Carbonyl Compounds

Front 1

Two types of carbon compounds

Back 1

- aldehyde

-ketone

Front 2

Aldehyde contain ____ R groups

Back 2

1

Front 3

Ketones contain ____ R groups

Back 3

2

Front 4

Aldehyde

Back 4

Front 5

Ketone

Back 5

Front 6

Test for Carbonyls

Back 6

- Brady's reagent (2,4- dinitrophenylhydrazine)

-deep orange precipitate formed in the presence of a carbonyl compound

Front 7

Tests to distinguish between aldehydes and ketones

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- Tollen's Reagent

- Fehling's Reagent

- acidified potassium dichromate/ potassium manganate

Front 8

Tollen's Reagent [Ag(NH3)2]+

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- when warmed with tollen's Reagent aldehydes are oxidized to carboxylic acids

- the silver complex ions are reduced to silver atoms

- silver mirror is seen on the side of the test tube

- ketones do not reacts with tollens' reagent as they cannot be oxidized to carboxylic acids

Front 9

How is Fehling's solution made

Back 9

- by mixing Fehling's A (which contains Cu2+ (aq) ions) and Fehling's B (contains a complexing reagent and an alkali)

Front 10

Reaction with Fehling's solution

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- when warmed with Fehling's solution, aldehydes are oxidized to carboxylic acids.

- the blue Cu2+ ions changes to an orange red precipitate of copper (I) oxide

-Cu2+ ions oxidize the aldehyde and are themselves reduced to the copper (I) state

- ketones cannot be oxidized to carboxylic acids

Front 11

Reactions with acidified potassium manganate or potassium dichromate

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- this reaction is done under reflux with excess oxidizing agent

-aldehydes are oxidized to carboxylic acids

- the purple potassium manganate decolourizes and turns brownish (MnO4-(purple) -------> Mn2+(very pale pink) / MnO2 (brown)

- in the case of potassium dichromate, the solution changes from orange to green. ( Cr2O72-(orange) -----> Cr3+(green) )

- ketones are not oxidized

Front 12

Nucleophilic addition reactions with carbonyl compounds

Back 12

.....

Front 13

The C=O bond in aldehydes and ketones are polarized due to the electronegative oxygen atom

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....

Front 14

Nucleophiles which attack carbonyls

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- CN- and HSO4-

Front 15

Overall reaction

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- partially positive C atom in C=O bond is attacked by a nucleophile

- nucleophile forms a bond with C atom

- negatively charged intermediate formed ( negative charge found on O atom )

- H+ ion from acid/water in the reaction mixture bonds to the O atom

Hint 15

Example

Front 16

Aldehydes are reduced to

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Primary alcohols

Front 17

Ketones are reduced to

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Secondary alcohols

Front 18

Reduction of aldehyde and ketones

Back 18

This is also a nucleophilic addition. H-H from reducing agent adds across the =

Front 19

Reducing agent for reduction of aldehydes and ketones

Back 19

Lithium aluminum hydride (LiAlH4)