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Why are branched hydrocarbons useful in gasoline manufacture?

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Two diagrams show the three-dimensional structure of a methane molecule: panel A uses a ball-and-stick model with a central carbon atom connected to four hydrogen atoms in a tetrahedral arrangement, while panel B illustrates the bond angle of 109.5 degrees and bond length of 1.09 angstroms between carbon and hydrogen atoms. — isomerism Tetrahedral geometry of methane: (A) stick-and-ball model and (B) diagram showing bond angles and distances. (Plain bonds represent bonds in the plane of the image; wedge and dashed bonds represent those directed toward and away from the viewer, respectively.)

Branched-chain hydrocarbons are highly valued in the manufacture of gasoline because they possess a significantly higher octane number than their straight-chain isomers.12

In the context of internal-combustion engines, the octane number serves as a measure of a fuel's ability to resist knocking—a phenomenon where fuel vapor combusts too rapidly, reducing engine efficiency. Because branched-chain hydrocarbons are more effective at resisting this premature ignition, they are considered superior motor fuels.3412

To increase the supply of these desirable components, refineries utilize a process called isomerization. This chemical process converts lower-octane, straight-chain hydrocarbons into their corresponding branched-chain isomers. This transformation is a critical step in reforming and other refining operations designed to improve the quality of gasoline.145