Organic Chemistry Chapter 8: Aldehydes & Ketones

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Questions and Answers

What is the primary purpose of hydride addition in the context of carbonyl compounds?

To remove a carbonyl group from a molecule

To oxidize alcohols into carbonyls

To enhance the acidity of aldehydes

To convert C=O to CH-OH (correct)

What characterizes compounds that differ only by the position of a moveable proton?

They are referred to as diastereomers.

They are known as tautomers. (correct)

They are classified as radicals.

They are called enantiomers.

Which of the following statements about enols is correct?

Enols can act as reaction intermediates. (correct)

Enols are always more stable than their keto forms.

Enols do not participate in hydrogen bonding.

Enols can be easily isolated in pure form.

Why is the acidity of a hydrogen atom increased when flanked by two carbonyl groups?

Because of resonance stabilization of the resulting enolate. Signup and view all the answers

What is the main product of the aldol reaction when acetaldehyde reacts with itself in basic solution?

A b-hydroxy aldehyde Signup and view all the answers

In a mixed aldol reaction, which characteristic of the carbonyl partner increases the likelihood of a successful reaction?

Being unhindered and lacking alpha hydrogens Signup and view all the answers

What is the outcome of the dehydration process in aldol condensation?

Formation of conjugated enones Signup and view all the answers

What type of reaction is the Claisen condensation?

A reaction between an ester and a base to produce a b-keto ester Signup and view all the answers

What is the functional group characteristic of aldehydes and ketones?

Carbonyl group (C=O) Signup and view all the answers

How are aldehydes named in terms of IUPAC nomenclature?

By replacing the terminal –e of the alkane name with –al. Signup and view all the answers

In the functional group priority list, where do aldehydes rank?

Fifth Signup and view all the answers

Which method is used for preparing aldehydes?

Oxidizing primary alcohols using PCC. Signup and view all the answers

What is produced when aldehydes undergo hydration?

Geminal diol Signup and view all the answers

When ketones oxidize, which of the following is a typical result?

Cleavage to yield carboxylic acids. Signup and view all the answers

What is the specific result of the reaction of aldehydes with HCN?

Formation of cyanohydrins. Signup and view all the answers

Which statement describes the addition of H–Y to the carbonyl group?

It produces an unstable adduct that is readily reversible. Signup and view all the answers

How does the parent chain for naming ketones get determined?

Longest carbon chain that contains the ketone group. Signup and view all the answers

Which of the following aldehydes has '5-Chloropentanal' as its proper name?

5-Chloropentanal Signup and view all the answers

Which type of compound is typically harder to oxidize, aldehydes or ketones?

Ketones are harder to oxidize than aldehydes. Signup and view all the answers

What type of intermediate is formed when a nucleophilic addition occurs with a carbonyl compound and HCN?

Tetrahedral intermediate Signup and view all the answers

How are common names for some ketones treated in IUPAC nomenclature?

They retain their unsystematic names. Signup and view all the answers

Which of the following effectively oxidizes aldehydes to carboxylic acids?

CrO3 in aqueous acid Signup and view all the answers

Study Notes

Chapter 8: Aldehydes and Ketones

Aldehydes (RCHO) and ketones (R₂CO) are characterized by the carbonyl functional group (C=O).
These compounds are widely found in nature as intermediates in metabolism and biosynthesis.
Examples include pyridoxal phosphate (PLP) and hydrocortisone.

Functional Group Priority

A list of functional groups, ranked from highest to lowest priority, for determining the parent chain in naming organic compounds.
- Carboxylic acids
- Esters
- Amides
- Nitriles
- Aldehydes
- Ketones
- Alcohols
- Amines
- Alkenes/Alkynes
- Alkanes
- Ethers
- Halides

Naming Aldehydes

Aldehydes are named by replacing the terminal -e of the corresponding alkane name with -al.
The parent chain must contain the -CHO group.
If the -CHO group is attached to a ring, use the suffix carbaldehyde.
Examples of common aldehydes and their systematic names are provided in a table.

Naming Ketones

Replace the terminal -e of the alkane name with -one.
The parent chain is the longest chain containing the ketone group.
Numbering begins at the end nearer the carbonyl carbon.
Some ketones have common names, like acetone.

Preparing Aldehydes and Ketones

Primary alcohols can be oxidized to aldehydes using PCC in dichloromethane.
Alkenes can be oxidized to aldehydes and ketones using ozone.
Esters can be reduced to aldehydes using diisobutylaluminum hydride (DIBAL-H).
A 2º alcohol can be oxidized to a Ketone

Preparing Ketones

A 2º alcohol can be oxidized to a ketone.
Ozonolysis of alkenes can yield ketones if one of the unsaturated carbon atoms is disubstituted.

Oxidation of Aldehydes and Ketones

Aldehydes are oxidized efficiently to carboxylic acids by CrO3 in aqueous acid.
Ketones are oxidized with difficulty using hot, alkaline KMnO4, resulting in the cleavage of the C-C bond next to the carbonyl group to form carboxylic acids. Reaction is practical for symmetrical ketones.

Nucleophilic Addition of H₂O (Hydration)

Aldehydes and ketones react with water to form 1,1-diols (geminal diols).
This reaction is reversible, meaning a gem diol can eliminate water.

Addition of H-Y to C=O

Formation of the product is often readily reversible (unstable alcohol).
Favored when Y is an electronegative element that substitutes with the carbonyl group, such as halogen's.

Nucleophilic Addition of HCN (Cyanohydrin Formation)

Aldehydes and unhindered ketones react with HCN to yield cyanohydrins.
The addition of HCN is reversible and base-catalyzed.
Addition of CN- to C=O yields a tetrahedral intermediate, which gets protonated.

Nucleophilic Addition of Grignard Reagents and Hydride Reagents

Treatment of aldehydes or ketones with Grignard reagents yields an alcohol.
Treatment of aldehydes or ketones with hydride reagents (LiAlH4 and NaBH4) yields an alcohol through reduction reaction.

Keto-Enol Tautomerism

A carbonyl compound with a hydrogen atom on its alpha carbon rapidly equilibrates with its corresponding enol.
Compounds that differ only by the position of a moveable proton are called tautomers.

Enols

The enol tautomer is usually present to a very small extent and can not be isolated.
Since the enol tautomer rapidly forms, it serves as a reaction intermediate.

β-Dicarbonyls

When a hydrogen atom is flanked by two carbonyl groups, its acidity is enhanced.
The negative charge of the enolate delocalizes over both carbonyl groups, increasing its stability.

Carbonyl Condensation: The Aldol Reaction

Aldehydes and ketones react with another molecule, forming a β-hydroxy carbonyl compound.
This product (the aldol) dehydrates to yield conjugated enones in acidic or basic conditions.

Practical Mixed Aldols

Reactions using carbonyl partners without α-hydrogens are more likely to be successful and yield mixed aldol products.

Mixed Aldols with Acidic Carbonyl Compounds

Ethyl acetoacetate forms its enolate ion under less basic conditions.
Aldol condensation reactions involving ethyl acetoacetate generally favor a mixed product.

The Claisen Condensation Reaction

Reacting an ester with one equivalent of a base yields a β-keto ester.

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Description

Explore the intriguing world of aldehydes and ketones in this quiz based on Chapter 8 of Organic Chemistry. Understand their structures, naming conventions, and functional group priorities, as well as their significance in nature and organic synthesis. Test your knowledge on these crucial carbonyl compounds!