The formation of branched-chain alkanes, or iso-alkanes, leads to the production of gasoline with high octane numbers.This is the fundamental reason why catalytic cracking has replaced thermal cracking as the central process in a refinery geared to maximize gasoline production.A high octane number of gasoline is needed for current spark-ignition engines to run at high compression ratios without knocking.
High compression ratios in spark-ignition engines translate to high power and high efficiency. Carbocations are the positively charged ions made from hydrocarbons. Figure 7.1 shows that removing a hydride ion (H -, a hydrogen atom with an additional electron) from an alkane (e.g., methane) produces carbenium ions (path 1a). The resulting ion C H 5 is called methanium. Carbenium ions used to be called carbonium ions in some sources, including your textbook 2. All references to carbonium ions in Section 6.3 Cracking Reactions in the textbook should be corrected as carbenium ions. Please send comments or suggestions on accessibility to the site editor. The site editor may also be contacted with questions or comments about this Open Educational Resource.
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