Alkanes and Organic Chemistry

  • Created by: Pope1912
  • Created on: 19-03-15 10:36


Count the carbon atoms in the longest continuous chain.

1  meth-              4 but-

2  eth-                 5 pent-

3 prop-                6 hex-

When naming alkenes look at the position of the double bond.

      H    H    H    H    H

H - C - C = C - C - C - H            Pent-2-ene

      H    H    H    H    H

If there is more than one double bond it gets the suffix -diene. The stem of the name also gains an a eg. Penta-. The number are infornt when more than one double bond is present. eg. 1, 3 butadiene

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General formula.

An algerbraic formula that can describe any member of a family of compounds.

Empirical formula.

The simplest ratio of each atoms of element in a compound.

Molecular formula. 

The actual number of atoms of each element in a molecule.

Structural formula.

Shows the atoms carbon by carbon with attached hydrogens and functional groups.

Displayed formula.

Shows how are the atoms are arranged and all the bonds between them. 

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Structural Isomerism

Structural Isomer - has the same molecular formula but the atoms are connected in different ways.

Chain isomers - have a different arrangement of the carbon skeleton. Some are straight chains and others are branched in different ways. 

Positional isomers - have the same skeleton and the same atoms or groups of atoms. The difference is the atom or grouo of atoms is attached else where.

Functional group isomers - have the same atoms arranged into different functional groups.

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Alkanes and Petroleum

Alkanes are saturated hydrocarbons.

Alkanes have the general formula CnH2n+2. Every carbon has four bonds. It is impossible for a carbon atom to have more than four bonds so the alkanes are saturated.

Cycloalkanes have a ring of carbons ecah with two hydrogens attatched. Cycloalkanes have the general formula CnH2n but are still saturated.

Crude oil is is mainly alkanes. They range from tiny chains to huge ones. As a whole crude oil is not very useful but you can seperate it into useful fractions by fractional distillation.

Crude oil is vapourised at around 350 degrees. The vapour rises and condenses at different points where it is tapped off. The longer the chain, the higher the boiling point, the lower down it condeses. hydrocarbons with the lowest boiling points don't condense and are drawn off as gases at the top. 

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Alkanes and Petroleum

Heavy fractions can be cracked into smaller molecules.

People want lots of light fractions like petrol. These popular fractions are much more valuable. To meet this demand the less popular, heavy fractions are cracked to make smaller molecules. This involves breacking the C-C  bond. 

Thermal cracking.

High temperatures and pressure. Produces a lot of alkenes. Alkenes are used to make large amounts of valuable products like polymers. 

Catalytic cracking.

Makes mostly motor fuels and aromatic hydrocarbons. Zeolite catalyst. HIgh temperature and slight pressure. Catalyst saves money as temperature and pressure is decreased whilst the reaction speed is greater.

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Alkanes as fuel

Alkanes are useful fuels. If you burn alkanes in pleanty of oxygen a combustion reaction occurs producing water and carbon dioxide.

If alkanes arent burnt in plenty of oxygen incomplete combustion occurs which results in carbon monoxide being produced. This carbon monoxide binds to sites on the haemoglobin molecules which then prevents oxygen binding and being carried around the body.

Unburnt hydrocarbons and oxides of ntrogen contribute to smog.

NOx are produced when the high pressures and temperatures of the car engine cause the nitrogen and oxygen to react together.

These oxides react in the presence of sunlight to form ground level ozone which can cause respiratory problems and lung damage.

Catalytic converters on cars remove unburnt hydrocarbons and oxides of nitroge from the exhaust. 

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Alkanes as fuel

Sulphur Dioxide

Acid rain is caused by burning fossil fuels that contain sulphur. The sulphur burns to produce sulphur dioxide gas which then enters the atmosphere, dissolves in moisture, and is converted into sulphuric acid.

Acid rain destroys trees and vegetation as well as corroding buildings and statuses and killing fish in lakes. This is removed from power station flue gases using calcium oxide. 

Burning fossil fuels contributes to global warming. 

Greenhouse gases stop some of the heat from the sun from escaping back into space. This is the greenhouse effect. 

An increase in carbon dioxide is enhancing this greenhouse effect causing global temperatures to increase.

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Alkanes as fuel

Carbon dioxide isn't the only greenhouse gas.

Some of the electromagnetic radiation from the sun reaches the earth is absorbed and then the earth re-emits it as infrared radiation.

Various gases in the troposphere absorb some of this radiation and re-emit it in all directions. This is the greenhouse effect.

The three main greenhouse gases are carbon dioxide, methane and water vapour.

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