useful for chiral analysis via conversion of enantiomers into spectroscopically distinct diastereomers through formation of noncovalently bound complexes. The rotational spectrum of 3-fluoro-1,2-epoxypropane (FO) and of its heterodimer with the argon atom are obtained, along with several isotopologues of each, using Fourier transform microwave spectroscopy from 5.6 to 18.

The Importance of How the Pieces Fit Together: The Microwave Spectrum and Molecular Structure of 2-Chloro-1,1-Difluoroethylene-Acetylene.

Fourier transform microwave spectroscopy is used to obtain the rotational spectrum of the gas-phase heterodimer formed between 2-chloro-1,1-difluoroethylene and acetylene between 5.1 and 20.0 GHz.

Exploring the sterically disfavored binding of acetylene to a geminal olefinic hydrogen-fluorine atom pair: The microwave spectrum and molecular structure of cis-1,2-difluoroethylene-acetylene.

The microwave rotational spectrum of the gas-phase bimolecular heterodimer formed between cis-1,2-difluoroethylene and acetylene is obtained using Fourier transform microwave spectroscopy from 5.9 to 21.2 GHz.

Exploring the Forces Contributing to Noncovalent Bonding by Microwave Spectroscopy and Structural Characterization of Gas-Phase Heterodimers of Protic Acids with Haloethylenes.

A detailed comparison of structural parameters obtained via microwave rotational spectroscopy in a systematic study of protic acid-haloethylene heterodimers is used to investigate the forces contributing to intermolecular interactions. Conclusions reached using structural data and chemical intuition are supplemented with information obtained from quantum-chemistry calculations to refine the understanding of the various contributions to complex formation. The observed structures, representative of the global minimum on the potential energy surface, are found to reflect a balance between optimal electrostatics and steric requirements, or in other words, how well the two interacting molecules fit together.

Finding the Better Fit: The Microwave Spectrum and Sterically Preferred Structure of trans-1,2-Difluoroethylene-Hydrogen Chloride.

The rotational spectrum of the gas-phase bimolecular heterodimer formed between trans-1,2-difluoroethylene and hydrogen chloride is obtained using Fourier transform microwave spectroscopy from 5.6 to 20.6 GHz.

Microwave Spectrum and Molecular Structure of the Chiral Tagging Candidate, 3,3,3-Trifluoro-1,2-epoxypropane and Its Complex with the Argon Atom.

The rotational spectrum of the chiral tagging candidate molecule, 3,3,3-trifluoro-1,2-epoxypropane (TFO), and of its heterodimer with the argon atom, is obtained using Fourier transform microwave spectroscopy from 5.6 to 18.1 GHz.

The Microwave Spectrum and Molecular Structure of (Z)-1-Chloro-2-Fluoroethylene-Acetylene: Demonstrating the Importance of the Balance Between Steric and Electrostatic Interactions in Heterodimer Formation.

The structure of the gas-phase heterodimer formed between (Z)-1-chloro-2-fluoroethylene and acetylene is determined via Fourier transform microwave spectroscopy from 5.5 to 20.8 GHz.

The gas-phase structure of the asymmetric, trans-dinitrogen tetroxide (NO), formed by dimerization of nitrogen dioxide (NO), from rotational spectroscopy and ab initio quantum chemistry.

We report the first experimental gas-phase observation of an asymmetric, trans-NO formed by the dimerization of NO. In additional to the dominant NO species, rotational transitions have been observed for all species with single N and O substitutions as well as several multiply substituted isotopologues. These transitions were used to determine a complete substitution structure as well as an r structure from the fitted zero-point averaged rotational constants.

Effect of Chlorine Substitution in Modulating the Relative Importance of Two Intermolecular Interactions: The Microwave Spectrum and Molecular Structure of (E)-1-Chloro-2-fluoroethylene-HCl.

Fourier transform microwave rotational spectroscopy is used to determine the structure of the gas-phase bimolecular complex formed between (E)-1-chloro-2-fluoroethylene and hydrogen chloride. Extensively split by nuclear quadrupole hyperfine structure and isotopic dilution, the spectrum is first identified via weak features observed using a broadband chirped pulse spectrometer in the 5.6-18.

Infrared rovibrational spectroscopy of OH-C2H2 in (4)He nanodroplets: Parity splitting due to partially quenched electronic angular momentum.

The T-shaped OH-C2H2 complex is formed in helium droplets via the sequential pick-up and solvation of the monomer fragments. Rovibrational spectra of the a-type OH stretch and b-type antisymmetric CH stretch vibrations contain resolved parity splitting that reveals the extent to which electronic angular momentum of the OH moiety is quenched upon complex formation. The energy difference between the spin-orbit coupled (2)B1 (A″) and (2)B2 (A') electronic states is determined spectroscopically to be 216 cm(-1) in helium droplets, which is 13 cm(-1) larger than in the gas phase [Marshall et al.

Effect of acid identity on the geometry of intermolecular complexes: the microwave spectrum and molecular structure of vinyl chloride-HF.

The structure of the gas-phase bimolecular complex formed between vinyl chloride and hydrogen fluoride is determined using Fourier transform microwave spectroscopy from 6.3 to 21.4 GHz.

A longitudinal assessment of periodontal disease in 52 Miniature Schnauzers.

Background: Periodontal disease (PD) is the most widespread oral disease in dogs and has been associated with serious systemic diseases. The disease is more prevalent in small breeds compared to large breeds and incidence increases with advancing age. In prevalence studies 84% of Beagles over the age of 3 and 100% of Poodles over the age of 4 were diagnosed with PD.

The molecular structure of and interconversion tunneling in the argon-cis-1,2-difluoroethylene complex.

Guided by ab initio predictions, the structure of the gas-phase complex formed between cis-1,2-difluoroethylene and an argon atom in a pulsed molecular jet is determined using microwave spectroscopy in the 5.7-21.5 GHz region of the spectrum.

Microwave spectrum and molecular structure of vinyl chloride-acetylene, a side binding complex.

The structure of the gas-phase bimolecular complex formed between vinyl chloride and acetylene is determined using a combination of broad-band, chirped-pulse, and narrow-band, Balle-Flygare Fourier transform microwave spectroscopy from 5.8 to 20.7 GHz.

Rotational spectroscopy and molecular structure of the 1-chloro-1-fluoroethylene-acetylene complex.

Guided by ab initio calculations, Fourier transform microwave spectra in the 6-21 GHz region are obtained for seven isotopomers of the complex formed between 1-chloro-1-fluoroethylene and acetylene. These include the four possible combinations of (35)Cl- and (37)Cl-containing CH(2)CClF with the most abundant acetylene isotopic modification, HCCH, and its H(13)C(13)CH analogue, as well as three singly substituted deuterated isotopomers. Analysis of the spectra determines the rotational constants and additionally, the complete chlorine quadrupole hyperfine coupling tensors in both the inertial and principal electric field gradient axis systems, and where appropriate, the diagonal components of the deuterium quadrupole coupling tensors.

Rotational spectroscopy and molecular structure of the 1,1,2-trifluoroethylene-hydrogen chloride complex.

Fourier transform microwave spectra in the 6-20 GHz region are obtained for the complex formed between 1,1,2-trifluoroethylene and hydrogen chloride, including both (35)Cl and (37)Cl isotopomers. Analysis of the spectra provides rotational constants and additionally, the complete quadrupole hyperfine coupling tensor in both the inertial and principal electric field gradient axis systems. The inertial information contained in the rotational constants combined with the results of the hyperfine analysis provides the structure for CF(2)CHF-HCl.