ALDEHYDES AND KETONES

What is an aldehyde?

• the C=O is at the end of the chain

• name will end in -al

What is a carbonyl?

contains a C=O bond

What is a ketone?

• the C=O is in the middle of the chain

• name will end in -one

What’re the intermolecular forces found in carbonyls?

pure carbonyls cannot hydrogen bond to themselves but are attracted by permanent dipole forces

How soluble are carbonyls?

smaller carbonyls are soluble in water as they can form hydrogen bonds with water

How can carbonyls react?

the C=O bond is polarised as O is more electronegative than the carbon, so the positive carbon atom will attract nucleophiles

What can primary alcohols be oxidised into?

aldehydes and ketones

What can secondary alcohols be oxidised into?

ketones

What can tertiary alcohols be oxidised into?

do not oxidise

What is the reagent used to oxidise alcohols?

potassium dichromate

What occurs in the oxidation of aldehydes?

• forms a carboxylic acid

• reagent - potassium dichromate and dilute sulfuric acid

• conditions - heat under reflux

How can you test for aldehydes using tollens reagent?

• heat gently with tollens

• with aldehydes a silver mirror coats the test tube

• with ketones there is no visible change

How can you test for aldehydes using fehlings solution?

• heat gently

• with aldehydes the blue ions turn red

• with ketones there is no visible change

What reducing agents are used to reduce carbonyls into alcohols?

• NaBH4

• LiAlH

What conditions is required to reduce carbonyls?

• NaBH4 in aqueous ethanol

• room temperature and pressure

What’re aldehydes reduced into?

primary alcohols

What’re ketones reduced into?

secondary alcohols

Outline the nucleophilic addition mechanism for propanone

What is catalytic hydrogenation?

• carbonyls are reduced using catalytic hydrogenation

• reagent - hydrogen and nickel catalyst

• conditions - high pressure

What happens when hydrogen cyanide is added to carbonyles?

• forms hydroxynitrile

• reagent - potassium cyanide and dilute sulfuric acid

• conditions - room temperature and pressure

What is the nucleophilic addition mechanism between propanone and :CN-?

Why does nucleophilic addition of HCN to aldehydes and ketones form a racemate?

the planar carbonyl group is approached equally from both sides of the HCN attacking species