Module 6 Chapter 26
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What is the carbonyl functional group
A group with a carbon double bonded to an oxygen
What is a feature of the carbon oxygen double bonded
Due to electronegativity of O it is a polar bond
What are the two simplest examples of carbonyls and what are their relative functional groups
Aldehydes - DRAW IT Ketones - DRAW IT
What are features of aldehydes
Where the carbonyl is bonded to at least one hydrogen Suffix al Carbon is the carbonyl group
What are features of ketones
Carbonyl bonded to two carbons Suffix ‘one’ Carbon 1 is the closest to the carbonyl
How are carbonyl compounds formed
As a result of the oxidation of alcohols —> where acidified dichromate ions are used as the oxidising agent
What are the oxidation reactions that primary alcohols undergo
Partial oxidation (distillation) forms aldehydes (CHO) Complete oxidation (reflux) forms carboxylic acids (COOH)
What are the oxidation reactions that secondary alcohols undergo
OH is attached to carbon with 2 carbon chains and 1 H atom Complete oxidation (reflux) forms ketone
What can aldehydes be oxidised to and what are the reagents and colour changes
They will be oxidised by acidified potassium dichromate —> forming carboxylic acids The orange Cr2O7 2- ions are reduced forming green Cr3+
What are features of the oxidation reactions that ketones can undergo
As ketones are difficult to oxidise, so will not undergo the same oxidation reactions therefore there is no colour change.
Therefore how can you identify the difference between an aldehyde or ketone
As when heated under reflux with acidified potassium dichromate, it will remain orange if it is a ketone and will turn green if it is an aldehyde.
What causes the reactivity of aldehydes and ketones
The nature of the C=O bond As the C=O bond has both pi bonding and sigma bonding It is polar
What occurs due to the polarity of the C=O bond
Aldehydes and ketones can take part nucleophilic attack where a nucleophile attacks a partially positive C resulting in addition across C=O
What can aldehydes and ketones be reduced to and what is required
Their respective alcohols with a reducing agent
What is the reagent when ketones and aldehydes are reduced
Warm sodium tetrahydroborate (III) solution (NaBH4)
What is the reaction when ethanal is reduced to ethanol
CH3CHO + 2[H] —> CH3CH2OH
What are and ketones aldehydes reduced to
Aldehyde —> Primary alcohol Ketones —> Secondary alchol
What is required for the nucleophilic addition of aldehydes and ketones
NaBH4 which releases a hydride ion (H-) that act as nucleophiles and attack the electron deficient carbon atom in the C=O bond
What does the H- ion do in nucleophilic addition
Donating a pair of electrons making a dative bond At the same time the pi bond of the carbonyl breaks
Draw the mechanism for the nucleophilic addition of propanal with NaBH4
DRAW IT
What happens after the intermediate anion forms in nucleophilic addition
The intermediate anion that forms donates a pair of electrons to a hydrogen on a water molecule, creating a bond, whilst at the same time the O-H bonds breaks.
What can the anion also donate electrons to apart from water molecules
The anion can also donate electrons to a H+ ion from an acid
What are the products of the nucleophilic substitution with NaBH4
The respective alcohol and a hydroxide ion
What can cyanide act as
A nucleophile and reduce carbonyl groups so the compound contains: . A hydroxyl (-OH) group . A nitrile groups (-C triple bond N)