Isobutylene

Isobutylene, or 2-methylpropene, is a branched four-carbon alkene with formula C₄H₈. Its terminal carbon–carbon double bond makes it a useful feedstock for polymers and chemical intermediates.

Butyl rubber: A synthetic elastomer made by copolymerizing isobutylene with a small amount of isoprene. Isobutylene supplies most of the polymer chain and gives the rubber its low gas permeability.
Electrophilic addition: A reaction in which an electrophile adds to a carbon–carbon multiple bond, followed by a nucleophile. Isobutylene’s electron-rich double bond commonly undergoes this reaction pattern.
Alkene: An unsaturated hydrocarbon containing at least one carbon–carbon double bond. Isobutylene is a simple, branched member of this hydrocarbon family.
Fluid catalytic cracking: A petroleum-refining process that breaks heavy hydrocarbons into lighter products using a circulating catalyst. Its refinery gas streams contain isobutylene among other light olefins.
1-Butene: A straight-chain four-carbon alkene with its double bond at the end of the carbon chain. It shares formula C₄H₈ with isobutylene but has an unbranched carbon skeleton.
Polyisobutylene: A polymer formed by linking isobutylene molecules into long chains. This direct polymerization route turns the alkene into sealants, lubricants, and fuel additives.
Carbocation: An organic ion in which a carbon atom bears a positive charge. Protonation of isobutylene can form a relatively stable tertiary carbocation intermediate.
Isomerism: The existence of compounds with the same molecular formula but different structures or spatial arrangements. Isobutylene shares formula C₄H₈ with other compounds but has a distinct branched structure.
Steam cracking: A high-temperature process that converts hydrocarbons into smaller molecules, including olefins. Cracking streams can supply isobutylene, though it is mixed with other hydrocarbons.
2-Butene: A four-carbon alkene with an internal double bond, existing as cis and trans geometric isomers. Its internal double bond and straight-chain skeleton contrast with isobutylene’s terminal, branched structure.

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