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14.Organic Chemistry

Fractional distillation of crude oil (“Petroleum”)

This is where it all starts. Fossil fuels (coal, oil, natural gas (mainly methane)) are made up of molecules with carbon chains of different lengths.

They burn in very exothermic reactions which is what makes them excellent fuels.

A hydrocarbon is a molecule made up of hydrogen and carbon.

Eg. Methane - molecular formula:

Structural formula:

Butane - molecular formula:

Dot and cross diagram:

Structural formula:

14. Organic Chemistry

Crude oil is a mixture of hydrocarbons which are separated by fractional distillation (which makes use of the fact that the H-Cs have different boiling points):

NB. Each of the collections of HCs on the right of the diagram are called “fractions”, eg. Refinery gases.

The fractions can be further processed to produce more useful and reactive molecules by the process of....


Cracking

Longer chain HCs are broken up using high temperatures, pressures and catalysts.

Eg. Decane

Structural formula:

Possible products:

Dot and Cross diagrams:


When small alkanes are cracked, hydrogen can be produced:

Eg. Ethane

EQN:

CC pp247/249 All Qs

CC p249 Q1-6


Homologous SeriesThese are:

families of similar organic molecules with the same functional group

molecules with the same general formula

compounds with similar chemical properties

compounds with gradually changing physical properties, eg. melting points slowly increase as a chain gets longer.

We are going to look at the following homologous series:

I. AlkanesII. AlkenesIII. AlcoholsIV. Carboxylic acids

I. The Alkanes

HCs joined together by single covalent bonds.

General formula:

Draw the structural formula for 2 of the longer chained alkanes above:

Research: Find the boiling point for the first 10 alkanes, and add them to the table. Label them as solids (S), liquids (L) or gases (G) at room temperature.

The longer the chains, the stronger the intermolecular forces, so the higher the melting and boiling points.


The bonds in the alkanes are strong and hard to break, making them quite unreactive. There are 2 types of reaction than you must know...

1. Combustion

With plenty of oxygen, the products are carbon dioxide and water...

Eg. Pentane

With limited oxygen, carbon monoxide and even carbon can be produced...

Combustion is very exothermic, and explains why these compounds are used as fuels, eg. natural gas (mainly methane) in the home, and butane/propane as camping gases, octane and diesel in vehicles.


2. Substitution reactions with chlorine (and other halogens)

Alkanes react with halogens and their hydrogen atoms are slowly replaced. These are photochemical reactions. The classic and explosive example is...

Methane and chlorine (in UV light)

EQNs:

The final mixture would contain all of the above compounds. These substitution reactions give multiple products (which means that they are not a good way to make a specific compound.

How would we separate the products from this type of reaction?

CC p253 Q1-5


Isomers

Structural isomers are molecules that have the same molecular formula but a different structural formula.

eg. Pentane

CC p253 Q6


II. Alkenes

These are more reactive HCs, as they contain a Carbon-Carbon double bond. They are made by cracking (see earlier).

General Formula:

Try to draw 2 structural formulae from the above list:


Draw the structural isomers of butene:

NB. Alkenes are called “unsaturated” molecules as they contain the C=C double bond (alkanes are “saturated”).


Reactions of the alkenes (“addition” reactions)

Note: Alkenes burn with a yellow flame due to incomplete combustion, but this is not an important reaction of the alkenes. They are not used as fuels. Interesting reactions are...

1. Test for unsaturation

If the alkenes come into contact with bromine water, decolourisation results...

Eg. Ethene with bromine water

EQN:

Indicate the colour of reactants and products.

The bromine is “added” to the double bond.

2. With hydrogen

The hydrogen adds to the double bond, in the presence of a catalyst at high temperature producing the alkane...

Eg. Propene with hydrogen

EQN:

This reaction is used to convert unsaturated vegetable oils into margarine.

3. With steam

Here, an alcohol is produced...

Eg. But-1-ene

EQN:


4. Polymerisation

Alkenes can join together to form long chains in a process called “polymerisation”.

Eg. Ethene at high temperature and pressure, and and oxygen catalyst.

EQN:

Uses: “plastic” bags, bottles, bins, kettles,...

This is called “addition polymerisation” as many alkene undergo addition reactions to form the polymer. Other examples:

Monomer Polymer Uses

Propene

Chloroethene

Phenylethene


Environmental problems and possible solutions

Disposal of polymers is a problem. Why?

What can be done to overcome this problem?

CC p255 Q1-5CC p265 Q1-5

Tetrafluoroethene

Monomer Polymer Uses


III. Alcohols

The functional group is -OH and the general formula is:

Write the formula and name for each of the following alcohols:


Making Ethanol

1. Fermentation

Glucose in the presence of yeast (an enzyme catalyst) and in the absence of air breaks down to make ethanol and carbon dioxide:

EQN:

2. The hydration of ethene:

We saw this reaction before. Steam will add the the C=C double bond.

EQN:

The first method produces a mixture of alcohol and water; the second, pure ethanol.

Reactions of Ethanol

1. Oxidation

In the presence of oxygen (atmospheric or otherwise), ethanol is oxidised to Ethanoic Acid:

EQN:

Oxidation can also be achieved using the oxidising agent potassium dichromate(VI), which changes from orange to green in the process.


2. Cracking of ethanol to make ethene

Labelled diagram:

EQN:

NB. Suck back

Use of Ethanol

1. It is used as a solvent for organic substances that are insoluble in water, eg. in pens, paints, glues, aftershave, perfume,...

2. It is used as a fuel for vehicles and can be produced on a large scale by the fermentation of sugar cane (sustainable energy).

The combustion EQN:

3. In alcoholic drinks such as wines, beer and cider, and stronger beverages produced by distillation of fermented ethanol, eg. whisky, vodka and liquours.

CC p257 Q1-614. Organic Chemistry

IV. Carboxylic Acids

The functional group:

General formula:

Give the formula and name of the following:


Important reaction involving carboxylic acids:

1. They are all weak acids, as they are only partially dissociated when they dissolve in water:

EQN:

They react with alkalis is the classic manner:

EQN:

Name the product.

2. As we saw before, they can be produced by oxidation of alcohols by atmospheric oxygen or potassium dichromate(VI).

3. They are used with alcohol to make ESTERS.

Esters are volatile, sweet or “fruity” smelling substances used in oils, perfumes and as flavourings in food.

They are produced when an alcohol and a carboxylic acid react:


Try to name the following:

NB.1. Esterification is a reversible reaction.2. An acid is used as a catalyst (hydrochloric or sulphuric acid)3. These molecules contain an “ester link”. Identify it.

CC p259 Q1-6Exam Questions CC pp260-261


Natural and Synthetic macromoleculesMacromolecules are very large structures made up of many small units connected by covalent bonds, eg. graphite, diamond, silicon(IV)oxide and polymers

Synthetic polymersWe have already seen polyalkenes, which are an example of addition polymerisation.

Another example of polymerisation is “condensation polymerisation”.

Nylon (a polyamide)

This synthetic polymer is formed by a condensation polymerisation reaction:

The monomers:

Abbreviations:

The reaction:

A molecule of water is “condensed every time an “amide link” is formed (unlike in polyalkenes).


Terylene (a polyester)

The monomers:

The reaction:

Abbreviation:

Use CC to find out some uses of these polymers:Nylon Terylene


Problems caused by plastics (synthetic polymers) and possible solutions

The production of these polymers has a negative effect on the environment:

A significant percentage of the world’s fossil fuels is used to make them. This uses up a vital resource and adds to global warming.

Plastics are non-biodegradable - they last for many years, causing short and long term problems for land and sea animals.

Plastics cannot be burnt, as they produce toxic gases.

Solutions:

Use sustainable energy sources in their production Use sustainable substances in their production (not fossil fuels) Recycle Use biodegradable polymers Use less plastic - develop alternative and more environmentally friendly materials

http://www.youtube.com/watch?v=Q6hzhKmw4EY

http://www.youtube.com/watch?v=kLic5G5-vWM

http://www.youtube.com/watch?v=LgP8Du7DZW8

http://www.youtube.com/watch?v=CY2OuKLvzEE&feature=relmfu

CC p267 Q1-5

CC Read pp268-27114. Organic Chemistry

http://www.youtube.com/watch?v=Q6hzhKmw4EY

http://www.youtube.com/watch?v=kLic5G5-vWM

http://www.youtube.com/watch?v=LgP8Du7DZW8

http://www.youtube.com/watch?v=CY2OuKLvzEE&feature=relmfu

Natural PolymersThere are 3 natural polymers that we need to be aware of:

• Starch (carbohydrates)• Proteins• Fats

These are the main constituents of food.

Carbohydrates

Sugar molecules (produced by photosynthesis in plants) come together to form long chains in condensation polymerisation reactions:

Abbreviation:


Proteins

The building blocks (monomers) used to make proteins are amino acids:

Using abbreviations, what would the chain look like?

This is a condensation polymerisation reaction.

Indicate on the above chain where the link is between the molecules, and name it.

NB1. Proteins are natural polyamides.

NB2. Amino acids can be separated and identified using chromatography (see Year 10).


Fats

These are produced when glycerol and fatty acids react:

Again, this is condensation polymerisation.

The length and nature of the fatty acids will vary, giving a range of fats and oils.Identify the link between the molecules.


Hydrolysis of Natural Macromolecules

The word “hydrolysis” means “breaking up using water”.

Larger organic molecules are attacked by water, in the presence of acid (or alkali), and are broken into smaller pieces.

This is the reverse of the previous processes, and water is returned to the original molecules:

Starch Glucose (simple sugars)

Proteins Amino Acids

Fats Glycerol and fatty acids


+ H2O

Soap Manufacture

The basic process of making soap involves the alkaline hydrolysis of natural fats (using sodium hydroxide)

The soap is the collection of sodium salts of fatty acids.

Glycerol has hydrating properties and is often left in the soap.

CC Read pp272-277 and answer questionsExam Questions CC p278-279

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