Figure 3.

Delocalization dominates trends in “strain release” ring-opening reactions. (a) Test set of acyclic, monocyclic, and fused polycyclic hydrocarbons. (b) BEP plot (predicted vs calculated ΔH^‡, kcal mol^–1) for the addition of methyl radical to the red bonds of the molecules in the test set. The blue dashed line denotes perfect correlation. (c) Prediction of ΔH^‡ from ΔH_r and χ_NBO (eq 3). (d) Breakdown of strain and delocalization (χ_NBO) contributions to ΔΔH^‡ (kcal mol^–1) for the addition of methyl radical to the test set, relative to bicyclo[2.2.0]hexane (G), with α = 0.51 and β = −192.4 kcal mol^–1 e^–1. Asterisks indicate the cases where delocalization dominates over strain release.