Coding for branched chains

4 marks · Normal

Study the following table showing the names and structures of several branched alkanes.

Branched Alkane Structures
Name	Longest chain	Side chain(s)	Position(s)
2-methylbutane	butane	methyl	2
3-ethylpentane	pentane	ethyl	3
2,2-dimethylpropane	propane	methyl (x2)	2,2
4-methylhexane	hexane	methyl	4

(a)

Which molecule in the table has two side chains?

[1 mark]

(b)

State the side chain and its position for 3-ethylpentane.

[1 mark]

(c)

For which compound is the main chain the longest?

[1 mark]

(d)

What is the coded name for a side chain containing two carbon atoms?

[1 mark]

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.

Show answer

(a) 2,2-dimethylpropane

(b) ethyl at position 3

(d) ethyl

Common mistakes: missing that 2,2-dimethylpropane has two methyl groups; incorrectly identifying side chain code

Show mark scheme and worked solution

Marking points

B1 (a) · 1 mark · Correctly identifies the molecule with two side chains as 2,2-dimethylpropane.

B1 (b) · 1 mark · States the side chain as 'ethyl' at position 3 for 3-ethylpentane.

B1 (c) · 1 mark · Identifies 4-methylhexane as the compound with the longest main chain ('hexane').

B1 (d) · 1 mark · Gives the coded name 'ethyl' for a side chain containing two carbons.

Worked solution

a) 2,2-dimethylpropane has two methyl side chains.

b) 3-ethylpentane has an ethyl side chain at position 3.

c) 4-methylhexane ('hexane' is the main chain, 6 carbons, the longest here).

d) The coded name for a side chain with two carbons is 'ethyl'.