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Organic Chemistry by Brown, Iverson, Anslyn, Foote | Mayya's Study Guide | Chapter 16

Chapter 16: Aldehydes and Ketones


Table of Contents:



Structure and Bonding


Nomenclature


Aldehydes:

  1. Find the longest continuous carbon chain that contains the aldehyde and number from the carbon with the aldehyde group

  2. End the name in "al"


Ketones:

  1. Find the longest continuous carbon chain that contains the ketone group and number from the carbon closest to the ketone functional group.

  2. End the name in "one" and specify the number of the carbon to which =O is attached.



Physical Properties

Due to the =O, aldehydes and ketones are polar molecules. The carbon with =O is a Lewis acid (can be attacked) and the O is the lewis base (can attack).


Reaction Themes

Carbonyl reactions can happen in acidic and in basic conditions


Addition of Carbon Nucleophiles


1. Addition of Grignard Reagents


Addition of Grignard Reagents to ketones and aldehydes
Addition of Grignard Reagents to ketones and aldehydes

Mechanism Of Grignard Addition to the Carbonyls


Mechanism Of Grignard Addition to the Carbonyls
Mechanism Of Grignard Addition to the Carbonyls

How to predict the reactants of ketone/aldehyde +RMgBr when product is given?


Mayya's Trick

  1. Break between carbon with OH and its neighboring C

  2. Turn OH into =O and add MgBr (or Li) to the carbon broken off


How to predict the reactants of ketone/aldehyde +RMgBr when product is given?
How to predict the reactants of ketone/aldehyde +RMgBr when product is given?

2. Addition of Anions of Terminal Alkynes


Addition of Anions of Terminal Alkynes to ketones of aldehyde
Addition of Anions of Terminal Alkynes to ketones of aldehyde

Mechanism


Note: Once alkyne is attached, we can do alkyne reactions on it to produce

other groups.


3. Addition of Hydrogen Cyanide


Addition of Hydrogen Cyanide to a ketone or aldehyde
Addition of Hydrogen Cyanide to a ketone or aldehyde


The Wittig Reaction


Witting reaction converts carbonyls (ketones or aldehydes ) into alkenes (C=C).



Preparing Wittig Reagent


Mechanism for preparing Wittig Reagent


Mechanism for preparing Wittig Reagent
Mechanism for preparing Wittig Reagent

Note: If there is a C=O next to the negative charge on the Wittig Reagent, it will be E selective.



How to predict the reactants when Wittig product is given?

Mayya's Trick

  1. Break between the two carbons that have the double bond

  2. To the most substituted carbon attach =O. To the less substituted carbon attach PPh3. Put negative charge on the carbon with PPh3 and positive charge on P



Addition of Oxygen Nucleophiles


Hemiacetal is a molecule with a carbon that is attached to an OH and an OR group.

An acetal is molecule with a carbon attached to two OR groups.


Formation of hemiacetal under basic conditions

Formation of hemiacetal under basic conditions
Formation of hemiacetal under basic conditions

Mechanism


Acetal Formation****(very important)

Mechanism of Acetal Formation

This mechanism may seem a little lengthy. Here is what helps me think about it and do it correctly.

I do the mechanism with the knowledge of what the product should be. The group that needs to leave will be protonated until it becomes a good leaving group. Groups that need to stay will be deprotonated.


Mechanism of Acetal Formation
Mechanism of Acetal Formation

Acetals are very useful in serving as protecting groups for ketones and aldehydes.


Protecting of Alcohols as Acetals



Addition of Nitrogen Nucleophiles


Formation of an Imine from an Aldehyde or a Ketone

Note: this reaction uses primary amine. Primary amine has a nitrogen attached to one alkyl group only.

Formation of an Imine from an Aldehyde or a Ketone
Formation of an Imine from an Aldehyde or a Ketone

Mechanism for formation of an Imine from an Aldehyde or a Ketone

Mechanism for formation of an Imine from an Aldehyde or a Ketone
Mechanism for formation of an Imine from an Aldehyde or a Ketone

How to predict the reactants that gave the following amine?

Mayya's Trick

  1. Break between the carbon and nitrogen

  2. Attach =O to the carbon. Attach H to the nitrogen broken off.




Reaction of Aldehyde/Ketone with secondary amine to form an enamine




Keto-Enol Tautomerism


Alpha hydrogens are hydrogens on a carbon next to the C=O group. Alpha hydrogens are acidic. When you take an alpha hydrogen off, the conjugate base is resonance stabilized.


Keto-Enol Tautomers In Acid And Base
Keto-Enol Tautomers In Acid And Base

Oxidation

Oxidation of Aldehydes




Reduction

Multiple reagents can be used to reduce ketones and aldehydes to alcohols.



Reductive Amination


Reductive Amination
Reductive Amination


Reduction of a Carbonyl Group to a Methylene Group


Reduction of a Carbonyl Group to a Methylene Group
Reduction of a Carbonyl Group to a Methylene Group

Complete the following reactions.



Wolff Kishner Mechanism


Wolff Kishner Mechanism
Wolff Kishner Mechanism

Reactions at an α-Carbon


Racemization


Racemization
Racemization

If the alpha carbon has a specific stereochemistry, it will lose its stereochemistry once it becomes an enol (have a double bond). When it equilibrates back to the keto form, it can have both R or S stereochemistry.


Deuterium Exchange


Alpha Halogenation in Acid

Alpha Halogenation in acid
Alpha Halogenation in acid


Mechanism for Alpha Halogenation in acid
Mechanism for Alpha Halogenation in acid

Alpha Halogenation in Base

Alpha Halogenation in Base
Alpha Halogenation in Base


Mechanism for Alpha Halogenation in base
Mechanism for Alpha Halogenation in base


Mayya's Reaction Study Guide chapter 16
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