Structural isomerism in the alkanes
3 marks · EasyState the difference between a straight-chain alkane and a branched-chain alkane.
Draw the displayed formula for a branched structural isomer of C5H12.
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(a) A straight-chain alkane has all carbon atoms joined in a continuous chain. A branched-chain alkane has at least one branch off the main chain.
(b) A displayed formula showing a branched isomer of C5H12, e.g. 2-methylbutane or 2,2-dimethylpropane, with all atoms and bonds shown. · must show all C and H atoms correct for the branched isomer, branch clearly shown, no missing or extra atoms
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States structural difference between straight and branched-chain alkane
B2 (b) · 2 marks · Displayed formula for branched C5H12 isomer, with all atoms and bonds correctly shown
Worked solution
a) A straight-chain alkane has all carbons joined in a continuous row, no branches. A branched-chain alkane has at least one carbon atom attached as a side group.
b) Example: 2-methylbutane displayed formula (all C–C and C–H bonds shown, with a 4-carbon chain and a methyl group on carbon 2).