Determination of the rotational isomerization rate along carbon–carbon single bonds in solution

Abstract

The temperature- and viscosity-dependent rotational isomerization time constant (τ_rot) along the C–C˙ bond of CF₂BrCF₂ radical in solution was measured using femtosecond infrared spectroscopy after photodissociating the I atom from CF₂BrCF₂I. Three density functional theory (DFT) functionals, ωB97XD, APFD, and B3LYP were used with the aug-cc-pVTZ basis set to calculate the required parameters in calculating τ_rot using Kramers’ theory of reaction rates. The measured τ_rot was consistent with the value calculated using the vibrational frequencies and rotational barriers of the related compounds calculated by DFT method with ωB97XD/aug-cc-pVTZ. Kramers’ theory calculation of τ_rot was further verified by an experimental measurement for CF₃CF₂CF₂˙ in CCl₄ at 293 K. The τ_rot along the C–C(˙) bond of ethyl radical and ethane derivatives in solution can be reliably estimated by Kramers’ theory combined with DFT calculations using the ωB97XD functional and aug-cc-pVTZ basis set.