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Questions & Answers

A mixture of isomeric alkenes is produced when pentan-2-ol is dehydrated in the presence of hot concentrated sulfuric acid. Pent-1-ene is one of the isomers produced. Name and outline a mechanism for the reaction producing pent-1-ene.

The Dehydration/Elimination reactions of Alcohols are catalysed by Sulfuric Acid, initiated by attack of nucleophile so called Nucleophilic Elimination Reaction. In the reaction mechanism that follows:

  1. The lone pair on the oxygen atom in the hydroxyl group of alcohol attacks as a nucleophile on hydrogen of Sulfuric Acid.

  2. This results in Oxygen forming three bonds, making it unstable. The OH2+ group leaves as the bond breaks heterolytically in favour of oxygen. 

  3. The carbocation formed is stabilized as the adjacent carbon loses its hydrogen to HSO4- group, and forms another bond with carbon having positive charge. The resulting structure is alkene.

 In the case of pentan-2-ol, the bond can form between (terminal and 2’carbon) or ( 2’and 3’carbon). The former results in formation of 1-pentene.

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