Naming organic compounds
3 marks · NormalExplain how the name '2-butene' describes the structure of the molecule, according to IUPAC rules.
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Common mistakes: Misidentifying number of carbons; '2' means number of branches; 'ene' means single bond
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Marking points
M1 · 1 mark · Explains 'but-' prefix means 4 carbon atoms in the longest chain.
M2 · 1 mark · Explains '-ene' ending means the molecule has a carbon–carbon double bond (alkene).
M3 · 1 mark · States the '2-' tells you the position of the double bond is between carbon 2 and 3 in the chain.
Worked solution
‘But-’ means the compound has 4 carbon atoms in a chain. The ending ‘-ene’ shows it is an alkene with a carbon–carbon double bond. The number ‘2-’ indicates the double bond starts at the second carbon, i.e., it is between carbon 2 and carbon 3.