6.1.2 Carbonyl Compounds Flashcards
What is the carbonyl functional group
C=O
How is an aldehyde different from a ketone
An aldeHyde has the carbonyl on the side (terminal carbon) and the carbon with the double bond to O also has a H attached.
In a ketone the C with the double bond to the O has no H attached (on its own).
What are the main types of carbonyl containing compounds
aldehydes and ketones
Explain the solubility of carbonyls
The carbonyl group is soluble because a lone pair on O can form a hydrogen bond with an H in a water molecule
What type of intermolecular forces exist in carbonyl compounds?
permanent dipole-permanent dipole interactions due to the d+ carbon and d- oxygen.
How can an aldehyde be produced via oxidation?
Heat a primary alcohol with acidified potassium dichromate and distil off the product.
How can a ketone be produced via oxidation?
Heat a secondary alcohol under reflux with acidified potassium dichromate
Write an equation for the oxidation of ethanol to a carbonyl
CH3CH2OH + [O] —> CH3CHO + H2O
Write an equation for the oxidation of ethanal
CH3CHO + [O} –> CH3COOH
Write an equation for the oxidation of propan-2-ol to a carbonyl
CH3CH(OH)CH3 + [O] –> CH3COCH3 + H20
What observation is made when oxidising an alcohol with acidified potassium dichromate and why is this?
orange –> green
The Cr ion in dichromate changes colour as it is reduced from Cr +6 to Cr +3
What conditions are needed for the reduction of carbonyls and carboxylic acids?
Use of sodium borohydride (NaBH4) reducing agent and dilute acid
How does NaBH4 work?
It provides H- nucleophile which attacks the d+ carbon atom.
Write an equation for the reduction of ethanal
CH3CHO + 2{H} –> CH3CH2OH
What type of reaction is reduction with NaBH4?
nucleophilic addition
nucleophile because the hydride ion (H-) is an electron pair donor
Addition because two smaller molecules join to form one larger molecule.
Give the mechanism for the reaction of ethanal with HCN
See notes
What reagents are needed for the reaction of a carbonyl with HCN and why
NaCN and acid
HCN is toxic so NaCN and H+ are needed to generate the HCN in situ
Write an equation for the reaction of ethanal with HCN. Name the product
CH3CHO + HCN –> CH3CH(OH)CN
(NaCN/H2SO4 written over arrow)
Product = 2-hydroxypropanenitrile
What type of reaction is the reaction of a carbonyl with HCN?
nucleophilic addition
nucleophile because the hydride ion (H-) is an electron pair donor
Addition because two smaller molecules join to form one larger molecule.
Why are reactions of carbonyl compounds with HCN useful to organic chemists?
They extend the length of the carbon chain.
How can you identify an organic compound with optical isomers
If a carbon atom in the compound has 4 different groups attached to it.
How can you test for a carbonyl group
Add 2,4-dinitrophenylhydrazine (2,4-DNP) (Brady’s reagent). If a carbonyl group is present then a yellow-orange precipitate will be seen
How can you distinguish an aldehyde and ketone chemically
Warm the compound with Tollen’s reagent. If a silver mirror forms, the compound is an aldehyde. If there is no visible change, then the compound is a ketone
What is Tollen’s reagent?
Ammoniacal silver
How can you distinguish an aldehyde and ketone using a physical method?
Take the precipitate formed with Brady’s reagent and filter and purify it by recrystallisation. Test the melting point and compare with a database.
How does Tollen’s reagent work?
The silver ions in Tollen’s reagent are reduced
Ag+ + e –> Ag
This works with an aldehyde because it can be oxidised. A ketone cannot be oxidised so it can’t act as a reducing agent.
