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JEE Main · 2021 · 22 Jul 2021 · Shift 2 · General Organic Chemistry

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The number of acyclic structural isomers (including geometrical isomers) for pentene is ______.

Answer: 6

Solution

Pentene is with one double bond and no ring. The unbranched chain gives pent-1-ene and pent-2-ene; in pent-2-ene one doubly bonded carbon carries a methyl and a hydrogen and the other an ethyl and a hydrogen, so it exists as cis and trans forms. The branched skeleton gives 2-methylbut-1-ene, 3-methylbut-1-ene and 2-methylbut-2-ene, and in each of these one doubly bonded carbon carries two identical groups, so none of them shows geometrical isomerism. Counting pent-1-ene, cis-pent-2-ene, trans-pent-2-ene, 2-methylbut-1-ene, 3-methylbut-1-ene and 2-methylbut-2-ene gives 6 acyclic isomers.

JEE Main · 2021 · 22 Jul 2021 · Shift 2 · Integer answer

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