Chapter 26 - Carbonyls Flashcards
(92 cards)
1
Q
What functional group do aldehydes and ketones have ?
A
C=O
2
Q
Where is the functional group found in aldehydes ?
A
- Found at the end of a carbon chain.
- The carbon atom is attached to one or two hydrogen atoms
3
Q
What is the functional group written as in aldehydes ?
A
CHO
4
Q
What is the simplest aldehyde ?
A
Methanal AKA formaldehyde
5
Q
Where is methanal commonly used ?
A
Used in solution to preserve biological specimens
6
Q
Where is the functional group found in ketones ?
A
- Found in a carbon chain
- The functional groups is joined to two carbon atoms in the carbon chain
7
Q
What is the functional group written as in ketones ?
A
CO
8
Q
What is the simplest ketone ?
A
Propanone
9
Q
Where is propanone commonly used ?
A
- Industrial solvent
- Nail varnish remover
10
Q
How can aldehydes be oxidised to carboxylic acids ?
A
Refluxed with acidified potassium dichromate and dilute sulphuric acid
11
Q
Do ketones undergo oxidation reactions ?
A
- No they do not
- The lack of reactivity provides chemists with a way of distinguishing between aldehydes and ketones
12
Q
What is the difference between a C=C bond in alkenes and the C=O bond in carbonyl compounds ?
A
- The C=C bond in alkenes is non polar
- The C=O bond in carbonyl compounds is polar
13
Q
What is more electronegative in the C=O bond ?
A
- The oxygen is more electronegative than the carbon
- This makes the carbon end of the bond slightly positive and the oxygen end slightly negative
14
Q
Due to the polarity of the C=O bond, what do the aldehydes and ketones react with ?
A
Nucleophiles
15
Q
What type of mechanisms used for carbonyl compounds ?
A
Nucleophilic addition
16
Q
What is NaBH4 used for ?
A
It is used as a reducing agent to reduce aldehydes and ketones to alcohols
17
Q
How is an aldehyde/ketone reduced into an alcohol ?
A
They are usually warmed with NaBH4 in aqueous solution
18
Q
What is hydrogen cyanide (HCN) ?
A
- Liquid
- Colourless
- Extremely poisonous at room temperature
19
Q
What does the reaction of a carbonyl compound with HCN allow to happen ?
A
It allows the length of the carbon chain to increase
20
Q
What does the reaction between an aldehyde and hydrogen cyanide make ?
A
A hydroxynitrile
21
Q
What is 2,4-DNP used for ?
A
It is used to detect the presence of the carbonyl functional group in both aldehydes and ketones
22
Q
What is 2,4-DNP also known as ?
A
- 2,4-dinitrophenylhydrazine
- Brady’s reagent
23
Q
What do you expect to form when you add 2,4-DNP in the presence of the carbonyl group ?
A
- A yellow or orange precipitate
- Called a 2,4-dinitrophenylhydrazone
24
Q
In practical work how is 2,4-DNP used ?
A
Dissolved in methanol and sulphuric acid
- pale orange solution
25
What are the dangers of using 2,4-DNP ?
It can be very hazardous because friction or a sudden blow can cause it to explode
26
How can we distinguish between an aldehyde and a ketone ?
Add Tollen’s reagent
27
What is Tollen’s reagent ?
A solution of silver nitrate in aqueous ammonia
28
In the presence of an aldehyde group, what does the addition of Tollen’s reagent cause to form ?
A silver mirror is produced
29
What ions does Tollen’s reagent contain ?
Ag+ (aq)
30
What do the Ag+ ions act as ?
They act as an oxidising agent in the presence of ammonia
31
What gets reduced when testing with Tollen’s reagent ?
Silver ions are reduced to silver
32
What gets oxidised when testing with Tollen’s reagent ?
The aldehyde is oxidised to a carboxylic acid
33
What is a carboxylic acid ?
A carboxylic acid is an organic acid which contains the carboxyl functional group
34
What does the carboxyl group contain ?
It contains both a carbonyl group and a hydroxyl group
35
Where can you find carboxylic acids ?
- In medicines
- Fruit juices
- Vinegar
- Rhubarb leaves
36
What are carboxylic acids used for ?
They are used in organic synthesis as starting materials or intermediates in the formation of more useful compounds
37
Give an example of a carboxylic acid derivative
- Aspirin
- It can be synthesised from salicylic acid
38
What is the solubility of carboxylic acids like ?
Carboxylic acids with up to four carbon atoms are soluble in water
39
Which bonds in a carboxylic acid are polar ?
- C=O
- O-H
40
What do the polar bonds in a carboxylic acid allow to happen ?
They allow the carboxylic acid to form hydrogen bonds with water molecules
41
Trend in solubility for a carboxylic acid as the chain gets bigger
As the number of carbon atoms increases, the solubility decreases as the non polar carbon chain has a greater effect on the overall polarity of the molecule
42
What kind of acids are carboxylic acids ?
- They are weak acids
- They only partially dissociate in water
43
General equation for the dissociation of a carboxylic acid
HCOOH →← H+ + HCOO-
44
What kind of reactions do carboxylic acids take place in ?
- Redox reactions with metals
- Neutralisation reactions with bases
Bases include alkalis, metal oxides and carbonates
45
What is formed in the reactions of carboxylic acids ?
Carboxylate salts
46
What is the carboxylate ion ?
- It is an ion in the salt
- It is named by changing the -ic acid to -ate
47
What kind of a reaction is a carboxylic acid reacting with a metal ?
A redox reaction
48
What is formed when a carboxylic acid reacts with a metal ?
Hydrogen gas and the carboxylate salt
49
What would you observe when a carboxylic acid reacts with a metal ?
The metal disappearing and effervescence as hydrogen is formed
50
What type of a reaction is the reaction of a carboxylic acid with a base ?
A neutralisation reaction
51
What can be classified as a base ?
- Metal oxides
- Alkalis
- Carbonates
52
What is formed when a carboxylic acid reacts with a metal oxide ?
Salt and water
53
What is formed when a carboxylic acid reacts with an alkali ?
Salt and water
54
What would you observe when a carboxylic acid reacts with an alkali ?
You may not see a reaction as the two solutions react together to form the salt in an aqueous solution
- Nothing visible is formed
55
What is formed when a carboxylic acid reacts with a carbonate ?
Carbon dioxide gas, water and salt
56
What would you observe when a carboxylic acid reacts with a carbonate ?
If the carboxylic acid is in excess a solid carbonate would disappear
57
How can you check for the carboxyl group ?
- React it with sodium carbonate
- If it reacts with sodium carbonate it has a carboxyl group
- If it does not, then it is likely to be a phenol as phenols are not acidic enough to react with carbonates
58
What is a derivative of a carboxylic acid ?
A compound that can be hydrolysed to form the parent carboxylic acid
59
What is the common sequence of carboxylic acids ?
- They all have an acyl group
- R-C=O
60
What are the derivatives of carboxylic acids ?
- Ester
- Acyl chloride
- Acid anydride
- Amide
61
How do you name an ester ?
- Remove the -oic acid suffix and replace it with -oate
- The alkyl chain attached to the oxygen atom of the COO group is then added as the first word in the name
62
How do you name an acyl chloride ?
Remove the -oic acid suffix from the parent carboxylic and replace it with -oyl chloride
63
How is an acid anhydride formed ?
It is formed by the removal of water from two carboxylic acid molecules
64
What is esterification ?
The reaction of an alcohol with a carboxylic acid to form an ester
65
What are the conditions of esterification ?
The alcohol is warmed with a carboxylic acid with a small amount of concentrated H2SO4
66
What is the catalyst in esterification ?
Concentrated H2SO4
67
What is hydrolysis ?
The chemical breakdown of a compound in the presence of water or in aqueous solution
68
How can esters be hydrolysed ?
By aqueous acid or alkali
69
What is acid hydrolysis ?
The reverse of esterification
70
What has to occur for acid hydrolysis to occur ?
- The ester is heated under reflux with dilute aqueous acid
- The ester is broken down by water, with the acid acting as a catalyst
71
What are the products of acid hydrolysis ?
- Carboxylic acid
- Alcohol
72
What is alkaline hydrolysis known as ?
Saponification
73
Is alkaline hydrolysis reversible ?
No it is irreversible
74
What are the conditions for saponification ?
Ester is heated under reflux with any compound that has OH- ions
75
What are the products of saponification ?
- Carboxylate ion
- Alcohol
76
How can acyl chlorides be prepared ?
They can be prepared directly from the parent carboxylic acid by reaction with thionyl chloride (SOCl2)
77
Why is the reaction to form acyl chlorides carried out in a fume cupboard ?
This is because the products formed in the reaction, SO2 and HCl, are toxic
78
What is the reactivity of acyl chlorides like ?
They are very reactive
79
Why are acyl chlorides useful in organic synthesis ?
They can easily be converted into carboxylic acid derivatives with good yields
80
How do acyl chlorides react ?
They react with nucleophiles by losing the chloride ion whilst retaining the C=O bond
81
What does the reaction between an acyl chloride and an alcohol form ?
They react together to form esters
82
Can carboxylic acids react with esters to form phenols ?
No, they are not reactive enough
83
What can react with a phenol to create a phenyl esters ?
- Acyl chlorides
- Acid anhydrides
84
What happens when water is added to an acyl chloride ?
A violent reaction takes place
Forms dense and steamy hydrogen chloride
85
What is formed when water is added to an acyl chloride ? (Hydrolysis)
- Carboxylic acid
- Hydrogen chloride
86
What can ammonia and amines act as ?
Nucleophiles
87
How do ammonia and amines act as nucleophiles ?
They donate their lone pair of electrons to an electron deficient species
88
What is formed when ammonia/amines react with acyl chlorides ?
Amides
89
What is a primary amide ?
- Formed when ammonia reacts with an acyl chloride
- The nitrogen atom is attached to one carbon atom
90
What is formed when a primary amine reacts with an acyl chloride ?
A secondary amide
91
What is a secondary amide ?
The nitrogen is attached to 2 carbon atoms
92
What is the reactivity of acid anhydrides like ?
They are less reactive than acyl chlorides
