Carbonyls and carboxylic acids

Question 1

Describe aldehydes

Answer 1

• Aldehydes have a carbonyl functional group which is found at the end of a carbon chain. The carbon atom of the carbonyl group is attached to one or two carbon atoms

Question 2

Describe ketones

Answer 2

• In ketones, the carbonyl functional group is attached to two carbon atoms in the carbon chain

Question 3

What suffix do you add to ketones/aldehyde

Answer 3

• ketones = one
• aldehyde = al

Question 4

How do u name aldehydes and ketones

Answer 4

• in aldehydes, the carbon atom is always numbered carbon 1 so therefore al just needs to be added to the prefix of the longest carbon chain
• In ketones, the carbonyl atoms is given the lowest number if it is the highest priority

Question 5

What are aldehydes oxidised to?

Answer 5

• aldehydes can be oxidised to carboxylic acids when refluxed using acidified dichromate ions

Question 6

What is the difference in reactivity of carbonyls

Answer 6

• in alkenes, the c=c bond is non polar whereas in carbonyls the c=o bond is polar as the oxygen is more electronegative than the carbon.
• This causes the electrons to be attracted to the oxygen atom and make the oxygen electronegative and the carbon positive.
  -Due to this, they can attract nucleophiles and undergo nucleophilic addition

Question 7

What is used as a reducing agent for carbonyls

Answer 7

• sodium tetrahydriborate, NaBH4. The aldehyde or ketone is usually warmed with NaBH4, reducing agent in aqueous solution

Question 8

What can aldehydes be reduced to?

Answer 8

• aldehydes are reduced to primary alcohols using NABH4

Question 9

Write an equation for the reduction of butanal

Question 10

What can ketones be reduced to?

Answer 10

• They can be reduced to secondary alcohols by NaBH4

Question 11

Write an equation for the reduction of butan-2-one

Question 12

What is the reaction of carbonyls with HCN

Answer 12

• HCN adds across the c=o bond and increases the carbon chain length, creating a hydroxynitrile
• This is done with sodium cynanide and sulfuric acid as hydrogen cynanide is a dangerous compound thatis poisonous

Question 13

What happens in the mechanism of nucleophilic addition of carbonyls

Answer 13

1. the lone pair on the hydride ion H- is attracted and donates its pair of electrons to the positive carbon atom in the c=o bond
2. A dative covalent bond forms between the hydride ion and the carbon atom
3. The pi bond in the c=o bond breaks by heterolytic fission which forms an negatively charged intermediate
4. The oxygen atom of the intermediate donates a lone pair of electrons to a hydrogen atom of a water molecule
5. The hydrogen then donates these electrons to the oxygen in the water molecule

Question 14

What is the difference in the mechanism of cyanide and hydride ions

Answer 14

• in the mechanism for cyanide, the intermediate is just a hydrogen ion which is supplied by sulfuric acid

Question 15

Draw the two mechanisms.