Diels–Alder [4+2] Cycloadditions of C20 with Some Diene and 1,2- Dioxo Compounds: A Theoretical Study

Diels–Alder [2+4] cycloaddition products of the reaction between C20 and C4H4X2 or C2O2X2 (X = H, F, Cl, CH3, NH2, NO2, and OH) were studied atB3LYP level of theory with 6-31G, 6-31G(d, p) and 6-311G(d, p) basis sets. The HOMO–LUMO gaps of Kohn–Sham orbitals for most of the adducts show evident increase compared with the gap value of C20, suggestive of more stability in the adducts. The thermodynamic calculations indicate that the reaction of diene with C20 is exothermic and spontaneous. While, the addition of 1,2-dioxos to C20 can be thermodynamically improper when the 1,2-dioxo group consists of electronegative atoms