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)

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 delta -)

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 a carbonyl
compound, using :Nu- to represent
the nucleophile.

Answer 10

check

Question 11

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

Answer 11

check

Question 12

Why is the addition of HCN important?

Answer 12

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

Question 13

Will the product of HCN added to a carbonyl compound have optical isomers? Why?

Answer 13

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 14

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

Answer 14

Hydroxynitriles (have OH and CN groups)

Question 15

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

Answer 15

Copper complex ions, blue

Question 16

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

Answer 16

Reduced to Cu+ ions → colour change to brick red ppt

Question 17

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

Answer 17

No visible change → stays blue

Question 18

What is in Tollens’ reagent?

Answer 18

Silver complex ions, colourless solution

Question 19

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

Answer 19

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

Question 20

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

Answer 20

No visible change

Question 21

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

Answer 21

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

Question 22

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

Answer 22

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

Question 23

Draw and name a mechanism for the reduction of an aldehyde.

Answer 23

nucleophillic addition

and check

Question 24

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

Answer 24

CH3COCH2CH2CH3 + 2[H] → CH3CH(OH)CH2CH2CH3 CH3CH2CH2(CH3)CHO + 2[H] → CH3CH2CH2(CH3)CH2OH