CPR Organic Carbonyl Chemistry

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Chemical Processes and Reactions - Organic Chemistry - Carbonyl Chemistry

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Carbonyl Containing Functional Groups

Aldehydes

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Ketones

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Esters

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Carboxylic Acids

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Amides

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Acyl Halides

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Acid Anhydrides

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Carbonates, Carbamates, Ureas

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Nucleophilic Addition to C=O

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The pi bond is stronger and the bond is polarised due to O's electronegativity.

The bond is polarised giving these orbitals:

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These are the resonance structures of the carbonyl group:

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Carbonyl Group Electron Movement

When nucleophiles attack the C=O group they do so by passing electrons from their HOMO to the LUMO of the carbonyl.

a) Curly arrow representation

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b) Orbitals involved

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Reversible Additions

The addition of cyanide can be reversed by adding a base because cyanide is a good leaving group.

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The addition of water is also reversible through the formation and collapse of hydrates.

The bigger the rate constant the more hydrate formed.

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Three Factors Influence the Extent of Hydration

1) Steric Hindrance

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2) Electron Withdrawing Groups

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3) Delocalisation

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Addition of Alcohols

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Some hemiacetals are stable because the alcohol attacks in an intramolecular fashion.

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Hemiacetals in Acid

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Hemiacetals in Base

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Irreversible Addition at a Carbonyl

MORE COMMON

Addition of carbon nucleophiles - Grignard's Reagent

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Reagents add to carbonyl - Metal ion acts as a Lewis Acid

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Similar Reagents

Organolithium Reagents are similar:

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Reduction of carbonyl compounds is observed when bulky Grignard's are used.

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Cannizzaro Reaction

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Mechanism:

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Reduction of a Carbonyl is Best Done with NaBH

Ketones are reduced to secondary alcohols

Aldehydes are reduced to tertiary alcohols

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or LiAlH

Reaction mechanism with LiAlH  is more complex and takes place in an inert solvent such as ether (this is because LiAlH  reacts violently with water to give Hydrogen)

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