Aldehyde

Mastery of the reactions of aldehydes and ketones, which are crucially important in biochemistry, is probably the largest single challenge of MCAT organic.

The reactions of aldehydes and ketones represent the largest and most challenging set of mechanisms you must master for the new MCAT. These mechanisms are more important than any for helping you unravel biochemical reactions. What can seem inscrutably complex in an enzymatic mechanism often can be reduced to a familiar pattern if you have ready access to the concepts governing aldehyde and ketone reactions. Much of the organic that does appear on the new MCAT will be couched to this kind of exercise. The focus of MCAT organic chemistry is seeing whether you can shine the light of organic reaction chemistry onto the biochemical context.

WikiPremed Resources





Aldehydes & Ketones Mechanisms
Mechanisms and explanations from the Organic Mechanisms Pocketbook

Reactions of Aldehydes and Ketones Images
Image gallery for study with links to larger teaching JPEGs for classroom presentation

Question Drill for Aldehydes and Ketones
Conceptual Vocabulary Self-Test

Basic Terms Crossword Puzzle

Basic Puzzle Solution

Learning Goals

Proficiency 

Be capable of characterizing the two major classes of aldehyde-ketone reactions, those involving nucleophilic attack on the carbonyl carbon and those occuring by means of keto-enol tautomerism.

Although you don't need to worry about every proton movement, you should be able to reproduce the decisive phases of Acetal Formation, Reductive Amination, and Reaction of Aldehydes and Ketones with Grignard Reagents.

Be able to recognize and characterize these other reactions involving nucleophilic attack on a carbonyl carbon if they are presented to you: The Wittig Reaction, The Wolff-Kishner Reaction and The Cannizzaro Reaction.

Recognize an enol. Be comfortable reproducing acid or base catalyzing enolization on paper.

Understand what it means to say that Aldol Condensation involves both keto-enol tautomerism and nucleophilic attack on the carbonyl carbon. Know this reaction backwards and forwards.

Be able to predict the product from the reagents for Alpha Halogenation, Haloform Reaction, as well as Conjugate Nucleophilic Addition. Have a good sense of these mechanisms.

Understand the place of aldehydes and ketones in the redox sequence with alcohols and carboxylic acids.

Suggested Assignments

Review the basic terms for reactions of aldehydes & ketones using the question server. Complete the fundamental terms crossword puzzle. Here is the solution to the puzzle.

Read pp. 79-82 and pp. 95-105 in ExamKrackers Chemistry. Perform practice items 49-56 on pp. 87-88 (practice items for aldehydes & ketones, alcohols, and amines). Perform practice items 57-64 on pp. 104-105.

Review the web resources for reactions of aldehydes & ketones.

Conceptual Vocabulary for Aldehydes and Ketones

Alpha carbon
The alpha carbon in an aldehyde or ketone refers to the first carbon after the carbonyl carbon.
Addition reaction
In an addition reaction two or more molecules combine to form a larger one.
Enol
Enols are alkenes with a hydroxyl group affixed to one of the carbon atoms composing the double bond.
Keto-enol tautomerism
Keto-enol tautomerism refers to a chemical equilibrium between a keto form and an enol.
Aldol
An aldol adduct is a beta-hydroxy ketone or aldehyde resulting from the addition of a ketone enolate to an aldehyde.
Acetalisation
Acetalisation is an organic reaction that involves the formation of an acetal or ketal.
Acetal
An acetal is a molecule with two single bonded oxygens are attached to the same carbon atom which is also bonded to an alkyl or aryl group and a hydrogen.
Protecting group
A protecting group is introduced into a molecule by chemical modification of a functional group in order to obtain chemoselectivity in a subsequent chemical reaction.
Grignard reaction
The Grignard reaction is an organometallic chemical reaction involving alkyl- or aryl-magnesium halides with electrophiles.
Enolate anion
An enolate anion is the anion of an enol, formed by loss of a proton from the alpha carbon of a carbonyl group.
Nucleophilic conjugate addition
Nucleophilic conjugate addition occurs by reaction of a nucleophile at the beta position of alpha-beta unsaturated carbonyl compounds.
Tollens reagent
Tollens' reagent is usually ammoniacal silver nitrate, an oxidizing agent, which is itself reduced to silver metal. It is used as a test for aldehydes.
Ketal
A ketal is a molecule with two single bonded oxygens attached to the same carbon atom which is also bonded to two alkyl or aryl groups.
Schiff base
A Schiff base is a functional group that contains a carbon-nitrogen double bond with the nitrogen atom connected to an aryl or alkyl group, but not hydrogen.
Enone
An enone is an unsaturated chemical compound or functional group consisting of a conjugated system of an alkene and a ketone.
Cyanohydrin reaction
The cyanohydrin reaction is an organic reaction by an aldehyde or ketone with a cyanide anion or a nitrile to form a cyanohydrin.
Wolff-Kishner reduction
The Wolff-Kishner reduction is a chemical reaction that fully reduces an aldehyde or ketone to an alkane.
Enamine
An enamine is an unsaturated compound derived by the reaction of an aldehyde or ketone with a secondary amine followed by loss of a molecule of water.
Haloform reaction
The haloform reaction is a chemical reaction where a haloform is produced by the multiple halogenation of a methyl ketone in the presence of a base.
Alkylimino-de-oxo-bisubstitution
Alkylimino-de-oxo-bisubstitution in organic chemistry is the organic reaction of carbonyl compounds with amines to imines.
Wittig reaction
The Wittig reaction is a chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide to give an alkene and triphenylphosphine oxide.
Thioacetal
Thioacetals are the sulfur analogue of acetals. They are prepared in a similar way to acetals: by reacting a thiol with an aldehyde.
Iodoform reaction
The iodoform test is a qualitative chemical test for the detection of ketones and aldehydes carrying an alpha methyl group in which the reagents are iodine and sodium hydroxide.
Clemmensen reduction
The Clemmensen reduction is a chemical reaction described as a reduction of aldehydes or ketones to alkanes using zinc amalgam and hydrochloric acid.
Advanced terms that may appear in context in MCAT passages
Reductive amination
Reductive amination is a chemical reaction which involves the conversion of a carbonyl group to an amine.
Michael addition
The Michael addition is the nucleophilic addition of an carbanion to an alpha, beta unsaturated carbonyl compound. It is one of tne of the most useful methods for the mild formation of carbon-carbon bonds.
Pinacol coupling reaction
A pinacol coupling reaction is an organic reaction in which a carbon-carbon covalent bond is formed between the carbonyl groups of an aldehyde or a ketone in presence of an electron donor in a free radical process.
Cannizzaro reaction
The Cannizzaro reaction is a chemical reaction that involves the base-induced disproportionation of an aldehyde lacking a hydrogen atom in the alpha position.
Corey-Fuchs reaction
The Corey-Fuchs reaction is a series of chemical reactions designed to transform an aldehyde into an alkyne.
Johnson-Corey-Chaykovsky reaction
The Johnson-Corey-Chaykovsky reaction is a chemical reaction in which a carbonyl is converted to an epoxide by the action of a sulfonium ylide.
Willgerodt rearrangement
The Willgerodt rearrangement is an organic reaction converting an aryl alkyl ketone to the corresponding amide by reaction with ammonium polysulfide.
Stork enamine alkylation
The Stork enamine alkylation involves the addition of an enamine to an alpha,beta-unsaturated carbonyl acceptor in a process similar to the Michael reaction. The product is then hydrolyzed by an aqueous acid to produce a 1,5-dicarbonyl compound.