Fig. 4.

Ring inversion energetics of ^Th4 COT _Saddle and ^Th6 CDH _Screw. a, Conformational change of ^Th4 COT _Saddle calculated along the reaction coordinate. b, Conformational change of ^Th6 CDH _Screw calculated along the reaction coordinate. Gray-, green- and orange-colored drawings represent the conformations in the S₀, T₁, and S₁ states, respectively. For the S₀ and T₁ states, the structures were optimized at the B3LYP-D3(BJ)/6–31G(d) level, and the energy values were calculated by single-point calculations at the B3LYP-D3(BJ)/6–311+G(d,p) level using the optimized geometry. For the S₁ state, the structures were optimized at the TD-B3LYP-D3(BJ)/6–31+G(d,p) level, and the energy values were obtained by the same level of calculation used for the structural optimization. Activation enthalpies experimentally obtained (computationally calculated) are given in kcal mol^–1