3.8&9 The Carbonyl Group Flashcards
What is the carbonyl group?
C=O
General nomenclature of aldehydes and ketones?
Aldehyde - RCHO - ethanal - always on the 1st carbon
Ketone - RCOR - propanone - in the middle of the carbon chain
What are some physical property of the carbonyl compounds?
C=O bond is strongly polar
Therefore permanent dipole dipole forces are present
Leading to relatively high boiling points
Solubility decreases in water as the carbon chain increases
Describe the oxidation reactions of aldehydes and ketones?
Aldehydes are oxidised to carboxylic acids using reflux and acidified potassium dichromate VI
Ketones cannot be oxidised as the c-c is too strong
What are the tests to distinguish between aldehydes and ketones?
Aldehyde heated with Fehlings solution turns brick red
Ketones give no reaction (stay deep blue)
Aldehyde heated with tollens reagent forms a silver mirror on the test tube
The aldehyde is oxidised, silver is reduced
Ketones give no reaction
What mechanism can be used with ketones?
Nucleophilic addition
What is formed when reacting HCN with a ketone?
CN and OH
On the carbon where the double bond O was
What is significant about a nitrile?
In CN the ‘N’ is alway on carbon 1 so it is likely there are side chains when naming
What can form as a result of a reaction with HCN?
A racemate can form
With an aldehyde and an asymmetrical/chiral ketone
When can a racemate not form in the reaction with HCN?
Symmetrical/non-chiral ketones
Describe the first stage of the mechanism of nucleophilic addition between a carbonyl group and HCN?
The first arrow goes from the lone pair on the CN- and attacks the C (with the double bond O)
And the second arrow goes from the middle of the double bond C=O on to the oxygen
Describe the second stage of the mechanism of nucleophilic addition between a carbonyl group and HCN?
Then arrow goes from the lone pair on the oxygen to the H+ ion
The final product is an OH group in replace of the double bond O
And a CN group attached on the same carbon
What happens in nucleophilic addition if dilute HCl is added?
A carboxylic acid forms
What conditions are used for reduction of a ketone?
NaBH4
In methanol or aqueous conditions
Describe the mechanism of nucleophilic addition of a carbonyl?
The first arrow goes from the lone pair on a H- ion to attack the C
The second arrow goes from the middle of the C=O bond to the oxygen
Second stage:
The arrow goes from the lone pair of the O- to a H+ ion
Forming an alcohol
For reduction what can and can’t produce racemates?
Asymmetrical ketones can produce racemates
Symmetrical ketones and aldehydes do not form racemates
What is the functional group of carboxylic acids? Position and naming?
O
||
R-C - O - H
RCOOH
At the end of the carbon chain
Ends in -oic acid
What is significant about the OH group in carboxylic acids?
The OH group in carboxylic acids is more acidic that the OH group in alcohols
What are some physical properties of carboxylic acids?
They form hydrogen bonds with water and themselves (in the solid state)
Methanoic acid to butanoic acid (all 4) are soluble in water
Higher boiling points than alkanes of similar Mr
They have characteristic smells
How can we identify carboxylic acids?
Measure their melting point and comparing them to a table of values of known melting points
We can use a thiele tube or do it electrically
Describe the carboxylic acids losing a proton?
The H+ ion from the OH group is lost leaving a negative carboxylate ion
The negative charge is shared over the whole carboxylate group
This delocalisation makes the ion more stable
How can we distinguish carboxylic acids from alcohols?
Carboxylic acids are weak but strong enough to react with sodium hydrogencarbonate NaHCO3
This releases CO2 (also ester and water produced)
What is the functional group of esters?
O
||
R - C - O - R
RCOOR
With COO in the middle
How do we name esters?
Based on the parent acid
Ethanoic acid -> ethanoates
First part: methyl, ethyl etc.. comes from the chain attached to the O
Second part: methanoate, ethanoate etc… comes from the chain attached to the carbon (includes the carbon in the COO)