6.1.2: Carbonyl compounds

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)

Question 3

What is the functional group for a ketone?

Answer 3

RCOR’ (C double bonded to O)

Question 4

How do you name aldehydes?

Answer 4

-al suffix (C=O is 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 intermolecular forces do molecules with

the carbonyl group have? Why?

Answer 6

Permanent dipole-dipole due to the polar C=O

bond (O is ∂-)

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

Why is the addition of HCN important?

Answer 10

Increases the length of the carbon chain by one
carbon atom allowing more useful molecules to
be made.

Question 11

Will the product of HCN added to a carbonyl

compound have optical isomers? Why?

Answer 11

Yes they will. In the aldehyde/ketone, the
carbonyl carbon is planar, so the :CN- can attack
from either above or below, forming two enantiomers.

Question 12

What is the name of the product when HCN is added

to a carbonyl compound?

Answer 12

Hydroxynitriles (have OH and CN groups)

Question 13

What is Fehling’s solution? What colour is it?

Answer 13

Copper complex ions, blue

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

No visible change → stays blue

Question 16

How do you test for a carbonyl compound?

Answer 16

Use Brady’s reagent - 2,4-dinitrophenylhydrazine

If a carbonyl compound is present an orange precipitate is formed

Question 17

What is in Tollens’ reagent?

Answer 17

Silver complex ions in colourless solution.

Question 18

What happens when an aldehyde is added to

Tollen’s reagent?

Answer 18

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

Question 19

What happens when a ketone is added to Tollen’s

reagent?

Answer 19

No visible change

Question 20

What is another oxidising agent for alcohols and aldehydes? What change in colour does this undergo?

Answer 20

Acidified potassium dichromate (VI) - H2SO4 and

K2Cr2O7. Colour change from orange to green.

Question 21

What is a reducing agent for aldehydes and

ketones? What ions does this release in solution?

Answer 21

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

Question 22

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

and for 3-methylbutanal.

Answer 22

CH3COCH2CH2CH3 + 2[H] → CH3CH(OH)CH2CH2CH3

CH3CH2CH2 (CH3)CHO + 2[H] → CH3CH2CH2(CH3)CH2OH

Question 23

How do you convert an aldehyde to form a carboxylic acid?

Answer 23

Oxidation of aldehydes using Cr2O7

2-/H+ (i.e. K2Cr2O7/H2SO4)