6.1.2 - Carbonyls

Question 1

Describe the solubility of aldehydes and ketones

Answer 1

• soluble in H2O
• because they form hydrogen bonds with H2O via lone pair on O and 𝜹+ region on H

Question 2

Name the type of intermolecular forces between aldehydes and ketones

Answer 2

london forces

Question 3

Name the type of reaction: aldehyde/ketone -> alcohol

Answer 3

nucleophilic addition, NaBH4 provides H:- nucleophile

Question 4

Name the product of nucleophilic addition with :CN- nucleophile: alkene + NaCN

Answer 4

produces a hydroxynitrile

Question 5

Describe the test for a carbonyl

Answer 5

add 2,4-DNP
positive: red/orange/yellow precipitate formed

Question 6

How can 2,4-DNP be used to find melting points of carbonyls?

Answer 6

• above test and result
• purify solid by recrystallisation
• compare melting point of pure crystals formed with melting points of all common aldehydes and ketones

Question 7

Describe the test to distinguish between aldehydes and ketones

Answer 7

• add Tollen’s reagent
• aldehyde: silver mirror
• ketones: colourless

Question 8

What is the C=O bond made up of? Is it polar?

Answer 8

𝝅-bond and sigma bond
polar so can react with nucleophiles

Question 9

Describe the mechanism for the reaction of carbonyl with NaBH4

Answer 9

• :H- LP attracted and donated to 𝜹+ C in C=O bond, forming a dative covalent bond between H- and C
• 𝝅 bond in C=O breaks by heterolytic fission, forming - charged intermediate
• O donates LP to H in water molecule
• intermediate protonated to form an alcohol

Question 10

Describe the mechanism for the reaction of carbonyl with NaCN/H+

Answer 10

• :CN- LP attracted and donated to 𝜹+ C in C=O, forming dative covalent bond
• 𝝅 bond in C=O breaks by heterolytic fission, forming a - charged intermediate
• intermediate protonated by donating LP to a H ion

Question 11

Define heterolytic fission

Answer 11

one bonded atom receives both electrons
breaking of covalent bond