Fig. 2.

(A) Alkyl-bridged diene model compound with seven bridging σ bonds. The alkane bridge is planar, and the left and right C=C bonds are twisted approximately ${60}^{\text{o}}$ in opposite directions out of the CC-bonded bridge plane. These double bonds are taken to be the D and A. In our computations (Fig. 3), the number of bridge σ bonds is varied from 4 to 13. (B) Example of disordered alkyl-bridged diene model compound with seven bridging σ bonds used in the computations of Tables S1 and S2. (C) Norbornyl bridged diene model compound with two parallel C=C bonds (D and A). These compounds with n = 1, 2 are used in the computations shown in Tables S3 and S4. (D) Norbornyl bridged diene model compound with orthogonal C=C bonds (D and A) with symmetry-forbidden triplet EnT.