Comments on: What’s The Alpha Carbon In Carbonyl Compounds?

By: James Ashenhurst

James Ashenhurst — Mon, 10 Jun 2024 18:57:48 +0000

That’s a valid question. Since one of the ketones is in the enol form, the OH has many properties of a carboxylic acid.

For this reason these compounds are sometimes called ‘vinylogous acids” since they undergo many reactions of carboxylic acids.

For example it’s possible to replace the OH group with Cl and perform addition-elimination reactions, much like one can perform nucleophilic acyl substitution reactions. https://en.wikipedia.org/wiki/Vinylogy

By: Madhav Mittal

Madhav Mittal — Thu, 06 Jun 2024 05:32:46 +0000

MOC QUIZ ID-0407
In the diketo compound, as the most stable tautomer will be 1-keto-2-enol form, so shouldn’t it be consider as alpha-beta unsaturated carbonyl compound?

By: Find out the chemistry behind AHAs and BHAs in skin care - Emotion Master

Find out the chemistry behind AHAs and BHAs in skin care - Emotion Master — Thu, 16 May 2024 15:14:57 +0000

[…] AHA and BHA, “Alpha” and “Beta” designate the positions of the Hydroxy group concerning the Carboxylic Acid group in their chemical […]

By: James Ashenhurst

James Ashenhurst — Thu, 17 Nov 2022 18:29:41 +0000

In reply to Todd.

Of course, alpha beta, and gamma are all relative terms. I thought about changing the diagram to put a blue “alpha” on the position where gamma is written to accomodate this point, but felt it would add some unnecessary clutter.

Furthermore, from a practical perspective with the beta keto ester, it is impossible to get deprotonation at the gamma carbon without deprotonating the alpha carbon first, and even then only after resorting to an extremely strong base to form the di-anion. So in this particular case I’m going to leave it as gamma.

By: James Ashenhurst

James Ashenhurst — Thu, 17 Nov 2022 17:28:15 +0000

In reply to Todd. Good point Todd. Thank you.

By: Todd

Todd — Thu, 17 Nov 2022 15:59:42 +0000

With regard to multiple functional groups, in the beta-keto acid example at the top of the page, I see the carbon labeled gamma as being alpha. It is both (gamma to the ester carboxyl carbon but alpha to to the ketone carbon). However for me, alpha is more relevant as in my biochemistry class, I often point out that our reactions involve the special nature of the alpha carbon (aldol and Claisen condensations, Citrate Synthase, etc…). Being gamma is not as relevant.

By: James Ashenhurst

James Ashenhurst — Thu, 15 Sep 2022 17:03:49 +0000

In reply to Dion.

yes – technically it would be 1,8-addition. The term, “1,8-addition” has even been used: https://pubs.acs.org/doi/10.1021/jo00038a053

By: James Ashenhurst

James Ashenhurst — Thu, 15 Sep 2022 17:01:48 +0000

In reply to Swagnik.

It wouldn’t apply to the first molecule because there’s no carbonyl.
For the second, it’s a relationship issue.
So in CH3C=OCH2CH2CHO, the CH3 is alpha to the C=O; the first CH2 is alpha to the C=O but beta to the CHO; the next CH2 is beta to the C=O but alpha to the CHO.

By: James Ashenhurst

James Ashenhurst — Thu, 31 Mar 2022 18:49:43 +0000

In reply to shailya. Thank you, glad you found it helpful shailya. James

By: shailya

shailya — Thu, 31 Mar 2022 18:21:23 +0000

Marvellous explanation, quite helpful. Especially the problems at the end are quite worthful.