6.1.2 Carbonyls Flashcards
What are carbonyl compounds?
Carbonyl compounds contain a C=O bond and can be classified as either aldehydes or ketones
How do you identify an aldehyde from it’s structure?
In an aldehyde, the C=O group is at the end of the chain, attached to at least 1 hydrogen atom, ends in “-al”
How do you identify a ketone from it’s structure?
In a ketone, C=O group is in the middle of the carbon chain, with no attached hydrogen and the name ends in “-one”
Why are smaller carbonyl compounds soluble in water?
Why are larger carbonyl compounds not soluble in water?
Smaller carbonyls like propanone and ethanal can form hydrogen bonds with water
As the non-polar hydrocarbon part disrupts hydrogen bonding with water so solubility decreases with size
Why do carbonyls have permanent dipole forces?
The C=O bond is polar, allowing dipole-dipole interactions.
Describe the oxidation reaction for primary alcohols?
Primary alcohols are oxidised to aldehydes and then to carboxylic acids
How does Tollen’s reagent test for aldehyde?
Tollen’s reagent oxidises aldehydes to carboxylic acids, reducing silver ions to metallic silver creating a “silver mirror”
What is a reaction of 2,4-dinitrophenylhydrazine with carbonyl compounds?
2,4 DNP reacts with both aldehydes and ketones to form an orange precipitate, which can be used to detect carbonyl groups
How can the melting point of a 2,4-DNP derivative help in identifying a carbonyl compound?
The melting point of the orange crystals formed from 2,4 - DNP can be compared with known values to identify the specific carbonyl compound
How do you distinguish between an aldehyde and a ketone using chemical tests?
Use Tollens reagent
Aldehydes give a silver mirror
ketones don’t react
What reagents are used to reduce carbonyl compounds to alcohols?
NaBH4 or LiAlH4
What is the nueclophilic acidition reaction of carbonyls?
reduction suing NaBh4
followed by addition of water
What is the overall reaction equation for the reducion of propanal?
ch3ch3cho + 2(h) -> CH3CH2CH2OH
What is the nucleophillic addition reaction of propanone?
CH3COCH3 + 2[H] -> CH3CHOHCH3
What type of alcohols are produced from the reduction of aldehydes and ketones?
Aldehydes are produced to primary alcohols, while ketones are reduced to secondary alcohols
How does HCN- react with carbonyl compounds like aldehydes and ketones
HCN- reacts with carbonyl compounds
in a nucleophilic addition reaction
The CN- attacks the carbon
in the C=O bind
breaking the double bond
A H+ attaches to the oxygen = forms OH
hydroxynitrile forms final product
this has OH group and CN group attatched
What conditions are required for the reaction of hydrogen cyanide addition to a carbonyl compound?
Sodium cyanide (NaCN)
Sulfuric Acid (H2SO4)
RTP
What reaction occurs for the reaction of hydrogen cyanide to carbonyl compounds?
undergoes nucleophilic addition
to form hydroxynitrile
What is the characteristic test for the presence of a carbonyl group in an organic compound?
use of 2,4 DNP to detect the presence of a carbonyl group by forming an orange precipitate
How could a technician work out whether a bottle of acid contains pentan-2-one or pentan-3-one?
1) Purify 2,4 - DNP derivative by re-crystallisation
2) Measure the melting point
3) Compare to data values to find a match
Describe how the technician could confirm that the compound is a ketone?
1) Adding 2,4-DNP
- an orange precipitate is formed
- confirms carbonyl
2) Add acidified K2Cr2O7
- no orange to green colour change so not an aldehyde, therefore ketone
3) Adding Tollen’s reagent
- Aldehyde - silver mirror
- Ketone - no reaction so no silver mirror
What type of reaction is Tollen’s reagent being added to an Aldehyde?
Redox
What is a nucelophile?
Electron pair donor
How do you make Tollens reagent?
Add Silver Nitrate and Ammonia
Describe an oxidation and reduction reaction of CH3COCHO that can be carried out during metabolism?
Oxidation Reaction
- Add Tollen’s reagent
- Silver mirror formed
- CH3COCHO+ [O] -> CH3COCOOH
Reduction Reaction
- React with NaBH4
- CH3COCHO+ 4[H] -> CH3CHOHCH2OH
Why was the alcohol heated under reflux rather than distilled?
To ensure alcohol was fully oxidised to the carboxylic acid
Prevents formation of aldehyde
What is the bonding in the carbonyl group?
- 3 sigma bonds around the carbon
- p orbial on carbon and oxygen
- p orbitals overlap creating the pi bond above and below the plane of C-O bond
