AC8: Carbonyls Flashcards
What is the carbonyl group
C=O
What are the other functional groups that carbonyl refers to
-Aldehydes
- Ketones
What is the short hand way of writing aldehyde
-CHO
What do aldehyde compounds name end in
-al
What is the short hand way of writing ketone group
-CO
What do ketone compounds name end in
-one
What is the colour change of the dichromate ions when reduced
- Orange to green
What 2 bonds make up the C=O carbonyl group
- Sigma bond
- Pi bond
What is the main difference between the C=C double bond and the C=O double bond
The C=O double bond is polar because oxygen is much more electronegative than carbon
Are carbonyl groups reactive or unreactive with electrophiles
Unreactive
Why do nucelophiles attack the carbonyl group C=O
Since the carbon is slightly positive due to the dipole
Why are aldhehydes and ketones polar
Because of the higher electronegativity of the oxygen, compared to the carbon
Why are the boiling points for carbonyl compounds higher than alkanes and alkenes of similar size
Since the dipoles in carbonyl C=O allows permanent dipole-dipole interactions between molecules which are stronger than London forces
Why do carbonyl compounds have lower boiling points than carboxylic acids and alcohols of similar size
Since carbonyls cannot form hydrogen bonds since there is no H bonded to the oxygen
Why are short chain aldehydes and ketones soluble
Since the oxygen in the C=O can form hydrogen bonds with other compounds such as water
What is the chemical equation for the reduction of ethanal to ethanol
CH3CHO + 2[H] -> CH3CH2OH
What type of reaction is the reaction with NaBH4 and aldehydes and ketones
Reduction reaction
What is the name of the mechanism when NaBH4 reacts with an aldehydes or a ketone
Nucleophilic addition
What is the nucleophile in the compound NaBH4
H- (hydride ion)
Draw the mechanism for the reaction between ethanal and aqueous, acidified sodium cyanide solution
Look in the year 2 notes for answer page 54
Draw the mechanism for the reaction between ethanal and NaBH4
Look in the year 2 notes for answer page 54
Describe the 4 steps in the nucleophilic addition reaction with NaBH4
- The lone pair of electrons from the hydride ion is attracted and donated to the slightly positive carbon atom in the aldehyde or ketone C=O double bond
- A dative covalent bond is formed between the hydride ion and the carbon atom of the C=O double bond
- The Pi bond in the C=O double bond breaks by heterolytic fission forming a negatively charged intermediate
- The oxygen atom of the intermediate donates a lone pair of electrons to a hydrogen atom in a water molecule. The intermediate has then been protonated to form an alcohol
How do we get the CN- ion
From NaCN and an acid
Why cannot we just use the HCN
Because it’s a lethally toxic gas
How do you get alkene to carbonyl
Alkene - alcohol - carbonyl
How do you get haloalkane to carbonyl
Haloalkane- alcohol - carbonyl
How do you get alcohol to hydroxynitrile
Alcohol - carbonyl - hydroxynitrile
How do you get a hydroxynitrile from a carbonyl
Add NaCN and an acid
What is added to test for a carbonyl , both aldehyde and ketone
2,4- dinitrophenylhydrazine / 2,4 - DNP
What is produced when 2,4 -DNP is added to a carbonyl
An orange / red solid
What can you do with the orange / red solid that is produced after 2,4-DNP is added to a carbonyl
- Recrystallise
- Then measure the melting point
What does measuring the melting point of the recrystallised orange/ red solid formed from reacting 2,4 -DNP with a carbonyl
It identifies what carbonyl when you’re given the values of the melting points
What is the reagent used to test for aldehydes
Tollen’s reagent
What does a positive Tollen’s test produce
A silver mirror
What type of reaction occurs during the Tollens’ test
Redox
In the Tollens’ test what is oxidised and what is reduced
Aldehyde is oxidised
Ag is reduced
What is the only carbonyl that the Tollens’ test works for
Aldehydes
What is Tollens’ reagent
A mix of Ag and NH3
What is the molecular formula of Tollens’ reagent
Ag(NH3)2)
What are the conditions when using the Tollens’ test
Warm
What is needed to convert an aldehyde or a ketone back to an alcohol
NaBH4
State the names of the reagents that would be used to produce hydrogen cyanide in a lab reaction
- Sodium cyanide
- Sulfuric acid
What is the functional group in this molecule : (CH3CH2O)2)
Acid anhydride
Why is the reaction between a carbonyl and a cyanide ion important in organic synthesis
Because it increases the length of carbon chain
