4.8 Further Organic Chemistry Flashcards
(104 cards)
1
Q
What are structural isomers?
A
Chemicals that have the same molecular formula but their atoms are arranged differently.
2
Q
Give four chemicals with the molecular formula C4H10O.
A
Butan-1-ol, betan-2-ol, 2-methylpropan-1-ol, diethyl ether.
3
Q
What are stereoisomers?
A
Chemicals that have the same molecular formula and their atoms arrange in the same way but their bonds are arranged differently in space.
4
Q
Name the two types of stereoisomerism.
A
E/Z isomerism and optical isomerism.
5
Q
Give the conditions for E/Z isomerism to occur.
A
There must be a C=C double bond with two different groups attached to each of the double bonded carbons.
6
Q
How are the higher priority groups arranged in Z (cis) isomers?
A
They’re on the same side.
7
Q
How are the higher priority groups arranged in E (trans) isomers?
A
They’re on opposite sides.
8
Q
What is a chiral carbon?
A
A carbon atom with four different groups attached to it. These groups can be arranged in two different ways around the central carbon.
9
Q
Describe enantiomers (or optical isomers).
A
They are mirror images of each other. They cannot be superimposed.
10
Q
What does optically active mean?
A
Something that rotates plane-polarised light.
11
Q
How does the optical activity of two optical isomers differ?
A
One enantiomer rotates the plane of polarised light clockwise whilst the other rotates it anticlockwise.
12
Q
What is a racemic mixture (racemate)?
A
A racemic mixture contains equal quantities of each enantiomer of an optically active compound.
13
Q
Which mechanism preserves optical activity?
A
Sn2 because the mechanism only has one step. The nucleophile always attacks the opposite side to the leaving group.
14
Q
What is the carbonyl functional group?
A
C=O
15
Q
Name two compound that contain a carbonyl group.
A
Aldehydes and ketones.
16
Q
Where is the carbonyl on an aldehyde?
A
At the end of the carbon chain.
17
Q
Where is the carbonyl on a ketone?
A
In the middle of a carbon chain.
18
Q
What do aldehydes and ketones hydrogen bond with?
A
Water, but not themselves.
19
Q
Why does aldehydes and ketones have a lower boiling temperature than their corresponding alcohols?
A
Alcohols can hydrogen bond with themselves.
20
Q
Which has the lower bounding point, propanal or pronanone?
A
Propanal.
21
Q
Explain why large aldehydes or ketones don’t dissolve in water.
A
As chain length increase, so does intermolecular (London) forces. If the chain is large enough, the intermolecular forces will be stronger than the hydrogen bonds that could form with water, so it will not dissolve.
22
Q
What is the product of a carbonyl compound and hydrogen cyanide?
A
A hydroxynitrile.
23
Q
Describe the mechanism
A
Nucleophilic addition.
24
Q
Give the equation for the dissociation of hydrogen cyanide.
A
HCN ⇋ H+ + CN-
25
Give an alternate reagent for hydrogen cyanide.
Acidified potassium cyanide.
26
Give one precaution you should take when using acidified potassium cyanide.
Carry out any reactions in the fume cupboard.
27
Describe the optical activity of the product of an asymmetrical ketone with CN-.
It's a racemic mixture.
28
Why do aldehydes and CN- always produce racemic mixtures?
Because the C=O group is planar and can be attacked from either side.
29
What does Brady's reagent test for?
A carbonyl group.
30
What is Brady's reagent?
2,4-dinitrophenylhydrazine (2,4-DNPH) dissolved in methanol and conc sulfuric acid.
31
What is the positive result of a 2,4-DNPH test?
A bright orange precipitate (if a carbonyl group is present).
32
How can you identify a carbonyl compound using its precipitate formed from its reaction with Brady's reagent?
Recrystallise it and perform a melting point analysis. Compare the result to a table of known values.
33
How could you purify the product of a carbonyl compound with 2,4-DNPH?
Recrystallisation.
34
Describe how the tests that differentiate aldehydes and ketones work.
Aldehydes can be easily oxidised to a carboxylic acid whilst ketones are not easily oxidised. If a reagent changes colour when it's reduced it will give a positive test for an aldehyde.
35
What is Tollen's reagent?
Silver nitrate dissolved in aqueous ammonia.
36
Describe a positive test for an aldehyde using Tollen's reagent.
A silver mirror forms when it's heated with an aldehyde.
37
Give the half equation to show how a silver mirror is formed.
Ag(NH3)2`+(aq) + e- → Ag(s) + 2NH3(aq).
38
What is Fehling's solution?
A blue solution of complexed copper (II) ions dissolved in sodium hydroxide.
39
What is Benedict's solution?
A blue solution of complexed copper (II) ions dissolved in sodium carbonate.
40
Describe a positive test for an aldehyde when heated with Fehling's or Benedict's solution.
The copper (II) ions are reduced to a brick-red precipitate of copper (I) oxide.
41
Give the half equation to show how the brick red precipitate from Fehling's solution is formed.
Cu2+(aq) + e- → Cu+(s)
42
What is the product of an aldehyde heated with acidified dichromate (VI) ions?
A carboxylic acid.
43
What colour change will you observe when you heat and aldehyde with acidified dichromate (VI) ions?
Orange to green.
44
Why won't ketones oxidise with acidified potassium dichromate ions?
It is not a strong enough oxidising agent.
45
What would an aldehyde reduce to?
A primary alcohol.
46
What would a ketone reduce to?
A secondary alcohol.
47
Give an example of a strong reducing agent.
LiAlH4, lithium aluminium hydride in dry diethyl ether.
48
What happens when you react LiAlH4 with water.
It bursts into flames.
49
What happens when you heat iodine with a carbonyl that contains a methyl carbonyl group?
You get a yellow precipitate of triiodomethane (CHI3) and an antiseptic smell.
50
What is a methyl carbonyl group and name the aldehyde that contains one.
A carbon with a methyl group and a carbonyl group attached to it. Ethanal.
51
Name the group other than methyl carbonyl that iodine forms a yellow precipitate with.
CH(CH3)OH
52
Which alcohols form triiodomethane when reacted with iodine?
Ethanol, secondary alcohols with the hydroxy group on carbon 2 but no tertiary alcohols.
53
Describe the test for a CH(CH3)OH group using sodium hydroxide.
Iodine solution is added to a small amount of an alcohol, followed by just enough sodium hydroxide solution to remove the colour of the iodine. If nothing happens in the cold, it may be necessary to warm the mixture very gently.
54
Describe the test for a CH(CH3)OH group using sodium chlorate solutions.
Potassium iodide solution is added to a small amount of an alcohol, followed by sodium chlorate(I) solution. If no precipitate is formed in the cold, it may be necessary to warm the mixture very gently.
55
What are the two products formed when there is a positive test for a CH(CH3)OH group?
Triiodomethane and a carboxylate ion.
56
Which functional group to carboxylic acids contain?
The carboxyl group, -COOH.
57
How do you name a carboxylic acid?
Find and name the longest carbon chain and add -oic acid.
58
What type of cards are carboxylic acids?
Weak acids.
59
What effect does the polar nature of carboxylic acid molecules have on their boiling points?
It means they have very high boiling points.
60
Why are carboxylic acids very soluble in water?
They can form hydrogen bonds with water molecules.
61
What happens to the solubility of a carboxylic acid as chain length increases?
Solubility decreases.
62
What can form in pure liquid carboxylic acids?
Dimers.
63
What are dimers?
When a molecule hydrogen bonds with just one other module.
64
Explain the effect of dimers on boiling point?
Forming dimers effectively increases the size of a molecule, increasing the intermolecular forces and therefore increasing the boiling point.
65
State two methods of forming carboxylic acids.
Oxidation of primary alcohols and aldehydes. Hydrolysis of nitriles.
66
How can you react a nitrile into a carboxylic acid?
Reflux it with dilute hydrochloric acid. Ammonium chloride also forms.
67
What happens when you mix ethanoic acid with sodium hydroxide?
It is neutralised by the aqueous alkali to form sodium ethanoate and water.
68
What are the products of a reaction between ethanoic acid and sodium carbonate or sodium hydrogen carbonate?
Sodium ethanoate, carbon dioxide and water.
69
What happens when you try to reduce a carboxylic acid with LiAlH4?
It reduces straight back to an alcohol.
70
Give all the products of a reaction between a carboxylic acid and phosphorus (V) chloride.
An acyl chloride, POCl3 and HCl.
71
How could you estimate the concentration of a carboxylic acid?
Titrate it against sodium hydroxide and use phenolphthalein as an indicator. For citric acid, the end point is when the indicator has turned pink for at least 30 seconds.
72
What forms when you react alcohol with carboxylic acids?
Esters.
73
What are the reactants conditions for producing an ester?
Heat and reflux carboxylic acid with an alcohol in the presence of an acid catalyst (such as conc H2SO4).
74
What type of reaction occurs between alcohols and carboxylic acids?
Condensation reactions.
75
Why do you have to distilled the products of esterification?
Because it is a reversible reaction.
76
How would you remove any excess acid left over form the production of an ester?
Mix it with sodium carbonate solution and use a separating funnel to collect the organic layer at the top.
77
Give two uses of the ester ethyl ethanoate.
Solvent in chromatography and pineapple flavouring.
78
What is the functional group of an ester?
-COO-
79
How do you name an ester?
The first bit of the name is the alkyl group origination from the alcohol and the second part is the carboxylate ion name from the carboxylic acid.
80
Give to two types of hydrolysis used to form alcohols from esters.
Acid and base hydrolysis.
81
Explain acid hydrolysis of an ester.
It is the reverse of the condensation reaction that produced the ester. You reflex the ester with dilute acid and lots of water to favour the equilibrium position. This produces an acid and an alcohol.
82
Explain base hydrolysis of an ester.
You reflux the ester with dilute alkali such as sodium hydroxide. This produces a carboxylate ion and an alcohol.
83
What type of chemicals are vegetable oils and animal fats?
Triesters.
84
How are trimesters made?
The esterification of glycerol (propane-1,2,3-triol) with fatty acids (long chain carboxylic acids). Each OH group on the glycerol is replace with a fatty acid joined by an ester bond.
85
How can you make soap from fat?
Hydrolyse fats and oils with NaOH.
86
Outline the process of making soap.
Heat fat or oil with conc NaOH and allow it to cool. Then add saturated NaCl solution and the soap will separate out as crust on the surface of the liquid. Amazing.
87
What is the name for the process where alcohol is reacted with esters to make new esters?
Transesterification.
88
State two practical uses for transesterification.
Making low fat spreads and making biodiesel from vegetable oils.
89
Explain the advantages of using transesterification over hydrogenation to make low fat spreads.
Hydrogenation produces trans fats which are very unhealthy. Meanwhile transesterification converts vegetable oils into different esters with higher boiling points than don't contain trans isomers.
90
Explain the advantages of using transesterification to make biodiesel.
It is a renewable source of energy and is made of waste products.
91
Name the reagents and products for the reaction producing biodiesel.
Triglyceride and methanol are used make methyl ester (biodiesel) and glycerol.
92
Name two reagents required to make polyesters.
Dicarboxylic acids and diols.
93
Which chemical group join dicarboxylic acids and diols in a polyester?
The ester link.
94
Give three properties of polyester fibres.
Strong, flexible, abrasion-resistant.
95
Where are polyesters used?
In clothes, carpets and plastic bottles once traded.
96
What are acyl (acid) chlorides?
Chemicals that have the COCl group.
97
Give the general formula for an acyl chloride.
Cn H2n-1 OCl.
98
What is the naming suffix for acyl chlorides?
-oyl chloride.
99
What makes acyl chlorides so reactive?
They easily lose their chlorine.
100
What happens when you react an acyl chloride with water at room temperature?
A vigorous reaction occurs, producing a carboxylic acid and HCl.
101
What happens when you react an acyl chloride with alcohols at room temperature?
A vigorous reaction occurs, producing an ester and HCl.
102
What happens when you react an acyl chloride with ammonia at room temperature?
A violent reaction occurs, producing an amide and HCl.
103
What happens when you react an acyl chloride with amines at room temperature?
A violent reaction occurs, producing an N-substituted amide and HCl.
104
In general, what happens when an acyl chloride reacts with an organic molecule?
The Cl is substituted by an oxygen or nitrogen group and hydrogen chloride fumes are given off.
