Weak Hydrogen Bond Network: A Rotational Study of 1,1,1,2-Tetrafluoroethane Dimer

Weak hydrogen bonds between alkyl halides and amides: The microwave spectroscopic and theoretical study of the difluoromethane⋯formamide complex

The pure rotational spectrum of the complex of difluoromethane with formamide was investigated by means of microwave spectroscopy supplemented with theoretical calculations. The hyperfine structure arising from the ¹⁴N nuclear quadrupole coupling effect was completely resolved. The most stable isomer that displays the C_s symmetry with the ∠HCH angle of difluoromethane being bisected by the ab-plane of formamide was detected. The two moieties in the detected isomer are connected via one N-H⋯F and one bifurcated CH₂⋯O weak hydrogen bonds confirmed by the non-covalent interaction plot and natural bond orbital analyses. The distances of the NH⋯F and CH₂⋯O interactions were determined to be 2.140(14) Å and 2.749(14) Å, respectively. The NH⋯F bond angle was determined to be 150.7°. Symmetry-adapted perturbation theory analysis indicates that the electrostatic component is the largest contributor to the total attractive interaction energy of the difluoromethane⋯formamide complex.

Refractive Index at Low Temperature of Tetrachloromethane and Tetrafluoroethane Cryovacuum Condensates

We present low-temperature measurements of the refractive index of cryofilms of tetrachloromethane and 1,1,1,2-tetrafluoroethane at different condensation and measurement temperatures between 16 and 130 K. Using cryovacuum condensation, we have been able to obtain thin films in an amorphous state for both substances despite them being very bad glass formers. Then, we have studied the evolution of the refractive index with an increasing temperature, including by transitions to ordered or partially disordered crystalline states.

Shape and non-bonding interactions in the formic acid-difluoromethane complex by rotational spectroscopy

The rotational spectrum of the formic acid-difluoromethane complex was measured by using supersonic-jet Fourier transform microwave spectrometer. Experimental results and ab initio calculations support a conformation formed through a relative strong OH⋯F and a bifurcated weak CH₂⋯O hydrogen bonds. The distances of the non-bonding interactions were determined to be 1.960(2) Å and 2.797(3) Å for OH⋯F and CH₂⋯O, respectively. The dissociation energy of the complex is estimated to be about 1346 cm^-1. The bonding nature of the intermolecular interactions was revealed by non-covalent interaction analysis and electron density difference analysis.

Structure, Conformational Equilibria, and Weak Hydrogen Bonding in the CH2 F2 -CF3 CH2 F Dimer

To probe the multiple configurations of a weakly bound intermolecular complex, the difluoromethane and 1,1,1,2-tetrafluoroethane dimer was investigated by using pulsed jet Fourier transform microwave spectroscopy coupled with quantum chemical calculations. Three isomers were detected in the supersonic jet. Spectroscopic assignments, ab initio calculations and quantum theory of atoms in molecules (QTAIM) analyses prove that all the observed isomers are stabilized through a net of three weak C-H⋅⋅⋅F-C interactions. The interaction energies are estimated to be within 12-13 kJ mol^-1 , dominated by electrostatic and dispersion according to Symmetry-Adapted Perturbation Theory (SAPT) analysis. The spectroscopic measurements were also extended to three and two ¹³ C isotopologues in natural abundance for the isomers II and III, respectively, which lead to precisely structural determinations of these two isomers. The comparison of the relative intensity of these isomers measured in the carrier gases of argon and helium evidenced that isomer II is the global minimum, while the intensities measured in helium suggested that the population of the three isomers in the jet to be N_I /N_II /N_III ≈1/11/4.

Microwave spectroscopy of 2-(trifluoromethyl)pyridine⋯water complex: Molecular structure and hydrogen bond

In order to explore the -CF₃ substitution effect on the complexation of pyridine, we investigated the 2-(trifluoromethyl)pyridine⋯water complex by using pulsed jet Fourier transform microwave spectroscopy complemented with quantum chemical calculations. Experimental assignment and ab initio calculations confirmed that the observed complex is stabilized through N⋯H-O and O⋯H-C hydrogen bonds forming a five-membered ring structure. The bonding distance in N⋯H-O is determined to be 2.027(2) Å, whilst that in O⋯H-C interaction is 2.728(2) Å. The quantum theory of atoms in molecules analysis indicates that the interaction energy of N⋯H-O hydrogen bond is ∼22 kJ mol^-1 and that for O⋯H-C hydrogen bond is ∼5 kJ mol^-1. The water molecule lies almost in the plane of the aromatic ring in the complex. The -CF₃ substitution to pyridine quenches the tunneling splitting path of the internal motion of water molecule.