Question

Which one is true for the octane number of the following organic compounds?
A.Aromatic Compound > aliphatic compound
B.Aromatic compound < aliphatic compound
C.Aromatic compound = aliphatic compound
D.None of the above

Answer 1

Hint:The Octane number of an organic compound is defined as the measure of the ability of the fuel to resist knocking when ignited in a mixture with air in the cylinder of an internal –combustion engine. Octane rating decreases with the increase in the length of the carbon chain.

Complete step by step solution:
 The anti-knock number is decided by comparing under standard conditions, the knock intensity of the fuel with that of blends of two reference fuels, isooctane that resists knocking and heptane that knocks readily. The octane number is the percentage by volume of isooctane in the isooctane-heptane mixture that matches the fuel being tested in a standard test engine.
It has been seen that the octane rating decreases with the increase in the length of the carbon chain, it increases with the increase in carbon-chain branching. Octane rating increases for aromatic compounds, with the same number of carbon atoms.
So from the above points it is clear that the octane number of Aromatic Compound > aliphatic compound.

So, the correct answer is option A.

Note:
The octane number is a measure of the performance of an engine or aviation gasoline. The higher the octane number the more compression the fuel can withstand before detonating. In broader terms, fuels with a higher octane rating are used in high performance gasoline engines that require high compression ratios.