Thermodynamics of trans/gauche conformational equilibria and vibrational spectra of 1,2-dihaloethanes in various media

The recently developed efficient protocols to implicit [Grimme et al., J. Phys. Chem. A 125, 4039-4054 (2021)] and explicit quantum mechanical modeling of non-rigid molecules in solution [Katsyuba et al., J. Phys. Chem. B 124, 6664-6670 (2020)] are used to describe conformational equilibria of 1,2-dichloroethane and 1,2-dibromoethane in various media. Two approaches for evaluation of trans/gauche free energy differences, delta G(t-g), are compared: (a) direct delta G(t-g) computation in implicit solution; (b) the use, together with experimental intensities, of infrared absorption coefficients and Raman scattering cross sections computed for each explicitly modeled solution. The same cluster model of a solute surrounded by the first solvation shell of solvent molecules was used to simulate both Raman and IR spectra. The good agreement between the two approaches indicates the reliability of both methods. The importance of using correct absorption coefficients and Raman scattering factors for each medium is discussed. The delta G(t-g) estimates from both implicit and explicit solvation simulations were combined with experimentally measured enthalpy differences delta Ht-g available in the literature to obtain condensed-state delta St-g estimates.

Automated summary

The efficient protocols for modeling non-rigid molecules in solution have been used to study the conformational equilibria of 1,2-dichloroethane and 1,2-dibromoethane. The comparison between different approaches demonstrates their reliability, highlighting the importance of using accurate parameters for each medium.