Electronic vs Steric Effects on the Stability of Anionic Species: A Case Study on the Ortho and Para Regioisomers of Organofullerenes

The
stability of the anionic species of the ortho and para regioisomers
of (MeO)­BnC2n (Me = methyl, Bn = benzyl, n = 30 or 35) has been examined. The results show that the
ortho adducts (electronically favored regioisomers) are stable upon
receiving one or two electrons, while the para ones (sterically favored
adducts) decompose by removing the methoxy group under similar conditions.
Computational calculations indicate that the stability of the anionic
species is significantly affected by the electronic structure, where
the [5,6]-double bond is responsible for the instability of the reduced
species of the para adducts. Further study with 1,15-(MeO)2-2,4-Bn2C60, an adduct with both the ortho
and para positioned methoxy, shows that the reduced species is stable,
indicating that the 1,2,4,15-configuration is an electronically preferential
structure even though it has a [5,6]-double bond.