The organic compound used as antiknock agent in petroleum is____________?

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(C₂H₅)₄Pb - In petroleum fuels, knocking is an undesirable phenomenon where fuel-air mixture in an internal combustion engine burns unevenly, causing a sharp metallic sound and reducing engine efficiency. To overcome this problem, antiknock agents are added to fuel to improve its octane rating, ensuring smooth combustion.
The primary organic compound historically used as an antiknock agent is tetraethyl lead (TEL), with the chemical formula (C₂H₅)₄Pb. TEL is an organometallic compound consisting of four ethyl groups bonded to a lead atom. When added to gasoline in small amounts, it slows down the ignition rate of the fuel mixture, preventing premature detonation inside the engine cylinder.
 Other options in the question serve different purposes. TNT (trinitrotoluene) is an explosive and not used in fuels. CH₃MgBr (methylmagnesium bromide) is a Grignard reagent, widely used in organic synthesis but not as a fuel additive. (C₂H₅)₂Hg (diethyl mercury) is a toxic mercury compound with no antiknock application.




Tetraethyl lead became popular in the 1920s and was extensively used for decades in gasoline to enhance performance. However, due to its toxic effects on human health and the environment, the use of leaded gasoline has been phased out in most countries since the late 20th century. Today, safer alternatives like ethanol and other oxygenated additives are used to improve fuel combustion without harmful lead emissions.
Understanding antiknock agents is an important topic in organic chemistry and fuel technology, as it links the chemical structure of organic compounds to their practical applications in the petroleum industry. TEL remains a significant example of how organometallic compounds were used to solve industrial combustion problems before environmental concerns led to cleaner fuel technologies.

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