Coding for branched chains
4 marks · NormalA hydrocarbon molecule contains six carbon atoms in its longest chain and a methyl group as a side chain.
What is the name of the six-carbon main chain?
If the methyl group is attached to carbon atom 2 (when numbered from the end closest to the side chain), give the IUPAC name of the compound.
Explain why it is important to number from the end of the chain closest to the side chain.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) hexane
(b) 2-methylhexane
(c) To ensure the smallest number is given to the side chain's position, following IUPAC rules.
Also accept: 2-methylhexane
Common mistakes: wrongly numbering chain; missing the '2-' in IUPAC name
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correctly identifies the main chain as 'hexane'.
M1 (b) · 1 mark · Gives the name in correct IUPAC format: chain position first, then side chain, then main chain.
A1 (b) · 1 mark · Gives the correct position (2-methylhexane).
B1 (c) · 1 mark · Explains that numbering from the nearest end gives the side chain the smallest possible number, per IUPAC rules.
Worked solution
a) The six-carbon main chain is called 'hexane'.
b) The methyl group is attached at position 2, so the IUPAC name is 2-methylhexane.
c) Numbering from the end closest to the side chain ensures the smallest possible number is used, as required by IUPAC naming conventions.