The key feature of instability of small non-IPR closed-shell fullerenes: three isomers of C40

The molecular structures of non-IPR C40 fullerene isomers 31 (Cs), 38 (D2) and 39 (D5d) were studied using a semiempirical approach developed earlier for higher fullerenes. Quantumchemical calculations (DFT) showed that they have closed shells. The distributions of single, double and delocalized π bonds in the test isomer molecules and their molecular formulas are presented for the first time.