Which of the following compound is assigned the octane number of 100?
Correct answer: D. 2,2,4-trimethylpentane
- A. n-heptane
- B. n-octane
- C. 2,3,3-trimethylpentane
- D. 2,2,4-trimethylpentane
Explanation
The correct answer is 2,2,4-trimethylpentane, also known as isooctane. It is assigned an octane number of 100 because it has excellent knock resistance in engines. This compound serves as a standard reference point in the octane rating scale, indicating that it can withstand high compression without detonating prematurely. In contrast, n-heptane, with an octane number of 0, has very poor resistance to knocking. n-Octane has an even lower resistance, indicated by its negative octane number. 2,3,3-Trimethylpentane, while having a high knock resistance, does not serve as the standard reference and has a different octane rating.
This question appeared on the ETEA MDCAT 2014 paper, which you can sit online with every answer explained.
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About Alkanes
Alkanes are saturated hydrocarbons containing only carbon-carbon and carbon-hydrogen single bonds, with the general formula CnH2n+2 for open chains. Their structure, isomerism, IUPAC nomenclature, physical properties, combustion, free-radical halogenation and conformations are covered, including the difference between substitution in alkanes and addition in unsaturated hydrocarbons.
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