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The names of simple organic compounds are composed of two parts -
|1 carbon atom :||meth___||19 carbon atoms :||nonadec___|
|2 carbon atoms :||eth___||20 carbon atoms :||eicos___|
|3 carbon atoms :||prop___||21 carbon atoms :||heneicos___|
|4 carbon atoms :||but___||22 carbon atoms :||docos___|
|5 carbon atoms :||pent___||23 carbon atoms :||tricos___|
|6 carbon atoms :||hex___||24 carbon atoms :||tetracos___|
|7 carbon atoms :||hept___||25 carbon atoms :||pentacos___|
|8 carbon atoms :||oct___||26 carbon atoms :||hexacos___|
|9 carbon atoms :||non___||27 carbon atoms :||heptacos___|
|10 carbon atoms :||dec___||28 carbon atoms :||octacos___|
|11 carbon atoms :||undec___||29 carbon atoms :||nonacos___|
|12 carbon atoms :||dodec___||30 carbon atoms :||triacont___|
|13 carbon atoms :||tridec___||31 carbon atoms :||hentriacont___|
|14 carbon atoms :||tetradec___||32 carbon atoms :||dotriacont___|
|15 carbon atoms :||pentadec___||33 carbon atoms :||tritriacont___|
|16 carbon atoms :||hexadec___||34 carbon atoms :||tetratriacont___|
|17 carbon atoms :||heptadec___||35 carbon atoms :||pentatriacont___|
|18 carbon atoms :||octadec___||36 carbon atoms :||hexatriacont___|
With alkanes this suffix is ___ane.
With alkenes this suffix is ___ene.
With haloalkanes the basis for the name is the parent organic group (e.g. alkane, alkene, etc.)
Count the number of carbon atoms from the nearest chain end to where the halogen is attached.
Second comes the prefix based on which halogen element is present,
Simply add the normal unchanged alkane (or alkene) name onto the suffix (see naming alkanes in the alkanes page).
With alcohols this suffix is ___anol.
With aldehydes this suffix is ___anal.
With ketones this suffix is ___anone.
- this depends on the number of carbon atoms in the longest chain
- count from the nearest chain end to the carbonyl carbon atom
- add __anone around the position number at the end of the prefix
Exemplar compounds -
With carboxylic acids this suffix is ___anoic acid.
|ethanoic acid :|
|3-methylpentanoic acid :|
With esters this suffix is ___anoate.
|ethyl ethanoate :|
|1-methylethyl propanoate :|
They are called alkanes as they do not have any carbon-carbon double bonds. The name is based on the alkane with the same number of carbon atoms. Cyclo__ is added as a prefix to the whole name.
They are called alkenes as they have a carbon-carbon double bond. The name is based on the alkene with the same number of carbon atoms. Cyclo__ is added as a prefix to the whole name.
This is also known as branching in a molecule.
When the alkane, or any other organic molecule, is not just a simple straight chain of carbon atoms joined together the names become a little more complex.
The longest connected chain of carbon atoms must be found as before and the alkane (alkene, alcohol, etc.) name generated as usual. For example, with 5 carbon atoms and 12 hydrogen atoms :
|5 carbon atoms long is a pentane||4 carbon atoms long is a butane||3 carbon atoms long is a propane|
Then the name for the pendent group is found, again by counting the number of carbon atoms present, and used as a prefix.
|CH3- group :||methyl___|
|CH3CH2- group :||ethyl___|
|CH3CH2CH2- group :||propyl___|
|CH3CH2CH2CH2- group :||butyl___|
The pendent group is itself prefixed by a number denoting which carbon atom it is attached to, followed by a hyphen.
If there is more than one of the same pendent group then each group is numbered, with a comma used to separate the numbers. The group is also prefixed by di__ to denote two of them, tri__ to denote three of them, tetra__ to denote four of them, penta__ to denote five of them, etc.
Continuing the previous examples :
|No pendent groups = pentane||1 pendent methyl group on the 2nd carbon = 2-methylbutane||2 pendent methyl groups on the 2nd carbon = 2,2-dimethylpropane|
N.B.: The numbers used to indicate the positions of the pendent groups must be the lowest numbers possible, so always check them from both ends of the molecule.
There are a number of different ways of representing an organic molecule, and all of them will probably examined in AS and A2 question papers.
The simplest is a molecular formula, which is simply the number of each type of atom totaled up.
A structural formula separates the atoms into groups, such as CH3 and CH2 parts of a molecule.
A displayed structure shows all the bonds between the atoms, including all the bonds going to hydrogen atoms.
A skeletal structure is similar to the displayed structure, though all the hydrogens are removed, including any bonds to hydrogen atoms, and the labels for carbon atoms are removed as well. Labels for atoms other than carbon are kept (see the nomenclature sections of other homologous series for examples of their skeletal formulae).
e.g. for propane,
|molecular formula :||C3H8|
|structural formula :||CH3CH2CH3|
|displayed formula :|
|skeletal formula :|
and for 3-ethylpentane the skeletal formula would look like this -back to top
|Homologous Series||General||Functional||Exemplar Compound|
Cyclic Esters (Lactones)
written by Dr Richard Clarkson : © Saturday, 1 November 1997
Updated : Monday 22nd October, 2012
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