Year 10 Chemistry, Mr Blaurock – Worksheet 8
1.6. Naming alkane molecules with side chains
Nonane (C9H20) has 35 isomers. And where we could easily name the two butane isomers n-butane and i-butane it is obvious it becomes quite difficult giving each of these 35 isomers its own name.
That is why in 1919 chemists from all around the world founded the „International Union of Pure and Applied Chemistry” (or IUPAC for short) with one of the explicit goals being finding a
internationally unified way to name complex organic molecules (one of the other goals by the way is naming newly discovered elements and assigning element symbols). We already know a part of the IUPAC naming system, or nomenclature: the naming of the first ten n-alkanes!
The first syllable in a hydrocarbons name (Met-, Et-, Prop-, But-, …) stays an indicator of _________
__________________ in the main chain. Also the ending “-ane” still signifies an alkane (general molecular formula: _____________). The new part of the naming system is the naming and numbering of side chains in branching alkanes.
The name of any given alkane can be determined in four easy steps:
1. Determine the longest carbon chain in the molecule.
The number of carbon atoms in the longest chain (or main chain) determines its name and forms the end of the molecules name.
2. Determine the side chains in the molecule and order alphabetically.
3. Side chains are always directly connected to the main chain and their name is also
determined by the number of carbon atoms. Only difference is that their name ends in “-yl”
instead of “-ane” because, compared to an alkane molecule, they are missing a hydrogen atom. The names of the side chains listed before the main chain.
4. Determine number of identical side chains.
If there is more than one, a Greek prefix (di-, tri-, tetra-, penta-, hexa-,…) signals the number.
5. Determine the main chain carbon atoms the side chains are linked to.
The carbon atoms in the main chain are numbered in such a way, that the numbers of the carbon atoms the side chains link to are as small as possible. The numbers are listed in front of the side chains name, if there are several identical side chains, the number for each individual side chain is listed, separated by a colon.
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Year 10 Chemistry, Mr Blaurock – Worksheet 8
Examples
1. Write the condensed molecular formula for the following compounds:
a) 2,2,3,3–Tetramethylpentane b) 2,3–Dimethylbutane
c) 3,4,4,5–Tetramethylheptane d) 3–Ethyl–3,4–dimethylheptane e) 4–Ethyl–2,4–dimethylheptane f) 2,5–Dimethylhexane
g) 3–Ethyl–2–methylpentane h) 2,2,4–Trimethylpentane
2. Name the following compounds according to the IUPAC nomeclature.
a) b) c)
d) e)
f) g)
