Topic 17 - Organic Chemistry II Flashcards
(154 cards)
1
Q
What type of isomerism does optical isomerism fall under?
A
Stereoisomerism (same structural formula, but different arrangement of atoms in space)
2
Q
What are optical isomers?
A
Mirror images of each other
3
Q
What is a chiral carbon?
A
A carbon atom that has 4 different groups attached to it.
4
Q
What is the name for the two optical isomers that can be formed around a choral carbon?
A
Enantiomers
5
Q
What are enantiomers?
A
- Optical isomers that are mirror images of each other that can’t be superimposed.
- They occur when a carbon atom has 4 different groups attached to it.
6
Q
How can you draw the optical isomers of a molecule given to you?
A
1) Locate any chiral centres
• Look for any carbon atoms with 4 different groups attached
2) Draw the isomers
• Draw one enantiomer in a tetrahedral shape
• Draw a mirror image beside it by reflecting it in an imaginary mirror
7
Q
When drawing optical isomers, what do you do when there is more than one chiral centre?
A
Mirror each chiral centre one by one to get all the possible isomers.
8
Q
What properties do optical isomers show?
A
They rotate plane-polarised light.
9
Q
What is the name for the ability of optical isomers to rotate plane-polarised light?
A
They are said to be optically active.
10
Q
What can be said about the optical activity of enantiomers?
A
They rotate plane-polarised light in opposite directions (1 clockwise, 1 anticlockwise)
11
Q
What is the name for a mixture containing equal quantities of each enantiomer of a chiral compound?
A
Racemic mixture
12
Q
What can be said about the optical activity if racemic mixtures?
A
They don’t rotate plane polarised light, because the two enantiomers cancel each other’s light-rotating effect.
13
Q
When you react two achiral compounds to give a chiral product, what can be said about the enantiomer produced?
A
- They will be in equal amounts, so the mixture will be racemic
- This is because the new group(s) have an equal chance of forming each enantiomer
14
Q
Remember to revise the optical activity of the reaction between butane and chlorine.
A
Pg 194 of revision guide.
15
Q
When a single enantiomer reacts to produce a racemic mixture, what does this tell you about the reaction mechanism?
A
It is SN1.
16
Q
When a single enantiomer reacts to produce a single enantiomer product, what does this tell you about the reaction mechanism?
A
It is SN2.
17
Q
When an enantiomer reacts by an SN1 reaction, describe the optical activity of the product. Why?
A
• The mixture is racemic
This is because:
• In step 1, a planar ion is formed
• In step 2, the nucleophile from two sides, which results in two enantiomers
(See diagram pg 195 of revision guide)
18
Q
When an enantiomer reacts by an SN2 reaction, describe the optical activity of the product. Why?
A
• Only one enantiomer is produced
This is because:
• The nucleophile always attacks the molecule from the opposite side to the leaving group
• So only one enantiomer is produced
19
Q
Remember to practise working out the mechanism of a reaction by the optical activity of the products.
A
Pg 195 of revision guide
20
Q
What type of compound are aldehydes and ketones?
A
Carbonyl
21
Q
What are carbonyl compounds?
A
Those containing the C=O functional group.
22
Q
Where do aldehydes have the carbonyl group?
A
At the very end of the carbon chain.
23
Q
Where do ketones have the carbonyl group?
A
In the middle of the carbon chain.
24
Q
How can you tell which carbon the C=O group is on a ketone?
A
There is a number in the name before the “-one”.
25
Do aldehydes and ketones hydrogen bond with themselves? Why?
No, because they don’t have a polar O-H bond.
26
What intermolecular forces do aldehydes and ketones exert on themselves?
* London forces
| * Permanent dipole - permanent dipole interactions
27
How does the boiling point of aldehydes and ketones compare to their equivalent alcohols?
* Aldehydes and ketones have a lower boiling point than alcohols
* Because alcohols can form hydrogen bonds with themselves, while aldehydes and ketones cannot
28
Can aldehydes and ketones form hydrogen bonds with water? Why?
Yes, because:
• Aldehydes and ketones have a lone pair of electrons on the O of the C=O group
• This can be used to form hydrogen bonds with the water molecules
(See diagram on pg 196 of revision guide)
29
Can aldehydes and ketones dissolve in water? Why?
Small aldehydes and ketones:
• Yes
• Because they can form hydrogen bonds with the water
Large aldehydes and ketones:
• No
• Because the intermolecular forces (London forces) between the aldehyde or ketones molecules, and the hydrogen bonding between water molecules, are stronger than the hydrogen bonds that could form between the aldehyde/ketone and the water
30
How does the solubility of aldehydes and ketones change as their size increases?
The larger the aldehyde/ketone, the lower the solubility.
31
What principle do tests to differentiate between aldehydes and ketones work on?
* Aldehydes can be easily oxidised to a carboxylic acid, but a ketone can’t.
* When the aldehyde is oxidised, another compound is reduced
* This reduces compound changes colour and this is detected
32
What are the 3 ways of testing for aldehydes (as oppose to a ketone)?
* Tollens’ reagent
* Fehling’s solution or Benedict’s solution
* Acidified dichromate(VI) ions
33
What is Tollens’ reagent?
* A colourless solution of silver nitrate dissolved in aqueous ammonia
* Ag(NH₃)₂⁺
34
Describe how to prepare Tollens’ reagent.
* Get some silver(I) nitrate solution
* Add a drop of sodium hydroxide solution (to give a precipitate of silver(I) oxide)
* Add just enough dilute ammonia solution to redissolve the precipitate
35
What is the positive result for Tollens’ reagent?
A silver mirror forms on the colourless solution.
36
How is Tollens’ reagent used?
* Colourless solution of silver nitrate dissolved in ammonia is added to the sample
* It is then heated gently in a water bath
* If an aldehyde is present, a silver mirror forms
37
Describe in words how Tollens’ reagent works.
If an aldehyde is present, it will be oxidised, while the Ag(NH₃)₂⁺ is reduced to give solid silver.
38
What is the half-equation for Tollens’ reagent being reduced?
Ag(NH₃)₂⁺(aq) + e⁻ -> Ag(s) + 2NH₃(aq)
39
What is the full equation for a Tollens’ reagent test?
2Ag(NH₃)₂⁺(aq) + RCHO(aq) + 3OH⁻(aq) -> Ag(s) + RCOO⁻(aq) + 4NH₃(aq) + 2H₂O(l)
40
What is Fehling’s solution and Benedict’s solution?
* Fehling’s solution -> Blue solution of complexes copper(II) ions dissolved in silver hydroxide
* Benedict’s solution -> Blue solution of complexes copper(II) ions dissolved in sodium carbonate
41
What is the positive result in the Fehling’s solution or Benedict’s solution test?
A brick-red precipitate appears in the blue solution.
42
Describe in words how Benedict’s/Fehling’s solution works.
If an aldehyde is present, it will be oxidised, while the Cu²⁺ is reduced to give Cu⁺ in Cu₂O, which is a brick-red solid.
43
What is the half-equation for Fehling’s/Benedict’s solution being reduced?
Cu²⁺(aq) + e⁻ -> Cu⁺(s)
44
What is the full equation for a Fehling’s/Benedict’s solution test?
RCHO(aq) + 2Cu²⁺ + 5OH⁻ -> RCOO⁻(aq) + Cu₂O(s) + 3H₂O(l)
45
In a Fehling’s/Benedict’s solution test, what is the brick-red precipitate?
Copper(I) oxide
46
How is Fehling’s solution or Benedict’s solution used?
* Fehling’s/Benedict’s solution is added to the sample
* It is heated
* If an aldehyde is present, a brick-red precipitate is formed
47
What is the formula for dichromate(VI) ions?
Cr₂O₇²⁻
48
When using dichromate(VI) ions to test for an aldehyde, what is it important to remember?
It must be acidified.
49
What is the positive result when using acidified dichromate(VI) ions to test for an aldehyde?
The solution turns from orange to green.
50
Describe in words how acidified dichromate(VI) ions work when testing for an aldehyde.
If an aldehyde is present, it will be oxidised, while the orange Cr₂O₇²⁻ is reduced to give Cr³⁺ in Cu₂O, which is green.
51
What is the half-equation for acidified dichromate(VI) ions being reduced?
Cr₂O₇²⁻ + 14H⁺ + 6e⁻ -> 2 Cr³⁺ + 7H₂O
52
What is the symbol for a reducing agent?
[H]
53
What are aldehydes reduced to?
Primary alcohol
54
What are ketones reduced to?
Secondary alcohol
55
Give the general equation for an aldehyde being reduced.
R-COH + 2[H] -> R-CH₂OH
56
Give the general equation for a ketone being reduced.
R-CO-R¹ + 2[H] -> R-CHOH-R
57
What reducing agent is used to reduce aldehydes/ketones?
LiAlH₄ (Lithium aluminium hydride) in dry ether
58
What type and mechanism of reaction is the reduction of an aldehyde or ketone? Why?
* Nucleophilic addition
| * The reducing agent supplies an H⁻ that acts as a nucleophile and attacks the positive carbon
59
What is a hydroxynitrile?
A molecule with a CN and OH group.
60
Remember to practise drawing out the general structure of a hydroxynitrile.
Pg 198 of revision guide
61
How can a hydroxynitrile be produced from an aldehyde or ketone?
* HCN
* KCN + H⁺
(NOTE: Check these with teacher!)
62
When preparing a hydroxynitrile from an aldehyde or ketone in a lab, what is the preferred method and why?
KCN and H⁺, because HCN is a highly toxic gas.
63
What happens to HCN in water?
It is a weak acid so it dissociates into H⁺ and CN⁻.
64
What type of reaction is the production of a hydroxynitrile from an aldehyde or ketone?
Describe the mechanism.
Nucleophilic addition
STEP 1:
• Arrow from lone pair on CN⁻ to the positive carbon in the aldehyde/ketone
• Arrow from the C=O bond to the O
STEP 2:
• Arrow from that O to the H⁺ floating freely
• Hydroxynitrile is produced
(See diagram pg 198 of revision guide)
65
Is the mechanism for the conversion from aldehyde/ketone to hydroxynitrile more like SN1 or SN2?
SN2 -> The carbonyl is attacked in the first step
66
Describe how the optical activity of the hydroxynitrile produced from an aldehyde/ketone is evidence for the reaction mechanism.
* The mixture produced is racemic and optically inactive.
* This means that the aldehyde/ketone must be attacked from two different sides by the nucleophile (like an SN2) reaction.
* This happens because the atoms around the carbonyl carbon are planar.
(See diagram pg 198 of revision guide)
67
What does 2,4-DNP stand for?
2,4-dinitrophenylhydrazine
68
What does 2,4-DNP test for?
Carbonyl groups (i.e. aldehydes and ketones, not carboxylic acids!)
69
Does 2,4-DNP test for carboxylic acids?
No, only aldehydes and ketones.
70
What is the positive result in a 2,4-DNP test?
Bright orange precipitate
71
Describe how the 2,4-DNP test is carried out.
* 2,4-DNP is dissolved in methanol and concentrated sulfuric acid
* Sample is added
* If an aldehyde or ketone is present, a bright orange precipitate forms
72
How can 2,4-DNP be used to work out the type of aldehyde or ketone present?
* The bright orange precipitate is purified by recrystallisation.
* It is then melted.
* The melting point can be used to identify the original aldehyde or ketone.
73
What type of carbonyl compounds can react with iodine?
* Those with a methyl carbonyl group
| * RCOCH₃
74
Describe the conditions under which a carbonyl compound will react with iodine.
* The carbonyl compound must contain a methyl carbonyl group (RCOCH₃)
* This must happen in the presence of an alkali
75
Remember to practise drawing out a methyl carbonyl group.
Pg 199 of revision guide
76
What carbonyl compounds contain a methyl carbonyl group (and can therefore react with iodine in the presence of an alkali)?
* Ethanal
| * Ketones with at least one methyl group
77
What organic products are made when a carbonyl compound (with -COCH₃) reacts with iodine in the presence of alkali?
* Carboxylic acid
| * Triiodomethane (CHI₃)
78
What is the change observed when a carbonyl compound (with -COCH₃) react with iodine in the presence of alkali?
* Yellow precipitate (of CHI₃)
| * Antiseptic smell
79
What colour and smell of triiodomethane?
* Yellow
| * Antiseptic
80
What is the general equation for a carbonyl compound (with -COCH₃) reacting with iodine in the presence of alkali?
RCOCH₃ + 3I₂ + 4OH⁻ -> RCOO⁻ + CHI₃ + 3I⁻ + 3H₂O
81
What are the different tests involved with carbonyl compound, what do they test for, and what are the positive results?
```
1) Tollens’ reagent
• Tests for aldehydes only
• Goes from colourless to silver mirror
2) Fehling’s/Benedict’s solution
• Tests for aldehydes only
• Goes from blue solution to red precipitate
3) Acidified dichromate(VI) ions
• Tests for aldehydes only
• Goes from orange to green solution
4) 2,4-DNP
• Tests for carbonyl groups (C=O)
• Produces bright orange precipitate
5) Iodine (in alkali)
• Tests for RCOCH₃
• Produces yellow precipitate with antiseptic smell
```
82
What is the functional group for carboxylic acids?
-COOH
83
How can you name a carboxylic acid?
Find and name the longest alkane chain containing the -COOH group, take off the “e” and add “-oic acid”.
84
Where in a molecule will a carboxyl group be found?
Always at the end.
85
How does numbering in a carboxylic acid work?
The carbon in COOH is carbon-1.
86
What happens to carboxylic acids in water?
They dissociate into carboxylate ions and H⁺ ions.
87
Explain the boiling point of carboxylic acids.
* It is very high
| * Because the molecules can form hydrogen bonds with each other
88
Are carboxylic acids soluble in water? Why?
Small carboxylic acids:
• Yes
• Because they can form hydrogen bonds with the water
Large carboxylic acids:
• No
• Because the intermolecular forces between the carboxylic acid molecules, and the hydrogen bonding between water molecules, are stronger than the hydrogen bonds that could form between the carboxylic acid and the water
• The hydrocarbon chains can’t form hydrogen bonds with water but disrupt the hydrogen bonds between the water molecules
89
Remember to practice drawing out how carboxylic acids can form hydrogen bonds with each other and with water.
See diagram pg 200 of revision guide
90
What is the name for the complex formed between two carboxylic acids?
Dimer
91
What are dimers and what do they do?
* When a molecule hydrogen bonds with just one other molecule
* This effectively increases the size of the molecule, increasing the intermolecular forces, and so the boiling point
92
What are the two ways of making a carboxylic acid?
* Oxidation of primary alcohols and aldehydes
| * Hydrolysis of nitriles
93
Describe how a carboxylic acid can be made from a primary alcohol or aldehyde.
Use acidified potassium dichromate(VI) and reflux with the primary alcohol or aldehyde.
94
What are the byproduct when producing a carboxylic acid from a primary alcohol?
When the aldehyde intermediate is made, H₂O is also produced.
95
Describe how a carboxylic acid can be made from a nitrile.
* Reflux the nitrile with HCl
| * Distill off the carboxylic acid
96
When producing a carboxylic acid from a nitrile, how is the carboxylic acid from the mixture?
Distillation
97
Give the general chemical equation for the production of a carboxylic acid from a nitrile.
R-CN + 2H₂O + HCl -> R-COOH + NH₄Cl
98
When a carboxylic acid is produced from a nitrile, what is the byproduct?
NH₄Cl
99
Carboxylic acid + Alkali ->
Carboxylic acid + Alkali -> Salt + Water
100
What type of salt do carboxylic acids form? How are they named?
* Carboxylates
| * They end with “-oate”
101
Carboxylic acid + Carbonate ->
Carboxylic acid + Carbonate -> Salt + Carbon dioxide + Water
102
Carboxylic acid + Hydrogencarbonate ->
Carboxylic acid + Hydrogencarbonate -> Salt + Carbon dioxide + Water
103
CH₃COOH + NaOH ->
CH₃COOH + NaOH -> CH₃COONa + H₂O
104
2CH₃COOH + Na₂CO₃ ->
2CH₃COOH + Na₂CO₃ -> 2CH₃COONa + H₂O + CO₂
105
CH₃COOH + NaHCO ->
CH₃COOH + NaHCO -> CH₃COONa + H₂O + CO₂
106
How can you make an alcohol from a carboxylic acid?
LiAlH₄ in dry ether
107
Can you make an aldehyde from a carboxylic acid?
No, the reducing agent (LiAlH₄) is too powerful, so it is reduced straight to an alcohol.
108
How can you make an acyl chloride from a carboxylic acid?
Add phosphorus pentachloride (PCl₅).
109
Give the equation for the production of an acyl chloride from a carboxylic acid.
R-COOH + PCl₅ -> R-COCl + POCl₃ + HCl
110
What is the functional group of esters?
-COO-
111
What are the two parts of the name of an ester?
1) Alcohol (e.g. propyl)
| 2) Carboxylic acid (e.g. ethanoate)
112
Describe how to name an ester.
1) Look at the alkyl group that came from the alcohol (this is the bit that has no C=O bond). This is the first bit of the name (e.g. propyl)
2) Look at the part from the carboxylic acid (this is the bit with the C=O bond). Swap the “-oic acid” in its name for “-oate”. This is the second part of the name (e.g. ethanoate)
3) Put the two parts together (e.g. propyl ethanoate)
113
What is the suffix for an ester containing a benzene ring in the carboxylic acid part?
Benzoate
114
Name the ester formed from methanol reacting with benzoic acid.
Methyl benzoate
115
When naming an ester, what happens if the carboxylic acid part has a branched chain in it?
Add the attached groups to the second part of the name, with the C=O carbon being carbon-1.
(e.g. X 3-ethylbutanoate)
116
When naming an ester, what happens if the alcohol part has a branched chain in it?
Add the attached groups to the first part of the name, with the carbon neatest to the C-O-C being carbon-1.
(e.g. 2-ethylpropyl X)
117
Remember to practise naming esters.
Pg 202 of revision guide
118
What are the two ways of making an ester?
* Alcohol + Carboxylic acid
| * Alcohol + Acyl chloride
119
Describe how an ester can be produced from an alcohol and carboxylic acid.
* Heat the alcohol and carboxylic acid in the presence of an acid catalyst.
* Distill off the product formed at just below 80°C.
* React with sodium carbonate to react with any carboxylic acid remaining.
* The ester forms a layer on top of the aqueous layer and can be easily separated using a separating funnel.
120
What is esterification?
The reaction between a carboxylic acid and alcohol in the presence of an acid catalyst, in order to produce an ester.
121
When producing an ester from a carboxylic acid and alcohol, what is the byproduct?
Water
122
What type of reaction is esterification?
Condensation
123
Where does the oxygen in the C-O-C bond in an ester come from?
The alcohol.
124
When producing an ester, how is it separated from the mixture?
* Distilling off at just below 80°C
| * It is then purified and separated using a filter funnel (the ester is the top layer)
125
When producing an ester, what is added to the impure product and why?
* Sodium carbonate
| * This is to react with any carboxylic acid remaining
126
Describe the reaction used to produce ethyl ethanoate.
Refluxing ethanoic acid with ethanol and conc. H₂SO₄ as a catalyst
127
What is ethyl ethanoate used for?
* Solvent in chromatography
| * Pineapple flavouring
128
How can an ester be split up?
Refluxing with a dilute acid or alkali
129
What is the type of reaction used to break up an ester?
Hydrolysis
130
What are the two types of hydrolysis of esters?
* Acid hydrolysis
| * Bass hydrolysis
131
What is produced when a dilute acid is refluxed with an ester?
Carboxylic acid and alcohol
132
What is the general equation for acid hydrolysis of esters?
Ester + Water —H⁺, Reflux—> Carboxylic acid + Ethanol
| Note: This is reversible!
133
When hydrolysing an ester, why must a dilute acid be used?
The reaction is reversible, so to get maximum yield and push the equilibrium over to the right, you need to use lots of water.
134
What is produced when a dilute alkali is refluxed with an ester?
Carboxylate ion and alcohol
135
What is the general equation for base hydrolysis of esters?
Ester + OH⁻ -> Carboxylate ion + Ethanol
136
What is a carboxylate ion?
A carboxylic acid with the H missing from the OH.
137
What is the difference between acid and base hydrolysis of esters?
* Acid hydrolysis produces a carboxylic acid and alcohol, while base hydrolysis produces a carboxylate ion and alcohol
* Acid hydrolysis is reversible, while base hydrolysis is not
138
What molecules join to produce a polyester?
* Diols
| * Dicarboxylic acids
139
What are the bonds in a polyester called?
Ester links
140
Describe the structure of an ester link.
-CO-O-
141
Remember to practise drawing out the formation of polyesters.
Pg 203 of revision guide
142
What is the functional group of an acyl chloride?
COCl
143
What is the general formula for an acyl chloride?
CnH(2n-1)OCl
144
What do acyl chloride names end in?
-oyl chloride
145
How are acyl chlorides named?
* Carbon atoms are numbered from the end with the acyl functional group -> Prefixes are added using this
* The name ends in -oyl chloride
146
Remember to practise naming acyl chlorides.
Pg 204 of revision guide
147
As a general rule, how do acyl chlorides react?
By having something substituted for the Cl.
148
What 4 things can acyl chlorides react with?
* Water
* Alcohols
* Concentrated ammonia
* Amines
149
How can a carboxylic acid be produced from an acyl chloride?
Reacting it with cold water.
150
How can an ester be produced from an acyl chloride?
Reacting it with an alcohol at RTP.
151
How can an amide be produced from an acyl chloride?
Reacting it with concentrated NH₃ at RTP.
152
How can an N-substituted amide be produced from an acyl chloride?
Reacting it with an amine at RTP.
153
What is the byproduct of action chloride reactions with anything?
HCl fumes
154
Remember to practise drawing out the equations for acyl chloride reactions.
Pg 204 of revision guide
