Coding for branched chains
3 marks · NormalThe systematic name of a hydrocarbon is 3-ethyl-2-methylpentane.
State the number of carbon atoms in the longest chain, and give the total number of carbon atoms in the complete molecule.
Show your reasoning.
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
Longest chain = 5 carbons; total carbons = 8
Also accept: Longest chain five carbons; total of eight carbons
Common mistakes: Only counting the side chains but not the main chain; Forgetting to add both the ethyl and methyl group carbons
Show mark scheme and worked solution
Marking points
M1 · 1 mark · States or deduces that the longest chain has 5 carbons (from 'pentane').
M2 · 1 mark · Identifies that there is an ethyl group (2 carbons at position 3) and a methyl group (1 carbon at position 2).
A1 · 1 mark · Correctly calculates the total number of carbon atoms as 8. (follow-through)
Worked solution
The name ends in 'pentane', which means the longest chain has 5 carbons.
There is an ethyl group (CH3CH2–, 2 carbons) at position 3, and a methyl group (CH3–, 1 carbon) at position 2.