The Zaitsev rule predicts that pent-2-ene is the major product in the dehydrohalogenation of 2-bromopentane, as it has a greater number of alkyl groups attached to the doubly bonded carbon atoms compared to other potential products.
Provide an example illustrating the application of the Zaitsev rule in dehydrohalogenation, and what is the major product formed from 2-bromopentane?
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Applying the Zaitsev rule to the dehydrohalogenation of 2-bromopentane (CH₃CH₂CH₂CH₂CH₂Br) yields two potential products: 1-pentene and 2-pentene. The Zaitsev rule predicts that the major product will be the more substituted alkene, which is 2-pentene. This preference arises because the double bond in 2-pentene is located at the more substituted (secondary) carbon, providing greater stability due to hyperconjugation and resonance effects. Consequently, the Zaitsev rule guides the regioselectivity of the reaction, favoring the formation of the more stable and substituted alkene in the dehydrohalogenation of 2-bromopentane.