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)
What are some properties of esters?
Short chain esters are fairly volatile
They have pleasant smells used in flavourings and perfumes
Also used as solvents and plasticisers
Fats and oils are esters with longer carbon chains
How is an ester formed?
Esterification (condensation reaction)
Carboxylic acid + alcohol ⇌ ester + water
Using a strong acidic catalyst (H2SO4 or HCl)
Describe the hydrolysis of esters?
Ester + water ⇌ carboxylic acid + alcohol
Using a strong acidic catalyst (H2SO4)
Requires heat
If done at room temp needs really strong catalyst
(Tends to produce an equilibrium mixture containing an ester, water, acid and alcohol
Describe saponification?
A triglyceride (ester) is hydrolysed by boiling with 3NaOH
Into
Glycerol and 3 sodium salts NaCOOR
The Na salts are ionic and dissociate to form Na+ and RCOO-
RCOO has to ends: non-polar hydrocarbon chain and the polar, ionic COO- group
Hydrocarbon mixes with grease, COO- mixes with water (acts as a cleaning agent)
Uses for esters?
Solvent
Plasticiser
Flavourings
Perfumes
What is biodiesel?
A renewable fuel made from oils (rape seed oil)
Rape seed oil is a triglyceride ester
How is biodiesel made?
A triglyceride + 3CH3OH (methanol) with a strong alkali catalyst (KOH)
Forming glycerol +
CH3-COO-R
CH3-COO-R1
CH3-COO-R2
(R’s relate to the fatty acid chains on the triglyceride)
What is glycerols IUPAC name? Also?
Propane - 1,2,3 - triol
E IN PROPANE!!!!
Forms hydrogen bonds = soluble in water
Functional group and naming of acyl chlorides?
O
||
R - C - Cl
RCOCl
Ethanoyl Chloride - CH3COCl
The C in the COO counts in the carbon chain
What does an acid anhydride look like?
RCOOOCR
Can look like a zig zag on it’s side
Could just be a straight chain
What are the reactions we need to know?
RCOCl and (RCO)2O with
H20
ROH
2NH3
2RNH2
What are the RCOCl reactions?
Acyl Chloride - RCOCl with
Water -> carboxylic acid + HCl
Alcohol (ROH) -> ester + HCl
Excess ammonia (2NH3) -> amide (RCONH2) + NH4Cl
Excess primary amide (2RNH2) -> substituted amide (RCONHR) + RN^+H3Cl^-
What is the test for an acyl chloride?
Add H2O
Misty white fumes of HCl
What are the (RCO)2O reactions?
Acid anhydride - (RCO)2O with
Water -> 2 carboxylic acids
Alcohol (ROH) -> ester + carboxylic acid
Excess ammonia (2NH3) -> amide (RCONH2) + RCOO^-NH4^+
Excess primary amide (2RNH2) -> substituted amide (RCONHR) + RCOO^-N^+H3R
What are the advantages of using acid anhydrides over acyl chlorides?
Cheaper
Less corrosive
Doesn’t react with water as readily
Safer: the bi-product is ethanoic acid rather than HCl
What is significant about the production of aspirin?
Ethanoyl anhydride is used as a reagent due to the bi-product being ethanoic acid (not HCl)
Describe the mechanism for RCOCl and H2O?
Arrow from O lone pair on water to C
Arrow from middle of C=O onto the oxygen
Arrow from O- lone pair to middle of C-O bond at the top
Arrow from middle of C-Cl onto the Cl
Arrow from middle of H-O onto the O+
Forms RCOOH + HCl
Describe the mechanism for RCOCl and ROH?
Arrow from O lone pair on water to C
Arrow from middle of C=O onto the oxygen
Arrow from O- lone pair to middle of C-O bond at the top
Arrow from middle of C-Cl onto the Cl
Arrow from middle of H-O onto the O+
Forms RCOOR + HCl
Describe the mechanism for RCOCl and 2NH3?
Arrow from N lone pair on NH3 to C
Arrow from middle of C=O onto the oxygen
Arrow from O- lone pair to middle of C-O bond at the top
Arrow from middle of C-Cl onto the Cl
Arrow from middle of H-N onto the N+
Arrow from another NH3 (lone pair on N) onto the H (same H as previous step)
Forms RCONH2 + NH4Cl
Describe the mechanism for RCOCl and 2RNH2?
Arrow from N lone pair on RNH2 to C
Arrow from middle of C=O onto the oxygen
Arrow from O- lone pair to middle of C-O bond at the top
Arrow from middle of C-Cl onto the Cl
Arrow from middle of H-N onto the N+
Arrow from another RNH2 (lone pair on N) onto the H (same H as previous step)
Forms RCONHR + RNH3Cl
What mechanism is used in the acyl chloride reactions?
Nucleophilic addition elimination
