Kinetics

3 Jun 2017

An ion exchange method to produce metastable wurtzite metal sulfide nanocrystals

Submitted by Janet Schrenk, University of Massachusetts Lowell
Evaluation Methods: 

Evaluation methods are at the discretion of the instructor. For example, you may ask students to provide written answers to the questions, evaluate whether they participated in class discussion, or ask students to present their answers to specific questions to the class.

Description: 

In this literature discussion, students use a paper from the literature to explore the synthesis, structure, characterization (powder XRD, EDS and TEM) and energetics associated with the production of a metastable wurtzite CoS phase. Students also are asked define key terms and acronyms used in the paper; identify the goal of the experiments and determine if the authors met their goal. They examine the fundamental concepts around the key crystal structures available.  

 

Preserving Both Anion and Cation Sublattice Features during a Nanocrystal Cation-Exchange Reaction: Synthesis of a Metastable Wurtzite-Type CoS and MnS

Powell, A.E., Hodges J.M., Schaak, R.E. J. Am. Chem. Soc. 2016, 138, 471-474.

http://pubs.acs.org/doi/abs/10.1021/jacs.5b10624

 

There is an in class activitiy specifically written for this paper. 

Corequisites: 
Prerequisites: 
Learning Goals: 

In answering these questions, a student will be able to…

  • define important scientific terms and acronyms associated with the paper;

  • describe the rocksalt, NiAs, wurtzite, and zinc blende in terms of anion packing and cation coordination;

  • differentiate between the structure types described in the paper;

  • explain the difference between thermodynamically stable and metastable phases and relate it to a free energy diagram; and

  • describe the structural and composition information obtained from EDS, powder XRD, and TEM experiments.

Implementation Notes: 

This learning object was created at the 2017 IONiC Workshop on VIPEr and Literature Discussion. It has not yet been used in class.

Time Required: 
50 minutes
3 Jun 2017

Quantum Dot Growth Mechanisms

Submitted by Chi Nguyen, United States Military Academy
Evaluation Methods: 

The question document attempted by students in preparation for the literature discussion will be due prior to the in-class discussion. In particular, students' performance on the particle-in-a-box question will be evaluated to assess retention from the previously covered course material. The next exam following the discussion will contain specific question(s) (data/figure analysis) addressing these topics. Students' performance difference between the two will be evaluated. The extent to which students improve their post-discussion understanding of the concepts will direct future implementation.

Evaluation Results: 

To be determined. This is a newly proposed literature discussion.

Description: 

This literature article covers a range of topics introduced in a sophomore level course (confinement/particle-in-a-box, spectroscopy, kinetics, mechanism) and would serve as a an end-of-course integrated activity, or as a review activity in an upper level course. The authors of the article employ UV-vis absorption spectroscopy of CdSe quantum dots as a tool to probe the growth mechanism of the nanoparticles, contrasting two pathways.

 

Reference:  DOI 10.1021/ja3079576 J. Am. Chem. Soc. 2012, 134, 17298-17305

 
Corequisites: 
Prerequisites: 
Learning Goals: 

Apply the particle in a box model to interpret absorbance spectra with respect to nanoparticle size.

 

Analyze the step-growth and living chain-growth mechanisms proposed in this paper.

 

Evaluate the kinetics as it applies to the step-addition.

 

Recognize and apply multiple scientific concepts in an integrative manner.
Implementation Notes: 

Sophomore level implementation:  Recommend focusing on select portions (e.g. Figures 1b, 2, 5 with corresponding text) of the paper rather than having students read the entire document.  The learning objects focus on select topics, such as particle-in-a-box, reaction mechanism, and kinetics in conjunction with absorbance spectroscopy.  This would be a good literature discussion resource for an end-of-course integrative experience that encompasses multiple topics from general chemistry and inorganic chemistry.  

 

Advance level implementation:  For an upper division course, incorporate the paper in its entirety early in the course as an assessment on students’ ability to integrate multiple concepts that they should have learned in general chemistry, organic chemistry, and physical chemistry.  To enhance the experience, accompanying the literature discussion on this paper with a laboratory experience by repeating the experimental and characterization procedures presented in the paper, and having students' compare their results with published results.  This also serves to enhance students’ scientific literacy by critically assessing the quality of the paper.

 

Excerpts of the paper and questions can be used on a graded event, or as lesson preparation for in class discussion.

 
Time Required: 
In-class discussion takes approximately 50 minutes with students having already read the paper and submitted their responses to the questions.
23 May 2017

Ligand based reductive elimination from a thorium compound

Submitted by Chip Nataro, Lafayette College
Evaluation Methods: 

This was developed after the semester in which I teach this material. I look forward to using it next fall and I hope to post some evaluation data at that point.

Description: 

This literature discussion is based on a paper describing the ligand-based reductive elimination of a diphosphine from a thorium compound (Organometallics2017, ASAP). The thorium compound contains two bidentate NHC ligands providing an opportunity to discuss the coordination of these ligands. The ligand-based reduction is very subtle and would be challenging for students to pick up without some guidance. The compound undergoing reductive elimination also presents an excellent introduction into magnetic nonequivalence and virtual coupling. In addition, the compounds presented in this paper provide the opportunity to do electron counting on f-block compounds. 

Prerequisites: 
Corequisites: 
Learning Goals: 

Upon completing this LO students should be able to

  1. Use the CBC method to count electrons in the thorium compounds in this paper
  2. Describe the bonding interaction between a metal and a NHC ligand
  3. Discuss magnetic nonequivalency and virtual coupling
  4. Describe ligand-based reductive elimination and rationalize how it occurs in this system
Course Level: 
Time Required: 
50 minutes
5 May 2017

SOP4CV - A Web Resource for Cyclic Voltammetry Information

Submitted by Gerard Rowe, University of South Carolina Aiken
Description: 

http://sop4cv.com/

This is a great website created by Dr. Daniel Graham (who has the distinction of publishing a paper featured on TOC ROFL) to give anyone a working understanding of cyclic voltammetry techniques, their physical background, and the interpretation of their results.  

Prerequisites: 
Corequisites: 
Subdiscipline: 
Learning Goals: 

Students will gain experience interpreting the basic features of cyclic voltammograms, including: half-potential, electrochemical reversibility, chemical reversibility, and scan rate dependence

Students will learn the physical origins of the "duck" shape of a reversible CV using the Nernst equation and diffusion concepts

Students will learn what analytical methods are available using CV

Implementation Notes: 

None yet.  I'm considering creating an activity using the information in this website, but for now I just wanted to share this resource.

25 Mar 2017

KINETICS - Computations vs. Experiment

Submitted by Teresa J Bixby, Lewis University
Evaluation Methods: 

- determine the activation energy of a reaction from an energy diagram

- determine the rate constant for the reaction from the activation energy

- determine the rate law and rate constant for a reaction from experimental data

 

These Learning Objectives will be assessed on a subsequent exam.

Evaluation Results: 

Most students did not have a problem determining the rate constant from the activation energy (from an energy diagram). From what mistakes there were, the most common mistake was choosing the wrong starting energy (choosing the product energy rather than the reactant energy to start). Most students were also able to determine the rate constant from experimental data, especially if there were clearly 2 experiments where only one reactant concentration was doubled for each reactant. Changing the factor by which the reactant concentration changed (1.3 for example), or including experimental data where two reactant concentrations changed at the same time, seemed to cause more problems. 

Description: 

<p>This activity has students use Spartan to build an energy diagram for an SN2 reaction as a function of bond length. The activation energy can then be used to determine the rate constant for the reaction. After a few intoductory questions to orient general chemistry students to the organic reaction (with a short class discussion), the instructions lead them step-by-step to build the energy diagram for CH&lt;sub&gt;3&lt;/sub&gt;Cl + Cl- --&gt; Cl- + CH&lt;sub&gt;3&lt;/sub&gt;Cl. Any questions about how to use the program or descriptions of the levels of theory are given during the class period. The questions, class discussion, and Spartan tutorial for the first reaction can be compelted in one 50 min period.&nbsp;</p><p>The rest of the activity is completed as an assignment. Other anions attack CH&lt;sub&gt;3&lt;/sub&gt;Cl and students consider which product is more stable. They also compare the computational rate constant for OH- attacking with a rate constant determined from experimental data. They find that Spartan is good for molecular modeling but the absolute value of the energies of the transition states are inaccurate.&nbsp;</p><p>SN2 reactions with more complex molecuels may be more illustrative.&nbsp;</p><p>In the future we hope to develop this activity into an in-class prelab where then students can collect the experimental data on their own.&nbsp;</p>

Learning Goals: 

- use Spartan to build molecules and a transition state

- determine the activation energy of a reaction from an energy diagram

- determine the rate constant for the reaction from the activation energy

- determine the rate law and rate constant for a reaction from experimental data

- relate reactant and product energies to leaving group character

- compare computation to experiment

Prerequisites: 
Corequisites: 
Equipment needs: 

Need to have access to Spartan Student.

Topics Covered: 
Course Level: 
Subdiscipline: 
Implementation Notes: 

Building the transition state seems to be the most confusing part for General Chemistry students who have not used Spartan before. Encouraging them to limit twirling the molecule around a lot before they have completed this step seems to help. I intend to clarify these instructions before the next implementation. 

A different base molecule may yield better agreement with experimental data. This will aslo be explored before the next implementation.

Time Required: 
50 min + out-of-class assignment (~5 days)
21 Feb 2017
Evaluation Methods: 

Graded problems students turned in.

Informal evaluation during discussion.

Evaluation Results: 

Graded assignments: mean of 84, std dev of 12, so a fairly broad range of understandings

Informal: Students really enjoyed getting to evaluate published work critically and were quite engaged in discussions, which helped to bring some of the students who didn't understand the paper as well up to speed.  After the paper, students have felt much more comfortable questioning what is stated in papers, particularly if little or no support is given.

I will definitely use this again!  Unfortunate to find a paper with several important oversights in the literature, but it is a good learning opportunity.

Description: 

This LO is a problem-set-style literature discussion that leads students through a critical analysis of an interesting but flawed paper from the recent chemical literature.  Students use the questions to help them work through the paper prior to class, providing plenty of raw material for an in-class discussion about various aspects of the work from a mechanistic organometallic perspective.  The questions help students critically analyze substrate tables, spectroscopic data, and computational results from DFT.

Corequisites: 
Course Level: 
Learning Goals: 
  • Students will be able to pull out important mechanistic information from substrate tables in an organometallic paper
  • Students will be able to use knowledge of organometallic mechanisms and organic chemistry to rationalize findings in a catalysis paper
  • Students will be able to use knowledge of spectroscopy, particularly NMR, to understand structure and bonding arguments in an organometallic paper
  • Students will critically analyze a paper and learn to feel comfortable questioning assertions by authors, including the major findings of a paper
Implementation Notes: 

I had students prepare answers to these questions ahead of class and bring the answers with them.  To add incentive, I collected them as a homework assignment (though I graded some of the harder ones fairly leniently).  The questions helped prepare them for a class discussion of the paper, which I led with a few slides containing information from the paper and some other useful tidbits (I am happy to send those to you if you like, just contact me).

Time Required: 
1-2 hours student prep (reading paper); 45 minutes in class discussion
4 Jan 2017
Description: 

This is a great new textbook by George Luther III from the University of Delaware.  The textbook represents the results of a course he has taught for graduate students in chemical oceanography, geochemistry and related disciplines.  It is clear that the point of the book is to provide students with the core material from inorganic chemistry that they will  need to explain inorganic processes in the environment.  However the material is presented in such a clear, logical fashion and builds so directly on fundamental principles of physical inorganic chemistry that the book is actually applicable to a much broader audience.  It provides a very welcome presentation of frontier orbital theory as a guide to predicting and explaining much inorganic chemical reactivity.  There are numerous very  helpful charts and tables and diagrams.  I found myself using the book for a table of effective nuclear charges when I was teaching general chemistry last semester.  The examples are much more interesting that the typical textbook examples and would be easy to embellish and structure a course around.  There is also a helpful companion website that provides powerpoint slides, student exercises and answers.  The book covers some topics not typically seen in inorganic textbooks like the acidity of solids but the presentation of this information makes sense in light of the coherent framework of the text.  We so often tell our students "structure dictates function".  This text really make good on that promise.  My only complaint is that I wish the title were something more generic so that I could use it for a second semester of introductory-esque material that we teach after students have taken a single semester of intro chem and two semesters of organic chemistry.  So much of what is covered in this textbook is precisely what a second semester sophomore chemistry major should know before proceeding on in the major.  But the title makes the book hard to sell to chemistry majors and that is regrettable. 

Prerequisites: 
Course Level: 
28 Dec 2016

Isotope Effects in Arene C-H Bond Activation by Cp*Rh(PMe3)

Submitted by Adam R. Johnson, Harvey Mudd College
Evaluation Methods: 

This LO was used in class to help a student guide a discussion of the paper. We did not cover all of the LO in a 75 minute class period, as we let the discussion take us where it wanted to. 


A better way to ensure student preparation would be to collect the questions at the beginning (or end, if they wanted to use their notes in class) of class to ensure that they had really studied the paper.

Evaluation Results: 

I used this LO as a guided reading handout and did not collect the answers so I do not have any assessment data at this time.

Although my students found this paper to be relatively dense and hard to follow at times. The paper separates out the Results and Discussion sections, so at times it seems repetitive. However, once they had worked their way through the paper, the students found the results interesting and the methods informative. We were able to discuss it at a high level in class.

Description: 

This literature discussion is based on a paper by Bill Jones and Frank Feher (J. Am. Chem. Soc., 1986, 108, 4814-4819). In this paper, they study the activation of aromatic C-H bonds by a rhodium complex. Through careful experimental design, they were able to examine isotope effects on the selectivity of the reaction. Analysis of the rate data allowed them to prepare a reaction coordinate free energy diagram. This paper also introduces the effects of C-H bond breaking in early or late transition states on the vibrational energy spacing at both ground and excited states. The paper is a good way to bring kinetic isotope effects into the classroom. The paper also introduces the concept of deuterium labeling experiments and what that information can tell you.

An important aspect of this paper, and what makes it so interesting, is that they are able to get two kinetic isotope effects, one for each step of the reaction. From these two KIEs alone they are able to determine the unexpected rate-determining step of the reaction. It is a triumph of mechanistic investigation into intermediates that are undetectable.

This LO presents a series of guided reading questions that help a student approach and understand the material presented in the paper in a more thorough way. Part one is a guided inquiry that allows the students to derive and understand differing zero point energies for proteated and deuterated compounds. Part two guides students  through the results presented in the paper to help them better understand how experimental data can be used to understand the mechanism of a chemical reaction. There is more to the paper than kinetic isotope effects, but that is the focus I chose while developing it. The LO is suitable for junior or senior undergraduates in an organometallics course or unit within an inorganic course.

I would like to acknowledge Ryan Pakula and Joanne Redford from my Chem 165 course in 2008 who wrote early versions of some of the questions about vibrational states, and a careful critical read by Nancy Williams, who understands this stuff at a much deeper level than I do.

Course Level: 
Learning Goals: 

upon completing this LO students should be able to
:
1. calculate and interrelate reduced mass, vibrational frequency, force constant, and zero point energies for vibrational states of bonds
2. define kinetic isotope effects (normal, and inverse)
3. calculate/predict/estimate a normal and inverse KIE for a chemical reaction from IR data.
4. interpret and describe a reaction coordinate diagram for a chemical reaction
5. count and classify metal complexes using CBC method

Subdiscipline: 
Implementation Notes: 

I used this LO as a guided reading handout for a senior-level organometallics class. The questions and the paper were provided to the students a week in advance and the in-class activity was a student-led discussion of the paper.

Time Required: 
1 50-75 minute class period for discussion
28 Dec 2016

Understanding the Mechanism of Grubbs-Catalyzed Olefin Metathesis

Submitted by Richard Lord, Grand Valley State University
Description: 

A literature discussion has been developed for two courses: (i) a more basic set of questions appropriate for a sophomore level course or, possibly, a one semester upper level course that does not spend much time on organometallics, and (ii) an in-depth, in- and out-of-class set of assignments appropriate for an organometallics unit or course. Both sets of questions explore the mechanism of olefin metathesis in first- and second-generation Grubbs catalysts using a variety of spectroscopic kinetic techniques that were presented in the paper Sanford, M. S.; Love, J. A.; Grubbs, R. H. J. Am. Chem. Soc. 2001, 123, 6543-6554 (doi: 10.1021/ja010624k).

Corequisites: 
Prerequisites: 
Subdiscipline: 
Learning Goals: 

A student should be able to do the following after completing this LO:

Identify and discuss the importance of an olefin metathesis reaction.

Distinguish between Fischer- and Schrock-type carbenes and count electrons in complexes featuring these ligands.

Predict Ia vs. Id mechanisms based on electron counting.

Discuss why 31P and 1H NMR, and UV-Vis, were appropriate spectroscopic techniques for measuring kinetics in these systems.

Explain how variations in the catalyst (halide, carbene substituent, phosphine substituent, phosphine vs. NHC, etc.) affect ligand exchange.

Describe why the second-generation catalysts outperform the first-generation catalysts based on olefin binding vs. phosphine loss (in contrast to the historical reasons for their design), and why trans- effect arguments do not apply to the Grubbs system.

 

 

Implementation Notes: 

Two of us ran portions of these (they were not complete) in Fall 2016. Both of us noted that students were confused by the NHC representation in the manuscript because the authors assume that the reader knows there is no H on the carbene carbon, yet one would predict a H there based on the line structure formalism.

It is important to point out to students that the work here represents only the first 1-2 steps of the overall mechanism of olefin metathesis. There is a question in both the basic and advanced exercises that has students analyze the metallacyclobutane intermediate, but this species is formed later in the mechanism than any of the work presented here.

Time Required: 
~1 class period
28 Dec 2016

Virtual Issue of Organometallics

Submitted by Chip Nataro, Lafayette College

You can find the virtual issue with our editorial and all of the papers here.

Subdiscipline: 
Prerequisites: 
Corequisites: 
Course Level: 

Pages

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