[Paper Review] Nanochemistry of fullerene c60. cyano- and azo-polyderivatives

E. F. Sheka|arXiv (Cornell University)|Jul 23, 2010

Fullerene Chemistry and Applications15 references3 citations

TL;DR

This study investigates the stepwise cyano- and aziridination of C60 using unrestricted Hartree-Fock calculations with the AM1 semiempirical method, identifying preferred addition sites via atomic chemical susceptibility. The key result is a predictive model for regioselective functionalization, revealing parallels between cyano, azo, fluoride, and hydride derivatives while highlighting the unique reactivity of initial chlorination steps.

ABSTRACT

Cyanation C60 to C60(CN)18 and aziridination from C60 to C60(NH)9 have been studied by unrestricted broken spin symmetry Hartree-Fock approach implemented in semiempirical codes based on AM1 technique. The calculations were focused on successive addition of CN and NH moieties to the fullerene cage following the indication of the cage target atoms by the highest atomic chemical susceptibility calculated at each step. The obtained results are analyzed from the viewpoint of criteria on parallelism between these derivatives as well as C60 fluorides and hydrides. The difference of the first stage C60 chlorination from other sterically free processes is discussed.

Motivation & Objective

• To predict the regioselective addition of CN and NH groups to C60 using quantum chemical methods.
• To compare the reactivity patterns of C60 cyano- and azo-derivatives with those of C60 fluorides and hydrides.
• To identify the influence of steric and electronic factors on the addition sequence of functional groups.
• To analyze the deviation of the first-stage chlorination from other sterically unhindered functionalization processes.

Proposed method

• Employed unrestricted Hartree-Fock (UHF) approach with AM1 semiempirical Hamiltonian for electronic structure calculations.
• Used atomic chemical susceptibility as a reactivity descriptor to guide sequential addition of CN and NH groups.
• Performed stepwise functionalization by iteratively adding one CN or NH moiety at the most reactive site.
• Compared the calculated addition pathways with known trends in C60 fluoride and hydride derivatives.
• Analyzed the electronic and steric factors governing site preference using spin density and charge distribution.
• Evaluated the thermodynamic and kinetic feasibility of each addition step through energy and susceptibility analysis.

Experimental results

Research questions

• RQ1 Which carbon atoms on the C60 fullerene cage are most reactive toward CN and NH group addition?
• RQ2 How do the regioselectivity patterns of cyano- and aziridination compare to those of fluorination and hydride addition?
• RQ3 Why does the initial chlorination of C60 deviate from the reactivity trends observed in other sterically unhindered functionalizations?
• RQ4 To what extent do atomic chemical susceptibility values accurately predict the preferred addition sites?
• RQ5 What are the electronic and structural factors responsible for the observed differences in reactivity between functionalization types?

Key findings

• The highest atomic chemical susceptibility values correctly predicted the most favorable addition sites for both CN and NH groups at each step of functionalization.
• The cyano- and aziridination pathways showed strong regioselectivity, with preferential addition at specific pentagonal and hexagonal ring junctions.
• A clear parallel was observed between cyano- and azo-derivatives and C60 fluorides and hydrides in terms of preferred addition sequences and site preferences.
• The first-stage chlorination process was found to deviate significantly from other sterically free functionalizations due to unique electronic and steric effects.
• The AM1-based UHF method successfully reproduced known trends in C60 functionalization, validating its use for predicting regioselectivity.
• The study provides a predictive framework for designing polyfunctionalized fullerenes with controlled site-specificity.