Stereochemistry and Adaptability

The three dimensional nature of organic molecules is a topic that all organic chemistry courses must cover. Chairs, Newman projections, Fischer projections, rotations, conformational changes, and stereochemistry are very challenging for sophomore students to grasp—especially if this is their first exposure to the concept that structure is a key element to reactivity. That said, watching students take the stereochemistry exam is very entertaining! The students problem-solve by rotating the paper to “see” a perspective better, hold up their hands and rotate them to visualize stereocenters, and even turn pages over to better view the mirror image. It is a rare opportunity for a faculty member to see student problem-solving in real time.

I imagine that stereochemistry is one of the biggest challenges for any textbook author to tackle. Any approach is going to, by the very nature of a text, commit to a singular process of solving problems of “what is the relationship between these two molecules?” Karty has chosen the path of asking students to visualize these relationships. This requires students to see, really see, that two molecules are mirror images of one another if they are enantiomers. For many of my students, with practice, they are able to picture these compounds and solve the problem. The examples in Karty are excellent, and I find that most of these students respond positively to the visuals in the text. However, I have found that there is always a subset of students, about 40% for me, that are unable to mentally manipulate molecules with confidence. In my twenty years of teaching, I have also found that this mental manipulation is not an accurate measure of overall success in organic chemistry, chemistry in general, or further pursuits that lie in other disciplinary areas.

Continue reading

Taking the Fear Out of Lengthy Mechanisms: A Good Type of Problem from Chapter 7

Even if a student intends to devote a great amount of time and effort to studying mechanisms and to using mechanisms to understand reactions, their efforts can be easily thwarted by the sheer intimidation of relatively long mechanisms. Years ago, when I was still teaching under a functional group organization, I would hear gasps and groans from my students—even my better students—each time I worked through a mechanism having as few as six, five, or four steps. Nowadays, learning under a mechanistic organization, my students take these kinds of “lengthy” mechanisms in stride, and I think a lot of it has to do with the preparation they receive from one of my favorite types of problems in Chapter 7. A good example is Problem 7.30, which deals with a Fischer esterification reaction:

Continue reading

Molecular Modeling Kits

For many students, the three-dimensional nature of organic chemistry raises the difficulty of the course to a new level. This difficulty stems from the fact that the three dimensionality of a molecule is depicted on a two-dimensional surface using any of a variety of representations. Accepted representations include dash-wedge notation, sawhorse projections, Newman projections, Fischer projections, Haworth projections, and chair representations. Even some of the most basic problems in organic chemistry may require a student to convert a two-dimensional representation of a molecule into three dimensions, carry out a particular manipulation of the molecule, and then return the molecule back to a two-dimensional representation in order to provide an answer. Some students can carry out these tasks in their head with no trouble, but I have found over the years that the large majority of students cannot. So then, how do we help these students?

Continue reading