Application of Proton Magnetic Resonance to Rotational Isomerism in Halotoluenes. VII. Barriers to Rotation and Conformational Preferences in α,α,α′,α′,2,4,5,6-Octachloro-m-xylene

At low temperatures α,α,α′,α′,2,4,5,6-octachloro-m-xylene exists as three conformers in solution and the proton resonance spectrum can be assigned by comparison to the spectrum of α,α,α′,α′,2,4,6-heptachloro-m-xylene. The temperature dependent spectra of the former in toluene-d8 solution are fitted to computed spectra based on a set of coupled Bloch equations. The activation parameters for the rotation about the sp2–sp3 carbon–carbon bonds are Ea = 14.93 ± 0.13 kcal/mol, log A = 12.45 ± 0.09, ΔH≠ = 14.30 ± 0.14 kcal/mol, ΔS≠ = −2.0 ± 0.5 e.u., ΔG≠ = 14.9 ± 0.05 kcal/mol at 298 °K. The quoted errors are standard deviations.