DFT Study for Substitution Patterns of C20H18X2Regioisomers (X = F, Cl, Br, or OH)

We used the hybrid density-functional (B3LYP/6-31G(d,p)) method to analyze the substitution patterns of C20H18X2 derivatives (X = F, Cl, Br, or OH) obtained as disubstituted C20H20 cages. Our results suggest that the cis-1 regioisomers (1,2-dihalo derivatives) are less stable than the trans-1 regioisomers (1,20-dihalo derivatives), whereas in the case of the dihydroxy derivatives, the cis-1 regioisomer is more stable than the trans-1 regioisomer. This implies that in the dihalo-induced strain cages of C20H18X2, the strain effect would affect the relative energies, while in the dihydroxide, the hydrogen bonds have a stronger effect on the relative energies in cis-1 regioisomer than the strain effect do. Thus this supports the experimental result in which the bisvicinal tetrol was of particular preparative-synthetic interest as a substitute for the lacking bisvicinal tetrabromide. Further, the topologies of the HOMO and LUMO characteristics of all C20H18Cl2 and C20H18Br2 regioisomers with the same symmetry are same, but they are different from those of C20H18F2 and C20H18(OH)2. This indicates that the five regioisomers of each C20H20 disubstituted derivative will have an entirely different set of characteristic chemical reactions.