AQA Chemistry A-Levels [Organic Chemistry]

chem

What is organic chemistry?

The study of carbon-containing compounds

What are the different ways in which you can represent organic compounds?

• General formula
• Empirical formula
• Molecular formula
• Structural formula
• Skeletal formula
• Displayed formula

What is nomenclature?

The systematic method of naming chemical compounds in accordance with established rules

What are the features of a homologous series?

• All members contain the same functional group
• All members have the same general formula
• Each subsequent compound in the series differs by a CH2 unit

What are the two types of organic compounds?

1. Aromatic skeletons (benzene rings)
2. Non-aromatic skeletons (straight chained/branched)

Define the term structural isomer

A molecule that has the same molecular formula but a different structural formula

Define the term stereoisomerism

Molecules that have the same molecular formula and same functional groups but a different arrangement of atoms in space

What is a curly arrow used to show?

The movement of a pair of electrons

What is a free radical?

A species that has an unpaired electron
Free radicals are very reactive molecules

What is fractional distillation?

The process of separating crude oil into groups of hydrocarbons with similar numbers of carbon atoms.
These groups are called "fractions"

*It's quite a common mistake that people say the groups of hydrocarbons are separated based on their boiling points

What is the first step in the process of fractional distillation?

Evaporation: Crude oil is heated until it is evaporated.

What happens to the vapour in fractional distillation?

The vapour is put into a fractionating column at the bottom and rises to the top.

Where is the temperature highest in the fractionating column?

The temperature is highest at the bottom of the column.

What happens to long chain hydrocarbons in fractional distillation?

Long chain hydrocarbons condense at the bottom and are collected as liquids.

Where do short chain hydrocarbons condense in the fractionating column?

Short chain hydrocarbons condense at lower temperatures nearer the top.

What is done with the collected fractions in fractional distillation?

The fractions are processed to create more useful products

What is cracking?

The process of converting alkanes into alkenes and shorter alkanes. Shorter alkanes are more valuable than longer ones (shorter alkanes are used as fuels!)

Outline the features of thermal cracking

• It uses high temperatures and high pressures
• It breaks alkanes into a high percentage of alkenes and comparatively few alkanes
• Done at around 1000C and 70 atm

Outline the features of catalytic cracking

• This process uses a catalyst

What are the products of complete combustion?

Carbon dioxide and water

What are the products of incomplete combustion?

Pure carbon

What are some common impurities from an internal combustion engine of a car?

• Nitrous oxides (NOx)
• Unburned hydrocarbons
• Carbon monoxide

Nitrous oxides react to form ozone at ground level

What does flue gas often contain?

Sulfur dioxide

Why is sulfur dioxide dangerous?

It dissolves in water to make sulfuric acid. This then falls as acid rain

What is flue gas?

Gasses that come out of chimneys. They are also produced as industrial waste

How can we remove sulfur dioxide?

By reacting it with either calcium oxide or calcium carbonate.
This is because sulfur dioxide and calcium oxide is basic.
The equation is:
CaO + SO2 ➔ CaSO3
CaCO3 + SO2 ➔ CaSO3 + CO2

What is the advantage of flue gas desulfurisation?

The sulfur dioxide is removed!

What are the disadvantages of flue gas desulfurisation?

• The CaSO3 produced is a solid

How can we remove harmful gasses from internal combustion engines?

Catalytic converters can remove unburned hydrocarbons and nitrous oxides from fuel.

What happens in initiation

and what conditions are needed?

What happens in propagation?

A free radical

What happens in termination?

When two free radicals react together to produce a molecule. Once this happens

What is a halogenoalkane?

A halogenoalkane (or haloalkane) is a halogenated alkane. This means that one or more of the hydrogen atoms in an alkane has been replaced by a halogen atom.

What are some of the properties of haloalkanes?

• They are polar molecules and contain polar bonds
• These polar bonds are important in their reactions
• Halogens are more electronegative than carbon

What is a nucleophile?

A molecule that is attracted to a (positive) nucleus.
Nucleo = "positive"
Phile = "Loving"
So

What makes a molecule a nucleophile?

Either the presence of lone pairs of electrons

What is an electrophile?

A molecule that is attracted to a pair of electrons
Electro = "Negative"
Phile = "Loving"
So

What happens in nucleophilic substitution?

When haloalkanes react with nucleophiles in a reaction

List the reactivity of haloalkanes

according to the halogen

What is elimination reactions?

When

What does reflux involve?

It involves using a reflux condenser (basically just a condensing tube from a distillation set up)

How can we promote an elimination reaction?

Use ethanol as the solvent instead of water.
Heat the reaction under reflux conditions

How can we promote a substitution reaction?

Use water as the solvent instead of ethanol.

What is a CFC?

A chlorofluorocarbon molecule.
They only contain carbon

What is the formula for ozone?

O3
(It is much less stable than O2)

How is ozone formed?

From oxygen (O2) and in the presence of UV light

What do CFC's undergo in the atmosphere?

They undergo photolysis

What does the process of photolysis produce?

A chlorine free radical (these then go on to react with ozone

Why were CFC's banned?

Because there was evidence that they were damaging the ozone layer

What do chain isomers differ in?

They differ in the arrangement of the hydrocarbon chain

What do position isomers differ in?

They differ in the position of their functional groups

What is unique about single covalent bonds

in terms of stereoisomerism?

What is unique about double covalent bonds

in terms of stereoisomerism?

What two conditions must an alkene fulfil in order to have cis/trans isomers?

1. The carbon atoms on the double bond must be attached to two different groups
2. At least one of those groups must be the same on both carbon atoms on the double bond

How can you name molecules using E/Z isomerism?

By using CIP priority rules.

How do you use CIP priority rules? List all the steps

1. Look at the atoms attached to the carbons on either side of the double bond
2. The element with the greatest atomic number is given the higher priority
3. If both high priority atoms are on the same side of the double bond

What is an alcohol?

Organic compounds that contain a hydroxyl functional group bonded to a carbon atom

What is the general formula for alcohols?

CnH2n+1OH
Where 'n' is number of carbon atoms

What are primary alcohols?

Where the -OH group is attached to a carbon atom that is bonded to only one alkyl group (for example another carbon atom)

What is a secondary alcohol?

The -OH is attached to a carbon atom that is bonded two to alkyl groups (e.g. two other C atoms)

What is a tertiary alcohol?

The -OH group is attached to a carbon atom that is bonded to three alkyl groups (e.g. three other C atoms)

Why do alcohols form hydrogen bonds?

The bond between the oxygen and hydrogen in the -OH group is polar (remember

What is the name of the chemical reaction that produces ethanol

industrially?

How is ethene typically obtained?

From the cracking of crude oil

What is the hydration reaction of ethene to produce ethanol?

C2H4 + H2O ➔ C2H5OH

Draw the mechanism for the hydration reaction

which produces ethanol from ethene and water

Other than hydration

what is another method for producing ethanol?

What is the equation for the fermentation of glucose

by yeast

How is ethanol separated from a fermentation mixture?

Through the process of fractional distillation

Why is fermentation of glucose a more costly method than hydration of ethanol?

The step required to purify ethanol in fermentation is more costly than hydration

What are biofuels?

Biofuels are renewable fuels derived from recently living biological materials

What are the advantages of bioethanol production?

1. Renewable - Ethanol is produced from crops that can be replanted and harvested repeatedly.
2. Lower net CO2 emissions - The crops used for ethanol production absorb CO2 from the atmosphere during their growth phase

What are the disadvantages of bioethanol production?

1. Engine modifications - Some engines may require adjustments to efficiently use fuels with high ethanol content.
2. Competition for land - Using agricultural land for fuel production can reduce the area available for food crops.

Why can ethanol fermentation be seen as carbon neutral?

This is because there is an equal amount of CO2 being absorbed

What is the equation for photosynthesis?

6CO2 + 6H2O ➔ C6H12O6 + 6O2

What is the equation for fermentation of glucose?

C6H12O6 ➔ 2C2H5OH + 2CO2

What is the equation for combustion of ethanol?

2C2H5OH + 6O2 ➔ 6H2O + 4CO2

Why isn't the whole process of ethanol fermentation actually carbon neutral?

1 - Fossil fuels being used to produce fertilisers for the crops (burning of fossil fuels release CO2).
2 - The total energy consumed by farm machinery during planting and harvesting

What is the equation for the complete combustion of ethanol when it is liquid?

C2H5OH(l)+ 3O2(g) ➔ 2CO2(g) + 3H2O(g)

How can the oxidation of alcohols be carried out?

Using acidified potassium dichromate.
The potassium dichromate can be acidified using dilute sulfuric acid

What does the extent of oxidation of alcohols depend on?

The structure of the alcohol — whether it is primary

Primary alcohols are oxidised to and then to ___ ____.

Primary alcohols are oxidised to aldehydes and then to carboxylic acids.

Secondary alcohols are oxidised to __ only.

Secondary alcohols are oxidised to ketones only.

Tertiary alcohols do not oxidise!

In the second stage of oxidation of primary alcohols

how do you isolate the aldehyde that is produced?

In the oxidation of primary alcohols

how do you isolate the carboxylic acid that is produced?

What is the structure of aldehydes?

Aldehydes have a hydrogen atom and one alkyl group attached to the carbonyl carbon

What is the structure of ketones?

Ketones have two alkyl groups attached to the carbonyl carbon.

What is the structure of carboxylic acids?

Carboxylic acids have a carboxyl functional group (COOH) attached to an alkyl group.

How can aldehydes and ketones be distinguished? Outline the steps.

Aldehydes and ketones can be differentiated using Fehling's solution and Tollens' reagent:

• Aldehydes reduce Fehling's solution from blue to brick-red Cu2O when warmed

Why were CFCs widely used?

They were used for reasons such as:

• High stability
• Low toxicity
• Non-flammability
• Volatility

Draw the mechanism for nucleophilic substitution for bromoethane with hydroxide ions

and draw the product formed

Draw the mechanism for electrophilic addition of ethene with bromine

and draw the product formed

Draw the mechanism for elimination of 2-bromopropane with hydroxide ions

and draw the product formed

Nucleophilic substitution is favoured in what kind of solvent?

In aqueous solution.
The OH- ions act as a nucleophile

Electrophilic elimination is favoured in what kind of solvent?

Ethanolic solution (Solution where ethanol is used as solvent).
The OH- ions act as a base

What is the general formula for alkanes?

CnH2n+2
Where 'n' is the number of carbon atoms

What is the general formula for alkenes?

CnH2n
Where 'n' is the number of carbon atoms

What is the C=C bond in alkenes described as being?

Regions of high electron density

What two types of bonds are in a C=C bond?

A pi bond

Why can't the C=C bond in alkenes rotate?

Because of the overlapping of the pi orbitals above and below the carbon atoms