3.8 Aldehydes and ketones

Question 1

What is the carbonyl group

Answer 1

C=O

Question 2

What is the functional group and general formula for an aldehyde

Answer 2

RCHO (C double bonded to O, single bond to H and R)
end

Question 3

What is the functional group for a ketone

Answer 3

RCOR’ (C double bonded to O)
middle

Question 4

How do you name aldehydes

Answer 4

-al suffix (C=O on the end of a chain)

Question 5

How do you name ketones

Answer 5

-one suffix (designate number for which carbon C=O is on)

Question 6

What kind of imfs do molecules with the carbonyl group have? Why

Answer 6

Permanent dipole-dipole due to polar C=O bond (O is delta negative)

Question 7

How soluble are they in water? What influences solubility

Answer 7

Yes - form hydrogen bonds between water molecules and oxygen of C=O
As C chain length increases, solubility decreases

Question 8

Which bond in carbonyl compounds is usually involved in reactions, why

Answer 8

C=O due to the polarity of the bond
Large difference in electronegativity between C and O

Question 9

What is the strongest bond in carbonyl compounds

Answer 9

C=O

Question 10

Draw a mechanism for the nucleophilic addition of HCN to a carbonyl compound

Answer 10

Google

Question 11

Why is the addition of HCN important

Answer 11

Increases the length of the carbon chain by one carbon atom - very useful

Question 12

Will the product of HCN added to a carbonyl compound have optical isomers, why

Answer 12

Yes
In the aldehyde/ketone the carbonyl carbon is planar, so the :CN- can attack from either above or below, forming enantionmers

Question 13

What is the name of the product when HCN is added to a carbonyl compound

Answer 13

Hydroxynitriles (OH and CN groups)

Question 14

What happens when an aldehyde is added to Fehling’s solution

Answer 14

Reduced to CU+ ions –> colour change to brick red ppt

Question 15

What happens when a ketone is added to Fehling’s solution

Answer 15

Stays blue

Question 16

What happens when an aldehyde is added to Tollen’s reagent

Answer 16

Silver mirror forms as Ag+ reduced to Ag(s)

Question 17

What happens when a ketone is added to Tollen’s reagent

Answer 17

No visible change

Question 18

What is another oxidising agent for alcohols and aldehydes? What is the colour change

Answer 18

Acidified potassium dichromate (VI) - H2SO4 and K2Cr2O7
Colour change from orange to green

Question 19

What is a reducing agent for aldehydes and ketones
What ions does this release in solution

Answer 19

NaBH4 (sodium tetrahydridoborate (III), releases an H- ion

Question 20

Write an equation for the reduction of pentan-2-one and for 3-methylbutanal

Answer 20

CH3COCH2CH2CH3 + 2[H] -> CH3CH(OH)CH2Ch2CH3
CH3CH2CH2(CH3)CHO + 2[H] -> CH3CH2CH2(CH3)CH2OH

Question 20

Draw and name a mechanism for the reduction of an aldehyde

Answer 20

Nucleophilic addition
Google