Upper Division

9 Oct 2019

Fourier Transform IR Spectroscopy of Tetrahedral Borate Ions

Submitted by Zachary Tonzetich, University of Texas at San Antonio
Evaluation Methods: 

The students perpare laboratory reports displaying their data in proper format with each peak labeled. The report must also contain answers to all of the quetions posed in the manual. Student performance and learning is assessed by the qualtity of their written reports and by a separate quiz covering aspects of vibrational spectroscopy. Teaching assistans also ensure that students' data acquisition is performed in a satisfactory manner during the laboratory period.

Evaluation Results: 

Students typically have great difficulty connecting the idea of normal modes, their symmetries, and why we observe IR peaks. They approach IR spectroscopy in much the same way they do NMR spectroscopy (i.e. methane shows four equivalent C-H bonds so I expect one C-H stretching motion) leading to serious misconceptions. This laboratory was designed in part to dispell these misconceptions. Question 1 addresses this issue most directly and many of the class answer incorrectly.

The questions in the laboratory involving harmonic oscialltor analysis are generally more straightforward for students as they just need to use the correct equations. Most of the class answers these correctly.

Likewise, students generally understand that vibrational frequencies are inversely proportional to the mass of the atoms involved in the vibration and are there able to make connections between the observed spectra of BH4-, BD4- and BF4-.

Aspects of functional group analysis are more familiar to students and they generally have little trouble assigning the spectrum of tetraphenylborate.

Description: 

This experiment was developed for an upper division Instrumental Analysis course to give students additional experience with infrared (IR) spectroscopy beyond the routine functional group identification encountered in undergraduate Organic Chemistry courses. It shares some aspects with the analysis of gas phase rovibrational spectra typically performed in Physical Chemistry courses, but places a greater emphasis on more practical considerations including data acquisition (using ATR) and interpretation. The molecular ions used in the experiment also demonstrate tetrahedral symmmetry which allows for topics in Group Theory to be exploited.

The experiment has students record the spectra of several tetrahedral borate ions including the isotopomers NaBH4 and NaBD4. The students then analyze their data in the context of the symmetry of normal modes, the harmonic osciallator model, comparisons with Raman spectra, and functional group composition. Post lab questions guide students through each of the topics and ask them to make quantative and qualitative predictions based on their data and theoretical models of molecular vibration.

Course Level: 
Learning Goals: 

-Students should be able to understand the relationship between molecular structure, normal modes, and peaks in the IR spectrum. This is a major misconception with students as they tend to believe that the presence of four B-H bonds in the borohydride ion will neccessary mean that four peaks (or one since they are equivalent) will be observed by IR. Unlike NMR spectroscopy, there is no 1:1 correspondence between the number of equivalent bonds and the number of peaks observed in the spectrum.

-Students should also be able to apply their knowledge of theoretical models (quantum harmonic oscillator) to quantitaively intrepret IR spectra and predict the energy of transitions that cannot be observed due to instrumental limitations.

-Students should be able to understand at a qualitative level how the masses of atoms affect the energy of molecular vibrations.

Equipment needs: 

The only required piece of equipment beyond the chemicals is an infrared spectrophotometer. At our institution we use an ATR element to acquire the data, but KBr pellets or nujol mulls should work equally well. All chemicals were purchased from Sigma-Aldrich and are of reasonable price.

Implementation Notes: 

See attached file with more details. The data acquisition is very straightforward if ATR sampling is employed. Students need only use the instrument for about 15 - 20 minutes to record all four samples.

Time Required: 
30 minutes to 2 hr depending upon the number of students.
29 Jul 2019

Introduction to Drago's ECW Acid-Base Model

Submitted by Colleen Partigianoni, Ferris State University
Description: 

This LO was created to introduce Drago’s ECW model, which is an important contribution to the discussion of Lewis acid-base interactions. Unlike the qualitative Pearson’s HSAB model (Hard Soft Acid-Base model,) the quantitative ECW model can be used to correlate and predict the enthalpies of adduct formation and to obtain enthalpy changes for displacement or exchange reactions involving many Lewis acids and bases.  Unlike all other acid-base models, graphical displays of the ECW model clearly show that there is no one order of acid or base strengths, and illustrate that two parameters are needed for each acid and base to provide an order of acid or base strength.  The ECW model can also provide a measure of steric strain energy or pi bonding stabilization energy accompanying adduct formation, which is not possible with any other acid-base model. 

This set of slides is intended to provide a basic introduction to the model and several examples of predicting energy changes using the model. It also illustrates how to construct and interpret a graphical display of the model.

 It should be noted that this LO is not in the PowerPoint format, but instead is a more extensive set of notes for instructors who are not familiar with the ECW model. It could be condensed and rewritten in the more standard PowerPoint format.

There is also an ECW problem set LO that can used to supplement this LO.

Prerequisites: 
Corequisites: 
Learning Goals: 

After viewing the slides, students, when provided with appropriate data, should be able to:

  • Calculate sigma bond strength in Lewis acid-base adducts using Drago’s ECW model.
  • Show how to deal with any constant energy contribution (W) to the reaction of a particular acid (or base) that is independent of the base (or acid) when an adduct is formed.
  • Garner information regarding steric effects and pi bond stabilization energy in Lewis acid-base adducts using the ECW model.
  • Show using a graphic display of ECW that two parameters for each acid and each base are needed in acid-base models to determine relative strengths of donors and acceptors.
Evaluation
Evaluation Methods: 

This LO has not been used yet and evaluation information will be posted at a later date.

25 Jul 2019

1FLO: One Figure Learning Objects

Submitted by Chip Nataro, Lafayette College
Corequisites: 
27 Jun 2019

Porphyrin-Based Metal-Organic Frameworks

Submitted by Amanda Bowman, Colorado College
Evaluation Methods: 

Students completed this activity in small groups, then turned in individual worksheets. Student learning and performance were assessed through 1) in-class group discussion after they had worked on the activity in small groups, and 2) grading the individual worksheets. Participation was most important in the small-group portion.

Evaluation Results: 

In general, students really enjoyed this exercise and felt that it was helpful for visualizing metal-organic frameworks (particularly the extended 3D structure). They also generally felt that it was helpful in visualizing the bonding sites of metal vertices, particularly for thinking about how that influences potential reactivity. We used Mercury as a visualization software for this discussion, and the majority of students felt very comfortable using Mercury and looking at cifs on their own after this activity.

 

The biggest challenge for students seemed to be in relating the 3D structure in the cif to the images and chemicals formulas in the article. They also tended to need some hints about question 5 – to think about what information Mössbauer can provide about oxidation state of the metal, or that you can tell whether or not there are two distinct iron environments. In our class, we do brief units on X-ray crystallography including how to use and interpret cifs, and Mössbauer spectroscopy before this literature discussion. If those topics are not already addressed in a particular class it might be helpful to add them in or directly address those topics for the students as an introduction to the literature discussion.

Description: 

This literature discussion explores the physical structures, electronic structures, and spectroscopic characterization of several porphyrin-based metal-organic frameworks through discussion of “Iron and Porphyrin Metal−Organic Frameworks: Insight into Structural Diversity, Stability, and Porosity,” Fateeva et al. Cryst. Growth Des. 2015, 15, 1819-1826, http://dx.doi.org/doi:10.1021/cg501855k. The activity gives students experience visualizing and interpreting MOF structures, and gives students exposure to some of the methods used to characterize MOFs.

Corequisites: 
Course Level: 
Learning Goals: 

Students will be able to:

  • Interpret and describe the bonding and structural characteristics of MOFs
  • Apply knowledge of ligand field strength to electronic structure of MOFs
  • Analyze X-ray crystallographic data to gain information about structural characteristics of MOFs
  • Interpret Mössbauer spectra to gain information about electronic structure of MOFs
Implementation Notes: 

This literature discussion was designed for use in an advanced (upper-level) inorganic chemistry course, but could be used in a foundational inorganic course if students have already been introduced to d-splitting diagrams and are given some coverage of Mössbauer spectroscopy and X-ray crystallography. When covering MOFs in class, students frequently expressed that visualizing and understanding the bonding sites and extended 3D structures was very challenging. So, this literature discussion was developed specifically to address that. Students completed this activity in small groups. It is very helpful to advise students ahead of time to bring laptops (or instructor should have some available) and to have the cifs from the paper downloaded and ready to go. We used Mercury as a visualization software for this activity. This activity can easily be completed in one class period. It is also helpful if students have been provided with the article ahead of time and encouraged to look it over – otherwise the most time-consuming part of this activity was allowing time for students to examine the MOF structure images in the paper before being able to discuss and answer the questions with their groups.

Note on visualization of MOFs using Mercury: To answer the discussion questions, we used the ‘stick’ or the ‘ball and stick’ style. We also used the default packing scheme (0.4x0.4x0.4) and the 1x1x1 packing scheme. The packing scheme can be changed by selecting Packing/Slicing… in the Calculate menu. I also had students view the 3x3x3 packing scheme – while this is not necessary to answer the discussion questions, it was interesting for students to be able to visualize the extended structure of the MOFs.

 

9 Jun 2019

An improved method for drawing the bonding MO for dihydrogen

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

When I do this correctly, the students don't accidentally see something which may make immature students giggle.

Evaluation Results: 

I have had multiple colleagues tell me that this technique worked for them and saved them from repeating an embarassing classroom event.

Description: 
Most of us have probably been there. Discussing homonuclear diatomic MO diagrams and on the first day you want to put up the sigma bonding molecular orbital for H2. If you teach it like me, you emphasize the LCAO-MO approach, so you draw a hydrogen atom with its 1s orbital interacting with a hydrogen atom with its 1s orbital...and then you notice giggling from the less mature audience members. My technique will help to prevent this from happening. The technique is in the "faculty only" files section.
Learning Goals: 

The instructor will draw the bonding MO of dihydrogen without accidentally causing laughter in the class or self embarassment.

Corequisites: 
Equipment needs: 

chalkboard or whiteboard

ability to adjust quickly just in case

Prerequisites: 
Implementation Notes: 

I have come close to accidentally drawing the incorrect version of this diagram and I am able to stop myself quickly as illustrated in the instructions. 

Time Required: 
a minute to learn, a lifetime to master.
9 Jun 2019

Chem 165 2018

Submitted by Adam R. Johnson, Harvey Mudd College

This is a collection of LOs that I used to teach a junior-senior seminar course on organometallics during Fall 2018 at Harvey Mudd College. There were a total of 9 students in the course. The Junior student (there was only one this year) was taking 2nd semester organic concurrently and had not takein inorganic (as is typical).

Subdiscipline: 
Corequisites: 
Course Level: 
9 Jun 2019

1FLO: PCET and Pourbaix

Submitted by Anne Bentley, Lewis & Clark College
Evaluation Methods: 

I graded each student’s problems as I would any other homework assignment, and they averaged about 80% on that part of the assignment. The other half of the total points for the assignment came from in-class participation.

Evaluation Results: 

We had a rich conversation about this article in class; it was probably one of the most interesting literature discussion conversations I’ve had. Although this was the only introduction to Pourbaix diagrams in the course, 12 of 15 students correctly interpreted a “standard” Pourbaix diagram on a course assessment.

 

Description: 

This set of questions is based on a single figure from Rountree et al. Inorg. Chem. 2019, 58, 6647. In this article (“Decoding Proton-Coupled Electron Transfer with Potential-pKa Diagrams”), Jillian Dempsey’s group from the University of North Carolina examined the mechanism by which a nickel-containing catalyst brings about the reduction of H+ to form H2 in non-aqueous solvent. Figure 3 in the article presents an excellent introduction to the use of Pourbaix diagrams and cyclic voltammetry to determine the mechanism of a proton-coupled electron transfer reaction central to the production of hydrogen by a nickel-containing catalyst.

Corequisites: 
Course Level: 
Learning Goals: 

Students should be able to:

-  identify atoms in a multidentate ligand that can coordinate to a metal as a Lewis base

-  outline the difference between hydride addition to a metal and protonation of a ligand in terms of changes to the overall charge of the complex

-  analyze a Pourbaix diagram to predict the redox potential and pKa of a species

Subdiscipline: 
Implementation Notes: 

I have discussed the challenge of integrating literature discussions into my inorganic course in a BITeS post and the VIPEr forums. Each spring I try something a little different. This year I used three articles from the literature to frame our review of course material at the end of the semester, with each literature discussion occupying a one-hour class meeting.

In each case, the students completed problems before coming to class. While these problems were based on the journal articles, they did not require the students to read / consult the journal articles in order to complete the assignment. The students brought an electronic or paper copy of the article to class. I usually put students in groups (approximately 3 per group) and gave each group new questions to work on, which did draw from the article. After some time working in groups, each group presented their material to the rest of the class.

In implementing this particular literature discussion, I didn’t have any further questions for them.  I walked through some of the other figures from the article (especially Figure 1).  We discussed the authors’ use of color in creating Figure 3. We also reviewed the significance of horizontal vs vertical vs diagonal lines. Because I had not covered Pourbaix diagrams in the course, the activity was a good introduction to the concept.

Because these problems don’t require consultation with the article, they are suitable to use on an exam.

Time Required: 
varies
9 Jun 2019

Triphenylphosphine: Transformations of a Common Ligand

Submitted by Bradley Wile, Ohio Northern University
Evaluation Methods: 

This lab report is graded using the attached rubric (see faculty files). 

Evaluation Results: 

Over the last four iterations of this lab, the average total score was ~42/50 (n = 21). Students are generally good at recognizing that a redox process is occurring, though some struggle with this realization. Most students generate a Lewis structure with a dative bond, though some do not use the MO diagram to infer a reasonable direction for the dative interaction. I typically work through this with the students, asking them questions like "which orbitals have electrons?" and "what orbitals are interacting in your Lewis depiction?" This has been a good introduction to these synthetic and instrumental methods, and gives the lab partners an opportunity to divide up their responsibilities.

Description: 

This experiment tasks students with preparing triphenylphosphine sulfide, and the corresponding I2 adduct, then characterizing these products using common instrumental methods. Students are asked to consider MOs and tie this to their Lewis bonding depiction for the final product. This discussion is supported by WebMO calculations and tied to the experimental data obtained by the student.

If you would like to use this lab, please complete the feedback form (faculty files) and let me know how you adapt it. I would like to publish this procedure (eventually), and I am open to collaborative projects to get this to the best final form.

Course Level: 
Prerequisites: 
Topics Covered: 
Learning Goals: 
After completing this lab report, students should be able to:
  • Construct an MO diagram for I2, and relate this to the bonding in the Ph3PS-I2 complex
  • Using MO theory as a basis, decide on the best Lewis representation for Ph3PS-I2
  • Discover the wealth of bonding modes within main group species
  • Identify changes in the observable spectra for P(III) and P(V) compounds
  • Search and reference the primary chemical literature using correct ACS reference formatting
 
Subdiscipline: 
Corequisites: 
Equipment needs: 

This experiment is run using our in house instumentation including:

  • NMR spectrometer capable of acquiring 1H and 31P spectra
  • IR spectrometer
  • UV-vis spectrometer (we acquire data on a Spec200 that works just fine for this)
  • GC-MS (optional)

These spectra are provided as faculty files. If you do not have any of these capabilities, the spectra may be given to students as a handout.

Additionally, the experiment will require use of round-bottomed flasks, condensers, beakers, scintillation vials, hot plates, and gravity filtration apparatus (stemless if hot filtration required). Solvents and reagents are typically already present in the department, or may be purchased at reasonable cost.

Implementation Notes: 

I use this lab as the first experiment of the semester, and begin the first week's activity after the introduction and lab safety discussion. 

Prior to running the experiment, I prepare approximately one batch of each product (Ph3PS and Ph3PS-I2) in case of a laboratory mishap. The products are indefinitely stable under ambient conditions.

I do not describe the reaction as a redox process, or suggest a bond order (i.e. I try to write the formula for Ph3PS with an ambiguous bond order, as shown here). 

Depending on the age of your bottle of Ph3P, you may spot a small quantity of Ph3P=O in the 31P spectrum (small peak around 30 ppm in the included spectrum). This may be an opportunity to discuss connections to biochemistry or atmospheric oxidation, or ask students to draw Lewis depictions of these species. 

I teach my students how to manually run their own NMR spectra using TopSpin at this point (they have previously learned 1H and 13C using the autosampler). I typically discuss the differences between 31P{1H} and 31P (non decoupled) spectra at this time. Note that the lab handout has some instructions specific to the Bruker software that may be updated if you use a different spectrometer.

Literature articles describing the crystal structure of the final adduct (and related I2 species) are linked here. I have not typically gone into great detail about this, as the assembled I2 ribbons can confuse the students that are just putting the basic concepts together.

Time Required: 
Two full 3 hour labs, and approximately 1 additional hour (first week). If characterization is done outside of normal lab hours, this could be accomplished in one full 3 hour lab and one additional hour.

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