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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