Taking the Enolate off the Pedestal

I’ve noticed over the years that when I put a “name” on something, students tend to panic. We will be doing just fine with SN2 reactions, but when I suddenly name it the Williamson Ether Synthesis, my students become very concerned, as if it’s some completely different concept. Whenever I bring up the Williamson Ether Synthesis later in the course, they don’t know what I’m talking about and suddenly can’t do a straightforward SN2 reaction anymore. Perhaps you have noticed this with other named reactions, too.

A similar thing would happen about midway through second semester when we would start dealing with the reactions of enolates, which was usually given its own chapter in the text. Even though it’s just another nucleophile, students became very concerned with this “new” entity. Students compartmentalized it into its own arena where it looked and acted differently from every other reaction they’d seen before. They thought they had a completely different set of confusing reactions. We had put the enolate on a pedestal. Yet when my department switched to Karty’s text, I suddenly noticed my students no longer really had a problem with enolates. Karty has taken the enolate off of the pedestal.

In Karty, there is no special enolate chapter. They are first introduced in Chapter 10, the second chapter dealing with nucleophilic substitution and elimination reactions. The logic follows nicely: If deprotonating an alpha carbon generates just another nucleophile, and if nucleophiles can undergo SN2 reactions, then what if we use an enolate in an SN2 reaction? This is mechanistically no different than deprotonating an alcohol to make a stronger S­N2 nucleophile in an alkoxide (which we do all the time anyway). Conceptually, why should it be any different with an alpha carbon?

Now, instead of waiting for enolate alkylation until the start of the special chapter on enolates, the enolate fits quite nicely in the SN2 unit. Students recognize the similarities in the mechanisms, they assimilate the reaction easily into their growing reaction database, and I now get another carbon-carbon bond forming reaction first semester that I previously couldn’t use until second semester.

The same scenario plays out second semester. If nucleophiles attack aldehydes and ketones, and an enolate is just another nucleophile, why do we need a special chapter to deal with enolates attacking aldehydes and ketones? Instead, the aldol reaction is folded nicely into the rest of the chapter dealing with nucleophilic addition to polar pi bonds. The Claisen condensation follows the same logic.

It just makes sense. I had been banging my head against the wall trying to help my students decode the seemingly scary enolate, when mechanistically it’s really no different than any other nucleophile. So stop putting the enolate on a pedestal. It’s time to treat the enolate like the common nucleophile it has always been.

-Adam Azman, Butler University

Click here to learn more about Prof. Azman

2 comments on “Taking the Enolate off the Pedestal

  1. Martin Walker
    February 23, 2016 at 11:56 pm #

    Yes, I agree – that’s exactly what I’ve found with enolates! Karty’s book is a great help in that regard.

    However, I do find my students seem to respond to “Williamson ether synthesis”, though of course it’s introduced just as an example of SN2. It’s value is when I give them a synthesis problem with an ether target, and I say, “How do we usually make an ether?” That name helps them recall the reaction, and then it simplifies to designing the right SN2 step in the synthesis.

  2. Adam Azman
    March 8, 2016 at 4:09 pm #

    Maybe it’s because I ‘name’ the reaction post hoc, rather than AS the introduction to the reaction. I’ll try naming it first next time to see if that’s better 🙂

    Thanks for the advice!

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