Alison Flynn’s latest in the Journal of Chemical Education is an instant classic. She describes a redesign of the organic chemistry curriculum at the University of Ottawa that tackles head on the issue of “curved arrows as decorations” that has been well documented by Cooper, Bhattacharyya, and others.
Her approach begins with four units on the basics of organic structure and physical properties, which is standard stuff. An entire unit on reaction mechanisms that precedes the first reaction covered comes next, and this is really the pièce de résistance of the design. Acid-base reactions come next (pretty standard), followed by nucleophilic additions to π electrophiles and electrophilic addition to π electrophiles, including reactions of alkenes and arenes. That’s organic 1. Note the complete absence of substitution and elimination—a huge plus in my opinion!
Organic 2 begins with eliminations and oxidations—love how these two are grouped together, as many oxidations are glorified eliminations. Next come activated π nucleophiles (enols and enolates), π electrophiles with a leaving group (e.g., acid chlorides), and π electrophiles with a “hidden” leaving group (e.g., imine formation). Seems a little odd to loop back to carbonyl chemistry at the end of organic 2 after hitting nucleophilic addition to carbonyls near the beginning of organic 1, but let’s not allow “we’ve always done it this way” to rationalize away the change.
The paper describes a few interesting little changes and ideas. For example, the authors avoid the use of “R” in generalized figures—opting instead to just use lines—to reduce visual clutter. They also mention one of my favorite principles in organic chemistry: “The role of the [basic or acidic] catalyst— activating nucleophile or electrophile [respectively]—is a pattern that is consistent throughout organic chemistry.” These days, biochemistry majors need to absorb this deeply in organic to understand how enzyme catalysis works; unfortunately, it’s tough to make it stick…from personal experience!
The key unit on the electron-pushing formalism (EPF) and mechanisms, Unit 5, emphasizes principles that are obvious to expert chemists, but which students often forget:
- Curved arrows imply products. They’re a system for bookkeeping.
- Electrons are conserved in reaction mechanisms. If they appear or disappear between steps, something’s wrong.
The authors mention three key learning goals for the unit. The first two are purely algorithmic in essence: (1) draw products given reactants and curved arrows; (2) draw curved arrows given reactants and products. The third, which in my opinion is overly ambitious for this early in the game, is (3) draw curved arrows and products given the starting materials for a new reaction. It seems out of place, given the emphasis of the other two goals on getting students comfortable with the way the formalism works. I’d instead opt for a look at either frontier MO theory, or localized NBO theory, or both—giving students the tools to predict reactivity from structure.
I wouldn’t call this approach ideal (it needs an element of localized orbital theory, in my view), but it’s a huge step in the right direction. This curriculum systematizes organic reaction mechanisms and presents them in a way that’s designed to fit neatly in the brain. I think students will respond positively to that in the long run, and you’ll see more and more faculty implementing their courses this way.