Axial and equatorial hydrogen-bond conformers between (CH2)3S and H(D)F: Fourier transform infrared spectroscopy and ab initio calculations

Abstract

The coexistence of axial and equatorial hydrogen-bonded conformers of 1 : 1 (CH(2))(3)S-HF (and -DF) has been observed in the same adiabatic expansion of a supersonic jet seeded with argon and in a static absorption cell at room temperature. High level calculations computed the axial conformer to be the most stable one with a small energy difference with respect to the equatorial one, in full agreement with previous microwave experiments. On the grounds of band contour simulations of FTIR spectra and ab initio energetic and anharmonic vibrational calculations, two pairs of ν(s) HF donor stretching bands, observed in a series of jet-FTIR spectra at 3457.9 and 3480.5 cm(-1) have been respectively assigned to the axial and equatorial forms of the 1 : 1 complex. In the jet-FTIR spectra series with HF, the assignment of an additional broad band (about 200 cm(-1) higher in frequency with respect to ν(s)) to a 1 : 2 complex has been supported by theoretical investigations. Experimental detection of both axial and equatorial forms of a cyclic trimer has been confirmed by calculated energetic and vibrational properties. The nature of hydrogen bonding has been examined within topological frameworks. The energetic partitioning within the 1 : 1 dimers has been elucidated with SAPT techniques. Interestingly, the interconversion pathway between two 1 : 1 structures has been explored and it was seen that the formation of the 1 : 1 complex affects the interconversion barrier on the ring puckering motion. The band contour analysis of gas phase FTIR experiments provided a consistent set of vibrational frequencies and anharmonic coupling constants, in good agreement with ab initio anharmonic vibrational calculations. Finally, from a series of cell-FTIR spectra recorded at different partial pressures of (CH(2))(3)S and HF monomers, the absorption signal of the 1 : 1 complex could be isolated which enabled to estimate the equilibrium constant K(p) = 0.023 at 298 K for the dimerization.

Similar Strength of the NH···O and NH···S Hydrogen Bonds in Binary Complexes

“…Furthermore, the equilibrium constant upon complexation is determined by combining calculated and measured intensities. This method has proven to provide good estimates for thermodynamic equilibrium constants in other studies. ,,,, …”

“…Fourier transform infrared (FTIR) spectroscopy has proven to be important in the detection of hydrogen-bonded complexes. − Both the expected redshift (ii) and intensity enhancement (iii) of the X–H stretching frequency upon complexation can be detected, and the experimental results can be directly compared to ab initio quantum mechanical calculations. An advantage of gas-phase FTIR spectroscopy, in contrast to, for example, matrix isolation, is that the system is in equilibrium, which makes it possible to obtain information about the equilibrium constant.…”

“…This method has proven to provide good estimates for thermodynamic equilibrium constants in other studies. 9,10,17,18,33 ■ EXPERIMENTAL SECTION DMS (Aldrich, ≥99%) was purified with two freeze−pump− thaw cycles before every usage. DMA (Aldrich, anhydrous, 99+ %) and DME (Aldrich, anhydrous, ≥99%) were used without further purification.…”

Nonbonding pairs in cyclic thioethers: Electrostatic modeling and ab initio calculations for complexes of 2,5‐dihydrothiophene, thietane, and thiirane with hydrogen fluoride

“…The energy order of the minima in the V ( ϕ ) vs ϕ plot for thietane has the equatorial minimum lower in energy than that of the axial minimum and the ϕ min values are somewhat smaller in magnitude than those from experiment. The microwave result is confirmed by a high‐resolution, infrared spectroscopy investigation of thietane⋯HF …”

“…The microwave result is confirmed by a high-resolution, infrared spectroscopy investigation of thietaneÁ Á ÁHF. [68] FIGURE 3 Models of the geometries of the three cyclic thioethers thiirane, thietane, and 2,5-dihydrothiophene (to scale). The geometries are those that result from calculations at the CCSD(T)-F12c/cc-pVTZ-F12 level of theory…”