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Chemistry · Glossary

What is α,β-Unsaturated carbonyl compounds?

Also known as: alpha,beta-unsaturated carbonyl compound

Definition 26.1 University Chemistry — Year 2 · Chapter 26 — Conjugated Carbonyls: Michael and Robinson

An α,β\alpha,\beta-unsaturated carbonyl compound has a C=C\ce{C=C} double bond between the α\alpha and β\beta carbons of a carbonyl compound, conjugated with the C=O\ce{C=O}: an enone (ketone), an enal (aldehyde), an unsaturated ester or nitrile. The simplest are propenal CHX2=CHCHO\ce{CH2=CHCHO} and but-3-en-2-one CHX2=CHCOCHX3\ce{CH2=CHCOCH3} (methyl vinyl ketone).

Propenal. Top: its three resonance structures; the last two put a positive charge on the carbonyl carbon and on the carbon. Bottom: the Hückel model of (_ O = +, _ CO =; a model). The largest positive charge is on the carbonyl carbon (+0.33, against +0.23 on the carbon); the largest LUMO coefficient is on the carbon (0.66, against -0.58). Propenal. Top: its three resonance structures; the last two put a positive charge on the carbonyl carbon and on the carbon. Bottom: the Hückel model of (_ O = +, _ CO =; a model). The largest positive charge is on the carbonyl carbon (+0.33, against +0.23 on the carbon); the largest LUMO coefficient is on the carbon (0.66, against -0.58). Propenal. Top: its three resonance structures; the last two put a positive charge on the carbonyl carbon and on the carbon. Bottom: the Hückel model of (_ O = +, _ CO =; a model). The largest positive charge is on the carbonyl carbon (+0.33, against +0.23 on the carbon); the largest LUMO coefficient is on the carbon (0.66, against -0.58).
Propenal. Top: its three resonance structures; the last two put a positive charge on the carbonyl carbon and on the β\beta carbon. Bottom: the Hückel model of Chapter 17 (αO=α+β\alpha_{\ce{O}} = \alpha + \beta, βCO=β\beta_{\ce{CO}} = \beta; a model). The largest positive charge is on the carbonyl carbon (+0.33, against +0.23 on the β\beta carbon); the largest LUMO coefficient is on the β\beta carbon (0.66, against −0.58-0.58).
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