OCR AS Chemistry F331: Organic Functional Groups

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  • Created on: 22-08-13 18:30
Preview of OCR AS Chemistry F331: Organic Functional Groups

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Hydrocarbons are compounds containing only carbon atoms and hydrogen atoms.
They are represented by the general molecular formula C xHy.
There are different types of hydrocarbons:
CH4 Methane Alkane
C2H4 Ethene Alkene
C6H6 Benzene Arene

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Alkanes are saturated hydrocarbons.
Saturated means they contain the maximum number of hydrogen atoms possible.
They have single bonds and no double bonds.
The general molecular formula of alkanes is CnH2n+2.…read more

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Structure of Alkanes
This is the full structural formula of heptane.
It shows all the atoms and all the bonds in the molecule.
The line represents a covalent bond, formed by sharing a pair of electrons, one from each
atom.…read more

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Branched Alkanes
Alkanes may have straight or branched chains.
It is often possible to draw more than one structural formula for a given molecular formula,
There is often a straight-chain compound and one or more branched-chain compounds with
the same molecular formula.
For C4H10, there are two possible structural formulae:
Butane Methylpropane
These two compounds are isomers because they have the same molecular formula but
different structural formula.…read more

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Alkane molecules with cyclic structures are called cycloalkanes.
They have the general formula CnH2n.
They have two fewer hydrogen atoms than the corresponding alkane, because there are no
­CH3 groups at the ends of the chain.
This table shows different ways of representing cycloalkanes.
The skeletal formula shows only the shape of the carbon framework.
Each line represents a C-C bond.
The carbon atoms are at the corners.…read more

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Shapes of Alkanes
The best way to show a molecular structure on paper is to use the following:
Represents a bond in the
plan of the paper
Represents a bond in a
direction behind the
plane of the paper
Represents a bond in a
direction in front of the
plane of the paper
The shape of a hydrocarbon is often represented by a skeletal formula:…read more

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What are Alkanes Like?
Whether an alkane is a solid, liquid or gas at room temperature depends on the size of its
The first four members of the series are colourless gases.
Higher members are colourless liquids and the remainder are white waxy solids.
At room temperature and pressure:
C1 - C4 are gases
C5 - C15 are liquids
C16 - are solids
Alkanes mix well with each other, but do not mix with water.
They alkanes and water form two separate layers.…read more

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Chemical Reactions of Alkanes
Alkanes are very unreactive towards many laboratory reagents.
They are unaffected by polar reagents such as acids and alkalis, or oxidising agents such as
potassium manganate.
When they do react, it is usually in the gas phase and energy must be supplied to get the
reaction started.
Oxidation of Alkanes
Alkanes do not react with air at room temperature but, if heated, they burn readily to give
carbon dioxide and water.…read more

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Alkenes have the general formula CnH2n.
They are made out of carbon and hydrogen so they are hydrocarbons.
They have at least one double covalent bond.
They are unsaturated because they can make more bonds with extra atoms in addition
Name Formula Skeletal Formula
Propene CH3-CH=CH2
But-1-ene CH3-CH2-CH=CH2
But-2-ene CH3-CH2-CH=CH2
Pent-1-ene CH3-CH2-CH2-CH=CH2
The first part of the name tells you how many carbon atoms it has.
The second part of the name ­ene tells you it is an alkene.…read more

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Cycloalkenes have 2 less hydrogen atoms than an open-chain alkene.
Properties of Alkenes
The boiling points of alkenes increase as the number of carbon atoms increases.
Ethene, propene and the butenes are gases.
After this, they are liquids and eventually solids.
Shapes of Alkenes
Ethene is a flat molecule with the shape as shown.
The bonds around the C=C group are arranged the same way in
all alkenes.…read more


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