During the acid-catalyzed dehydration of $2_{\text{-}}\text{butanol}$, which alkene is the major product?

• A. $\text{cis}-2-\text{butene}$
• B. $1-\text{butene}$
• C. $\text{methylpropene}$
• D. $2-\text{butene}$

Answer: (D)

Verified step by step guidance

1. Identify the structure of 2-butanol: it is a four-carbon chain with an -OH group attached to the second carbon.
2. Understand that acid-catalyzed dehydration involves protonation of the hydroxyl group to form a good leaving group (water), followed by loss of water to generate a carbocation intermediate.
3. Determine the most stable carbocation formed after the loss of water; in this case, the carbocation will be on the second carbon, which is a secondary carbocation and relatively stable.
4. Apply Zaitsev's rule, which states that the more substituted alkene will be the major product because it is more stable due to hyperconjugation and alkyl group electron-donating effects.
5. Draw all possible alkenes formed by elimination and identify the most substituted alkene, which is 2-butene (both cis and trans isomers), as the major product rather than 1-butene or methylpropene.