Reaction mechanisms

17 Jan 2020

Formal oxidation states in Ru-catalyzed water oxidation

Submitted by Margaret Scheuermann, Western Washington University
Evaluation Methods: 

I did not grade this activity.

Evaluation Results: 

Three students out of 14 explicitly mentioned that this activity was helpful on the free response section of the course evaluations.

Description: 

This LO is an in-class assignment to prepare students for literature readings involving catalytic cycles in which multiple protons and electrons are transferred. Students practice assigning oxidation states to complexes with aquo, oxo, superoxo, and hydroperoxo ligands then use this information to analyze a proposed water oxidation mechanism from the literature.

Students are asked to add in the substrates and products entering and leaving the catalytic cycle. While this is, at its heart, a stoichiometry excercise, it helps calibrate students for the level of attention to detail needed to effectively engage with reading about multi-electron catalytic mechanisms.

Learning Goals: 

After completing this activity:

A student should be able to assign formal oxidation states to monometallic complexes with aquo, oxo, hyrdoperoxo, and superoxo ligands

A student should be able to apply their knowledge of formal oxidation states to the analysis of a proposed mechanism of a catalytic water oxidation reaction

Corequisites: 
Subdiscipline: 
Prerequisites: 
Implementation Notes: 

I used this activity during a lab lecture before an inorganic laboratory experiment in which students would be preparing and testing the Ru-based OEC mimic. 

I began the class period with a brief review of L/X type ligands and formal oxidation states. 

Students then worked in groups to complete this activity. 

 

Other implementation options:

While I used this activity as part of a lab lecture it could also be used in a lecture setting or as part of a problem set.

It could also be modified for use as an equation balancing excercise in a majors or honors general chemistry course.

Time Required: 
10-20 minutes
2 Jan 2020

Reaction Mechanisms: Energy Profiles and Catalysts

Submitted by Wesley S. Farrell, United States Naval Academy
Evaluation Methods: 

Students will report answers to the class.  The instructor should use the quality of these responses to gauge understanding.

Evaluation Results: 

N/A

Description: 

This in class activity consists of two demonstrations to be performed by the instructor, followed by a worksheet that students may work on independently or in groups.  The demonstrations allow the students to determine when a reaction has occured, when it has not occured, and generate qualitative reaction energy profiles to match these observations.  This activity is designed to take place during a description of kinetics in general chemistry. Detailed descriptions of the procedure and activity may be found in the "Overview for Instructor."

Learning Goals: 

Students should be able to create qualitative reaction energy profiles which match a series of reactions, catalyzed and uncatalyzed.

Subdiscipline: 
Equipment needs: 
  • Three 8” test tubes
  • 3% H2O2
  • Small cubes of potato, both raw and cooked
  • 250 mL Erlenmeyer flask
  • Pt spiral (preferably in glass tube with hook for support)
  • Methanol
  • Bunsen burner (with striker)

 

Course Level: 
Corequisites: 
Prerequisites: 
Topics Covered: 
Implementation Notes: 

Please see the "Overview for Instructor" document for implementation notes.

Time Required: 
15 minutes
18 Oct 2019

Mechanisms of Mn-catalyzed water oxidation reactions

Submitted by Margaret Scheuermann, Western Washington University
Evaluation Methods: 

I did not grade this activity. 

Evaluation Results: 

Three students out of 14 explicitly mentioned that this activity was helpful on the free response section of the course evaluations.

 

Description: 

This LO is an in-class assignment to prepare students for literature readings involving catalytic cycles in which multiple protons and electrons are transferred. Two catalytic mechanisms, a proposed OEC mechanism and the proposed mechanism of a biomimetic OEC complexes are included. The intermediates are drawn including all charges and oxidation states, details which are sometimes omitted in the primary literature but can be helpful to students who are not accustomed to looking at multistep catalytic cycles. Students are then asked to add in the substrates and products entering and leaving the catalytic cycle. While this is, at its heart, a stoichiometry excercise, it helps calibrate students for the level of attention to detail needed to effectively engage with reading about bioinorganic catalytic mechanisms.

Learning Goals: 

After completing this activity:

A student will be able to follow along with each step in  proposed water oxidation mechanims in the literature.

A student will be able to apply their knowledge of stoichiomety to complex catalytic cycles involving electron transfer.

A student will be able to analyze and compare the details of catalytic cycles.

Corequisites: 
Subdiscipline: 
Prerequisites: 
Implementation Notes: 

I used this activity during a lab lecture before an inorganic laboratory experiment in which students would be preparing and testing an OEC mimic. The procedure we used was roughly based on a published procedure (J. Chem Ed. 2005, 82, 791) linked in web resources. 

I began the class period with a brief introduction to the chemistry of photosynthesis and where water oxidation and PSII fit in the broader picture. I then introduced the mimic that students would be preparing and the chemistry of the Oxone (R) triple salt. 

Students then worked in groups to complete this activity and discuss their structural and mechanistic observations. After the activity they were encouraged to read the papers referenced in the activity and to think about the evidence that supports the proposed mechanism.

 

Other implementation options:

While I used this activity as part of a lab lecture it could also be used to stimulate a discussion comparing structure/mechanism of biological and biomimetic systems in a lecture setting without the accompaning laboratory work.

This could also be modified for use as an equation balancing excercise in a majors or honors general chemistry course.

Time Required: 
10-20 minutes
8 Jun 2019

VIPEr Fellows 2019 Workshop Favorites

Submitted by Barbara Reisner, James Madison University

During our first fellows workshop, the first cohort of VIPEr fellows pulled together learning objects that they've used and liked or want to try the next time they teach their inorganic courses.

5 Jun 2019

Zinc-Zinc Bonds (Expanded and Updated)

Submitted by Wesley S. Farrell, United States Naval Academy
Evaluation Methods: 

Performance and participation in the discussion will be assessed 

Evaluation Results: 

None collected yet. Evaluation data will be added in the future.

Description: 

This paper in Science reports the synthesis of decamethyldizincocene, a stable compound of Zn(I) with a zinc-zinc bond. In the original LO, the title compound and the starting material, bis(pentamethylcyclopentadienyl)zinc, offer a nice link to metallocene chemistry, electron counting, and different modes of binding of cyclopentadienyl rings as well as more advanced discussions of MO diagrams. More fundamental discussion could focus on the question of what constitutes the evidence for a chemical bond, in this case, the existence of a zinc-zinc bond. In this updated LO, these topics are still covered, however additional topics, such as point group idenitifaction, details regarding the reaction mechanism, electronic structure, and  searching the literature using SciFinder are covered.  Additionally, electron counting is divided into both the covalent and ionic models.

Corequisites: 
Course Level: 
Learning Goals: 
  1. Students should become more confident reading the primary literature

  2. Students should be able to apply existing knowledge to interpret research results.

  3. Students should be able to apply electron counting formalisms to organometallic compounds.

  4. Students should be able to use 1H NMR spectroscopy data to rationalize structure.

  5. Students can rationalize bond distances based on periodic trends in atomic radii

  6. Students use SciFinder to put this work into a larger context.

  7. Students identify redox reactions based on oxidation changes.

  8. Students identify molecular point groups based upon structures.

  9. Students should be able to connect d electron count to observed colors of compounds. 

Related activities: 
Implementation Notes: 

Students are asked to read the paper and the accompanying Perspectives article before class as well as answer the discussion questions. The questions serve as a useful starting point for class discussion. 

Time Required: 
50 minutes

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