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Chemistry A Level Pearson's Edexcel > Organic Chemistry > Flashcards

Organic Chemistry Flashcards

(105 cards)

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1
Q

What is a chiral molecule?

A

A chiral molecule is a molecule containing a chiral carbon atom, which has four different groups bonded to it.

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2
Q

What is the name of a chiral isomer?

A

Enantiomer.

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3
Q

What is the key property to enantiomers?

A

Enantiomers rotate the plane of plane-polarised light by equal amounts but in opposite directions.

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4
Q

What happens to a 50:50 mixture of both optical isomers?

A

A raecemic mixture occurs where they solution is not optically active as both the rotations cancel out.

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5
Q

Explain why Sn1 nucleophilic substitution always results in a raecemic mixture.

A

The carbocation intermediate is trigonal planar therefore the OH- can attack from two sides that result in different isomers which produces a 50:50 mixture of both isomers.

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6
Q

Explain why in Sn2 nucleophilic substitution the product is always the opposite enantiomer to the reactant.

A

The OH- always attacks from the same side therefore the molecule undergoes chiral inversion.

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7
Q

What happens in nucleophilic addition in terms of chirality?

A

The CN- can attack from either side which results in a raecemic mixture.

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8
Q

Explain why carbonyl compounds have slightly higher boiling points that equivalently sized alkanes.

A

Carbonyl compounds are polar therefore they form permanent dpdp forces which are stronger than london forces.

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9
Q

Describe and explain the trend in solubility for carbonyl compounds.

A

Small compounds (C<5) tend to be miscible with water as they can form hydrogen bonds by as they get larger, more hydrogen bonds are disrupted with water than there are formed with the carbonyl compound which decreases the solubility of that compound dramatically.

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10
Q

What can 2,4-DNPH be used to test for? What is the colour change in a positive test?

A

It can be used to test for a C=O bond in a compound. The colour change in a positive test is yellow/orange solution -> yellow/orange precipitate

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11
Q

What is the product when a primary alcohol is fully oxidised in acidic conditions?

A

Carboxylic acid (-COOH group is protonated)

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12
Q

What is the product when a primary alcohol is fully oxidised in alkaline conditions?

A

Carboxylate salt (-CO2 is deprotonated)

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13
Q

Describe the conditions required to make a carboxylic reaction from a primary alcohol.

A

Solution must be heated under reflux.
Potassium dichromate(VI): K2Cr2O7(aq).
Dilute sulfuric acid: H2SO4(aq).
Acid must be distilled out at the end

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14
Q

What is the colour change when you oxidise a primary alcohol into a carboxylic acid?

A

Orange to Green

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15
Q

Name the product when a primary alcohol is oxidised by Tollens’ reagent and the colour change that occurs.

A

It forms a carboxylate salt and forms a silver mirror on the inner surface of the test tube.

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16
Q

Describe the preparation of Tollens’ reagent.

A

Add NaOH to AgNO3 to form Ag2O ppt.
Re-dissolve ppt in NH3 dropwise.

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17
Q

Name the product when a primary alcohol is oxidised by Fehling’s/Benedict’s solution and the colour change that occurs.

A

It forms a carboxylate salt and the colour change is from a blue solution to a red precipitate.

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18
Q

What does lithium aluminium hydride (LiAlH4) do?

A

It reduces carbonyl compounds into their respective alcohols as it acts as a source of H- ions.

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19
Q

What is the necessary conditions when using lithal?

A

Lithal must be dissolved in a dry ether as this prevents it from hydrolysing: LiAlH4 + 4H2O -> LiOH + Al(OH)3 + 4H2

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20
Q

Describe roughly what occurs in the “iodoform reaction”.

A

A carbonyl compound is oxidised to a carboxylate salt.

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21
Q

What are the products in an iodoform reaction.

A

A carboxylate salt and iodoform (CHI3)

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22
Q

What organic molecules can be oxidised by iodine? (Iodoform reaction)

A

Ethanol
Ethanal
Methyl secondary alcohol
Methyl ketone

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23
Q

Describe the products of nucleophilic addition reaction of a ketone with HCN/KCN.

A

It forms a nitrile compound with an alcohol group.

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24
Q

Describe the nucleophilic addition mechanism of a ketone with HCN/KCN?

A

First step:
CN from KCN acts as a nucleophile and C=O bond breaks.

Second step:
O- takes H+ from HCN.

Overall:
CN- from KCN is regenerated and HCN is used up.

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25
Describe the conditions that are required for nucleophilic addition.
HCN and KCN (which is what edexcel want you to write) You could also use KCN and H2SO4 (this generates HCN in the situation which is safer) or you could use HCN with a pH of 9.21 (which maintains a equilibrium of HCN dissociation that keeps HCN and CN- concentrations large at all times)
26
Explain why carboxylic acids have higher boiling points that equivalently sized alkanes and alcohols.
Carboxylic acids form strong hydrogen bonds. They are also polar therefore form dpdp forces. The molecules can also pair up to form dimers which doubles the strength of their london forces. Overall this means that their intermolecular forces are quite strong.
27
Describe the trend in solubility for carboxylic acids.
Small compounds (C<5) tend to be miscible with water as they can form hydrogen bonds but as they get larger, more hydrogen bonds are disrupted with water than there are formed with the carboxylic acid which decreases the solubility of that molecule dramatically.
28
What is made when a nitrile is hydrolised with HCl or NaOH (give answer for both)?
A carboxylic acid when heated under reflux with dilute HCl and a carboxylate salt when heated under reflux with NaOH.
29
What is the product when a carboxylic acid reacts with PCl5 and what are the observations?
An acyl chloride. Steamy white fumes which turn damp blue litmus paper red.
30
What can PCl5 be used to test for?
An OH group.
31
What forms when a carboxylic acid reacts with an alcohol? What other condition is required for this reaction to work?
An ester. Concentrated sulfuric acid.
32
How can an acyl chloride form a carboxylic acid and describe the solution it forms.
It can react with water to create a carboxylic acid. This creates a very acidic mixture as a weak acid is formed (carboxylic acid) and a strong acid is formed (HCl).
33
What forms when an alcohol reacts with an acyl chloride and why is this the preferred method of creating this type of compound?
It makes an ester and its preferred because it is the fast and complete method. The other way to make an ester with an alcohol is by reacting it with PC5 and then another alcohol.
34
What is formed when an acyl chloride reacts with ammonia?
Amides
35
What is the name of an ester derived from and which order do they go in? (give an example)
The alcohol derived part and then the acid derived part. e.g. Methyl ethanoate or Ethyl butanoate
36
Explain the low boiling points in esters.
Moderate london forces. Permanent dpdp forces. No hydrogen bonding.
37
Explain the difference in aqueous solubility of esters and alkanes
Ester group can form H bonds whereas the carbon chains cannot.
38
Describe how esters can be made from carboxylic acids and why this method is not efficient. Also Explain.
Carboxylic acids can react with alcohols in the presence of concentrated sulfuric acid to form esters. Carboxylic acids aren't very susceptible to nucleophiles and alcohols are weak nucleophiles. The reaction is also reversible as water can hydrolise the product therefore the reaction is slow, incomplete and has a low % yield.
39
What is the good and bad way of forming esters? (e.g. methyl ethanoate)
Bad way: Alcohol + carboxylic acid (w/ H2SO4) -> ester + water Slow, incomplete, low % yield Good way: Acyl chloride + alcohol -> ester + HCl Fast, complete, high % yield
40
How can an ester be converted back into carboxylic acids and alcohols?
Esters can be hydrolysed in acidic conditions but this is a bad method as it has a low % yield due to the reaction being reversible.
41
What is formed when esters are hydrolysed in alkaline conditions? What is good about this reaction?
A carboxylate salt and an alcohol. The reaction is irreversible and OH is a good nucleophile therefore it is fast and has a high % yield.
42
What is the better method of hydrolysing esters? Heating under reflux with HCl or NaOH.
Heating under reflux is with NaOH is better as this is fast, complete and has a high % yield. Doing this with HCl is slow, incomplete and therefore has a low % yield.
43
What is the name of the reaction that forms polymers from ester polymers?
Condensation polymerisation.
44
What are the two ways that polyesters can be formed and what are their side products? (must be from one monomer)
Molecules with a COOH group and an OH group. This produces water. Molecules with a COCl group and COOH group. This produces HCl.
45
What two monomers can be used to make polyesters? (there are two pairs)
A dicarboxylic acid and a diol. Or a diol and a diacyl chloride.
46
Define a hydrocarbon.
A molecule that is made up of only hydrogens and carbons.
47
Define empirical formula.
The simplest whole number ration of atoms of each element in a compound
48
Define molecular formula.
The true number of atoms of each element in a compound.
49
Define general formula.
All members of a homologous organic series follow the general formula. e.g. alkanes CnH2n+2
50
Define structural formula.
Shows the structural arrangement of atoms within a molecule. e.g. CH3CH2COCH3
51
Define displayed formula.
A formula/diagram that shows every atom and every bond in an organic compound.
52
Define skeletal formula.
A formula/diagram that shows only the bonds in a compound and any non-carbon atoms. The vertices are carbon atoms and hydrogen is assumed to be bonded to them unless stated otherwise.
53
Define homologous series.
A group of organic compounds of which follow a general formula and react in similar ways. Typically as the size of the compound increases, the boiling points tend to increase as well.
54
What is meant by an addition reaction?
In an addition reaction, the reactants combine to form a single product.
55
What is meant by a substitution reaction?
In a substitution reaction, one functional group is replaced by a different functional group.
56
What is meant by an oxidation reaction?
A species loses at least one electron, and therefore is oxidised.
57
What is meant by a reduction reaction?
A species gains at least one electron, and is reduced.
58
What is meant by a polymerisation reaction?
A reaction in which many small molecules, known as monomers, join together to form a long, repeating molecule called a polymer.
59
Define isomerism.
Isomers are molecules with the same molecular formula but a different arrangement of atoms within the molecule.
60
Define structural isomers.
Structural isomers have the same molecular formula but a different structural arrangement of atoms. They can be straight chains or branched chains by will have the same molecular formula. e.g. butane and (2-)methyl propane.
61
Define stereoisomers and more specifically, E-Z isomers.
Stereoisomers have the same structural formula but have a different spatial arrangement of atoms and bonds. E-Z isomerism is a type of stereoisomerism, which occurs due to the limited rotation around a double carbon bond.
62
Describe the CIP priority rules when dealing with E-Z isomerism.
There is a priority of different groups in molecules that an display E-Z isomerism. The atom or group on each side of the double bond with the higher Ar or Mr is given the higher priority . These groups are used to determine if it is the E or Z isomer.
63
Describe Cis-Trans isomerism and how it differs from E-Z isomerism.
Cis-Trans isomers are the same as E-Z in terms of the priority rules. The difference is that if a hydrogen atom is being compared, then its a Cis-Trans isomer; otherwise its an E-Z isomer.
64
What is the general formula for alkanes?
CnH2n+2
65
What is meant by a saturated hydrocarbon?
A hydrocarbon that has no double bonds as every carbon has as many hydrogens bonded to it as possible.
66
Describe the function of catalytic converters and how they remove harmful products from combustion of fuels in vehicles.
Catalytic converters use a rhodium or platinum catalyst to convert compounds such as NOx,CO or HC into safer compounds such as H2, H2O or CO2.
67
Define free radical and how it is represented in chemical equations.
A free radial is a species with an unpaired electron and is represented with a single dot.
68
In what process are free radicals formed in? (Not FRS, be more specific)
A free radical is formed in the process of homolytic fission of a covalent bond.
69
Write an equation of the combustion of methane in excess oxygen.
CH4 + 2O2 -> CO2 + 2H2O
70
Write an equation of the combustion of methane in insufficient oxygen.
2CH4 + 3O2 -> 2CO + 4H2O
71
Name the three steps of free radical substitution.
Initiation, Propagation, Termination
72
Describe what happens in the first step of free radical substitution. Include the relevant equations.
The halogen is broken down in the presence of UV light Cl2 -> 2Cl*
73
Describe what happens in the second step of free radical substitution. Include the relevant equations.
A hydrogen is replaced and the Cl• radical reformed as a catalyst. Cl• + CH4 -> •CH3 + HCl •CH3 + Cl2 -> CH3Cl + Cl•
74
Describe what happens in the third step of free radical substitution. Include the relevant equations.
Two radicals join to end the chain reaction and form a stable product. *CH3 + *CH3 -> C2H6 2Cl* -> Cl2 *CH3 + *Cl -> CH3Cl
75
Explain why free radical substitution is inefficient.
The yield is extremely low. This is because the reaction can continue and replace all the hydrogens with halogens. It is also low yield due to the fact that the termination productions also produce longer organic chains therefore it could continue to produce many chains differing in length that isn't desired. Another factor is that there is a large mixture of molecules at the end of the process which creates a large challenge in separating out the desired molecules.
76
When does optical isomerism occur?
Optical isomerism is a result of chirality in molecules with a single chiral centre.
77
What are optical isomers?
Molecules with chiral centre(s) that have asymmetric carbon atom(s) and they are non-superimposable mirror images.
78
What is the difference between an aldehyde and a ketone functional group?
Aldehyde groups have C=O bonds at the end of the carbon chain whereas ketones have the C=O bonds in the middle of the chain.
79
Explain why aldehydes and ketones aren't able to form intermolecular hydrogen bonds between themselves and hence state the only existing type intermolecular forces between them.
Aldehydes and ketones don't have a delta+ hydrogen atom therefore they do not form hydrogen bonds between molecules. They only type of intermolecular force which exists between their molecules are van der Waals forces/London.
80
What is the carboxylic acid functional group?
COOH
81
Describe the production of a carboxylic acid from a nitrile.
The nitrile is heated under reflux with dilute hydrochloric acid which produces the free carboxylic acid.
82
Briefly describe a reaction between a carboxylic acid and lithium aluminium hydroxide.
The carboxylic acid is reduced by the H- ions from lithal which creates its respective aldehyde and then into a primary alcohol.
83
What is the functional group of an acyl chloride?
COCl
84
What is the functional group of an ester?
- COO - (O between two Rs and a C=O on one of the carbons attached to the other O)
85
What is the reaction between amines and carboxylic acids?
They produce N-substituted amides which are amides that have R groups instead of hydrogen atoms attached to the nitrogen.
86
What is the general formula for alkenes?
CnH2n
87
Explain what is meant by the term 'unsaturated' when talking about alkenes and cycloalkenes.
Alkenes and cycloalkenes have at least one double bond between carbons.
88
Describe the bonding in alkenes in terms of σ- and π- bonds.
There are σ- and π- bonds in the carbon-carbon double bonds and then only σ- bonds in any single bonds between two carbons on carbon and hydrogen atoms.
89
What is meant by the term 'electrophile'?
A species that acts as an electron pair acceptor.
90
Name the reactants and conditions required when forming an alkane from alkenes.
Hydrogen in the presence of a nickel catalyst. 150*
91
What are the reactants and conditions required when forming dihalogenoalkanes from alkenes?
Liquid bromine or bromine water. RTP
92
What are the reactants and conditions required when forming halogenoalkanes from alkenes?
Hydrogen halides. RTP
93
What are the reactants and conditions required when forming alcohols from alkenes?
Steam + acid catalyst (phosphoric (V) acid)
94
What are the reactants and conditions required when forming a diol from alkenes?
Oxidising agent (potassium manganate (VII)), dilute H2SO4 and hydrogen.
95
Name any observations when creating a diol from alkenes in acidic conditions.
Purple to colourless
96
Describe the test for a C=C double bond in organic compounds.
Take the sample of the organic compound and add bromine water. Bromine water is originally brown and in the presence of a C=C double bond, the solution would turn colourless.
97
Describe the conditions required to form a polymer from alkenes.
Heat and pressure
98
Define the term 'nucleophile'.
An electron pair donor
99
Describe the reactants and conditions required to produce alcohols from halogenoalkanes.
Dilute substitution with dilute potassium hydroxide or sodium hydroxide dissolved in water. Heat under reflux
100
Describe the reactants and conditions that produce alcohol and precipitate from halogenoalkanes.
Silver nitrate solution
101
Describe the reactants and conditions required to form nitriles from halogenoalkanes.
Potassium cyanide (KCN)
102
Describe the reactants and conditions required to product amines from halogenoalkanes.
Ammonia
103
Describe the reactants and conditions required to produce alkenes from halogenoalkanes.
Concentrated potassium or sodium hydroxide dissolved in ethanol. High temperature
104
Describe the trend of reactivity of halogenoalkanes in terms of type (1*, 2* or 3*)
Primary is the least reactive and tertiary is the most reactive because the collision needs to occur in the correct orientation for primary halogenoalkanes whereas no collision is necessary for tertiary to create the carbocation.
105
Describe the trend of reactivity of halogenoalkanes in terms of the halogen it has.
Chloroalkanes are the least reactive because the C-Cl bond is the strongest and iodoalkanes are the least reactive because the C-I bond is the weakest. N.B. : The trend has nothing to do with electronegativity.

Chemistry A Level Pearson's Edexcel (17 decks)

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