25 Jun 2013

Trends in Measured Redox Potentials and Computed Molecular Orbital Energies of Derivatized Buckminsterfullerenes

Lab Experiment

Submitted by Robert Q. Topper, Cooper Union
Categories
Description: 

In this project students are asked to reproduce published calculations of molecular orbital energies of a series of derivatized fullerenes and correlate them with published reduction and oxidation potentials obtained from cyclic voltammetry. The particular subset of the derivatives to be studied are chosen by the student and this choice is part of the learning activity. The students then carry out additional calculations using other theoretical models to see whether they improve the correlation between computed and experimental properties. Interpretation of the trends and suggestions for additional work are discussed in a formal report. 

Learning Goals: 

After completing this project, students will be able to

  • Summarize the use of cyclic voltammetry to measure redox potentials;
  • Use computer software to build and visualize molecular models of derivatives of buckminsterfullerene;
  • Carry out density functional theory and semiempirical calculations of buckminsterfullerenes;
  • Discuss how derivatization affects the energies of the frontier orbitals;
  • Implement different theoretical models and correctly choose the one which best correlates with the experimental data;
  • Discuss which computational method is likely to be most useful in the prediction of redox potentials from first principles; and
  • Write a formal report describing their findings.
Equipment needs: 

Modern computer workstation with 6+ GB RAM; molecular structure building and visualization software; quantum mechanics software. Spartan 8 has all of the capabilities required for this project.

 

Implementation Notes: 

The models are built and the calculations are carried out at our institution using Spartan 10, but Gaussian, GAMESS, Q-Chem, NW-Chem or other programs with similar capabilities could be used instead. 

Time Required: 
Students are asked to complete this as an independent project, although the work could be done as a group in one or two laboratory periods if a computer classroom is available.
Evaluation
Evaluation Methods: 

Students write a formal report which is evaluated with respect to whether each learning goal is achieved.

Evaluation Results: 

Earlier versions of this project have been assigned to approximately 30 students in three senior-level inorganic chemistry courses over a six year period, with substantial revisions made each time. Students were generally able to reproduce the literature results successfully and to gauge which method is expected to be most reliable for first-principles calculations of redox potentials. There was some variability in students’ choice of fullerenes which appropriately span the range of interest. Some students were able to make fairly sophisticated suggestions for future work. 

Creative Commons License: 
Creative Commons Licence

Comments

This is a great introduction to electrochemistry. I actually started using this in my physical chemistry course.

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