Fig. 4. (a) Plots of the cyclotrimerization energies against the substituents for the n-alkyl-substituted isocyanates. (b) Plots of the cyclotrimerization energies against the sum of the deformation energy of the isocyanurate ring and the intramolecular inter-substituent interaction energy in the isocyanate molecules. Red open triangle: C3 conformation of the n-alkyl-substituted isocyanurate, blue inverted triangles: Cs conformation of the n-alkyl-substituted isocyanurate, green opened diamond: secondary alkyl-substituted isocyanurates, black opened square: tri-t-butyl isocyanurate, and purple opened circle: triphenyl isocyanurate. The numerical values of the cyclotrimerization energies, the deformation energies of the isocyanurate rings, and the inter-substituent interaction energies are provided in Tables 6 (ONIOM (1)), 4, and 3, respectively.
