MO Theory? NO Problem

Students at Western Washington University are first introduced to the concept of molecular orbital theory in Organic Chemistry I. It is briefly mentioned in the general chemistry textbook, but it is excluded from covered content in first year classes. First year chemistry students are introduced to the concept of atomic orbital hybridization, but with surface level learning objectives. Objectives are typically assessed by simply having the student label the hybridization of a specified atom. Because of such a limited exposure, most students find themselves completely overwhelmed with the topics of hybridization of atomic orbitals and molecular orbital theory when they get to organic chemistry. Historically, the topics are covered at the beginning of the year-long series, only to be forgotten and rarely (if at all) applied to the numerous reactions that are covered. Feedback from past students has included statements of, “I just memorized how to assign hybridization, I don’t actually know what it means” and “Molecular orbital theory was the most confusing part of the course, I still don’t know why we learned it.”

A big contributor to this lack of deeper understanding and application is the limited coverage and explanation in the textbook. The functional group-based text, previously used at this university, included ten pages of text and three in-chapter problems concerning atomic orbital hybridization and molecular orbital theory. Karty devotes an entire chapter to these concepts! Chapter 3 (“Orbital Interactions 1: Hybridization and Two-Center Molecular Orbitals”) includes 23 pages of text and images, and 22 in-chapter practice problems. In this chapter, the students are learning the importance of hybridization and molecular orbital theory and how the hybridized atomic and molecular orbitals are generated.

Molecular orbital theory in the text gets even better. The theory is revisited in Interchapter 1 (“Molecular Orbital Theory and Chemical Reactions”), which would not make much sense in a functional group-based text, and is applied to the nine elementary steps covered in Chapter 7 (“An Overview of the Most Common Elementary Steps”). These 9 elementary steps are the basis for the entire text and course. The students will learn to apply these basic mechanistic steps to any set of reagents and reaction conditions given. That alone is an incredible improvement from the previously taught functional group-based text, but in addition, the students are acquiring a deeper understanding of why and how these mechanisms actually take place.

The most encouraging feedback about this improved method of teaching and applying molecular orbital theory came from a previous student who learned from the functional group-based text and is currently the lead organic chemistry tutor at the tutoring center. She said, “I was able to get by in organic chemistry by memorizing how to assign hybridization. Now, the students who are coming to the tutoring center have in-depth questions about how to hybridize and form molecular orbitals and I honestly didn’t know the answers. I had to go to the new text and learn the content, but now it makes so much more sense.”

Not only have we improved our approach to teaching organic chemistry by switching to a mechanistically-organized text and course, but we are also expanding the student’s knowledge about why the mechanisms are actually occurring.

-Jennifer Griffith, Western Washington University
Click here to learn more about Prof. Griffith

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