Introduction to Organic Chemistry
7 marks · HardThis question involves both the type of compound and the naming of branched alkanes, including side chain positions.
Name the type of compound shown by the ending 'ane' in '2-methylpropane'. State what this ending tells you about the bonds between the carbon atoms.
Give the IUPAC name for the following structure, showing all working:
Step 1: Identify the longest chain.
Step 2: Determine the position and type of side chain(s).
Step 3: Write the systematic name.
Describe how the rules for naming branched alkanes make sure that side chain positions are coded clearly.
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) 'Ane' shows the compound is an alkane, meaning it has only single bonds between carbon atoms.
(b) Longest chain is propane (3 carbons: B–C–D). There is a methyl group attached at carbon 2 (from C–E). Name: 2-methylpropane. · must show identifying main chain, correct side chain position, correct systematic name
(c) Chains are numbered from the end that gives the branch the lowest possible position number, so side chain positions are always unambiguous.
Must show: Identification of longest chain, Position/type of branch
Common mistakes: Incorrectly numbering the chain, leading to wrong branch position; Omitting the side chain name or misnaming the compound
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Correctly names 'ane' as showing alkane.
B2 (a) · 1 mark · States that 'ane' means all single bonds between carbons.
M1 (b) · 1 mark · Identifies longest chain (propane, 3 carbons).
M2 (b) · 1 mark · Identifies methyl branch at carbon 2.
A1 (b) · 1 mark · Names compound as 2-methylpropane.
C1 (b) · 1 mark · Clearly lays out naming steps.
C2 (c) · 1 mark · Explains how number assignment ensures clear branch position coding.
Worked solution
a) 'Ane' means the compound is an alkane (a saturated hydrocarbon with only single bonds between carbon atoms).
b) Working:
- Step 1: The longest continuous chain is three carbons (B–C–D); this is propane.
- Step 2: There is a methyl side group (CH3) attached at carbon 2 (from C–E).
- Step 3: The name is 2-methylpropane.
c) To make branch positions clear, the chain is numbered from the end that gives the lowest possible number(s) to the side branch(es), ensuring the name uniquely identifies the structure.