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Ch. 22 - Condensations and Alpha Substitutions of Carbonyl Compounds
Wade - Organic Chemistry 9th Edition
Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook
Chapter 22, Problem 3f

Give the important resonance forms for the possible enolate ions of the following:
(f)

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1
Identify the alpha hydrogens in the molecule. Alpha hydrogens are the hydrogens attached to the carbon atoms adjacent to the carbonyl group. In this case, the molecule is a ketone, and the alpha hydrogens are present on the carbons adjacent to the carbonyl carbon.
Determine the possible enolate ions that can form. Deprotonation of an alpha hydrogen by a base leads to the formation of an enolate ion. The enolate ion consists of a negatively charged oxygen atom and a double bond between the alpha carbon and the carbonyl carbon.
Draw the resonance forms of the enolate ion. The negative charge on the oxygen can delocalize to the alpha carbon, forming a resonance structure where the double bond shifts between the alpha carbon and the carbonyl carbon. Use curved arrows to show the movement of electrons.
Consider the stability of the resonance forms. Resonance structures that place the negative charge on the more electronegative atom (oxygen) are generally more stable. However, both resonance forms contribute to the overall stability of the enolate ion.
Repeat the process for all possible alpha carbons in the molecule. In this case, there are two alpha carbons (one on each side of the carbonyl group), so you will need to draw resonance forms for enolate ions formed from deprotonation at each alpha carbon.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Enolate Ions

Enolate ions are reactive intermediates formed from the deprotonation of a carbonyl compound, typically a ketone or aldehyde. They contain a negatively charged carbon atom adjacent to a carbonyl group, which allows for resonance stabilization. This resonance can lead to different structural forms, influencing the reactivity and stability of the enolate in various reactions.
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Resonance Structures

Resonance structures are different Lewis structures for the same molecule that depict the delocalization of electrons. In the case of enolate ions, resonance allows the negative charge to be shared between the carbon atom and the oxygen atom of the carbonyl group. This delocalization stabilizes the enolate ion and is crucial for understanding its reactivity in organic reactions.
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Carbonyl Compounds

Carbonyl compounds, characterized by the presence of a carbon-oxygen double bond (C=O), include aldehydes, ketones, and carboxylic acids. They are key players in organic chemistry due to their electrophilic nature, which allows them to participate in various reactions, including nucleophilic addition and enolate formation. Understanding their structure and reactivity is essential for analyzing enolate ions and their resonance forms.
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