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Topic 7 ­ Basic Concepts
Revision Notes
1) Formulae
Be able to recognise and use the different ways of showing organic compounds.
Molecular formula is the actual number of atoms of each element in a molecule
e.g. C2H6O for ethanol
Empirical formula is the simplest whole number ratio of the atoms of each
element in a molecule e.g. CH2 for ethene (from molecular formula C2H4 2)
General formula is the simplest algebraic formula for a member of a homologous
series e.g. CnH2n+2 for alkanes
Structural formula is the minimum detail that shows the arrangement of the
atoms in a molecule e.g. CH3CH2OH for ethanol
Displayed formula shows the relative positioning of atoms and the bonds
between them e.g. for ethanol:
All bonds should be shown. Do not put ­OH for the alcohol group
Skeletal formula shows just the carbon skeleton and functional groups e.g. for
ethanol (see also Appendix 1)
2) Functional groups and naming organic compounds
Be able to recognise and use the following terms.
A homologous series is a series of organic compounds having the same
functional group with successive members differing by CH2
Alkanes, alkenes, alcohols and halogenoalkanes are all homologous series
A functional group is a group of atoms responsible for the characteristic
reactions of a compound e.g. C=C for alkenes and ­OH for alcohols
The rules for naming organic compounds are as follows.
1) The functional group gives the ending of the name e.g. ­ol for an alcohol
2) The number of carbons gives the first part of the name e.g. prop or propan for
3 carbons
3) Number the carbon chain to give the functional group carbon the lowest number
4) Any side chains (branches) or halogens go at the front of the name with commas
between numbers and dashes between numbers and words e.g.

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With more than 1 side chain or halogen, use alphabetical order e.g.
3) Structural isomers
Structural isomers have the same molecular formula but different structural formulae
e.g. the molecular formula C4H19Br can produce four different structures
Differences between structural isomers arise from the position of the functional
group and/or the arrangement of the carbon chain e.g.…read more

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In the following reaction, 2.18g of bromoethane produce 0.75g of ethanol. Calculate the
percentage yield.
Moles of reactant (bromoethane) = mass/molar mass
= 2.18/109
= 0.020 mol
Possible moles of ethanol = 0.020 mol (from equation)
Actual moles of ethanol = 0.75/46.0
= 0.0163 mol
Percentage yield = 0.0163/0.…read more

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More on naming organic compounds
This section covers naming compounds with more than one alkene or alcohol
functional group
a) Dienes
Compounds containing two alkene groups are called dienes e.g.
The name of this compound is buta1,3diene
b) Diols and triols
Compounds containing two alcohol groups are called diols while three ­OH groups
makes a triol e.g.…read more

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Appendix 1 Skeletal Formulae
Skeletal formulae show carboncarbon bonds and functional groups
Alkane e.g. hexane
Alkene e.g. hex3ene
Alcohol e.g. ethanol
Halogenoalkane e.g. 2chloro2fluoropentane
Aldehyde e.g. butanal
Ketone e.g. propanone
Carboxylic acid e.g. 3methylbutanoic acid
Ester e.g. methyl propanoate
Amine e.g.…read more

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Topic 8a ­ Alkanes
Revision Notes
1) General
Alkanes are saturated hydrocarbons with general formula CnH2n+2
Saturated = only single CC bonds
Hydrocarbon = contains C and H only
CH bonds are nonpolar (C and H have similar electronegativities) so:
o The only intermolecular forces in alkanes are Van der Waal's forces
o Alkanes do not attract charged species (nucleophiles and electrophiles)
In alkanes, the bonds round each carbon are tetrahedral in shape.…read more

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The mechanism here is called radical substitution
Initiation step e.g. Br2 2Br
Propagation e.g. CH4 + Br CH3 + HBr } as a
CH3 + Br2 CH3Br + Br } pair
Termination step e.g. 2 CH3 CH3CH3
Further substitution can occur with more H's being replaced by Br's
CH3Br + Br2 CH2Br2 + HBr etc
The reaction produces a mixture of products (CH3Br, CH2Br2, CHBr3 and CBr4).…read more

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Topic 8b ­ Fuels
Revision Notes
1) Fractional Distillation
Crude oil is a mixture of many compounds, most of which are alkanes.
Crude oil is separated into fractions, many of which can be used directly as fuels.
The separation process is called fractional distillation.…read more

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Isomerisation increases the octane number of the hydrocarbon
It needs a catalyst and heat
c) Reforming
Reforming turns straight chain alkanes into cyclic alkanes and arenes (and
hydrogen) e.g.
C6H14 C6H12 + H2
Hexane cyclohexane
C6H14 C6H6 + 4H2
Hexane benzene
Arenes contain a benzene ring (see A2 Topic 1). Benzene can be represented
in several ways.…read more

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Unsaturated = contain a double C=C bond
Hydrocarbon = contains C and H only
2) Bonding in Alkenes
o The carbons at either end of the double bond and the 4 atoms they are bonded to
are all in a plane (flat). These 6 atoms are joined by single bonds
o The bonds around each C in the C=C bond are trigonal planar in shape.…read more


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