When 2-bromobutane is heated with alcoholic potassium hydroxide (), what is the major organic alkene product according to Saytzeff's rule?
Answer and explanation
Correct answer: D. But-2-ene
- Step 1: Alcoholic promotes base-induced dehydrohalogenation of alkyl halides.
- Step 2: Saytzeff's (Zaitsev's) rule states that dehydrohalogenation of an alkyl halide yields predominantly the more substituted, more highly alkylated alkene.
- Step 3: Elimination of from the C3 methylene carbon yields but-2-ene (a disubstituted alkene with hyperconjugative -hydrogens), which is formed in yield compared to but-1-ene (monosubstituted, yield).
Answer
But-2-ene.
Why not the others: But-1-ene is the minor Hofmann elimination product; 2-Methylpropene has a branched carbon skeleton not present in 2-bromobutane; Butan-2-ol is the substitution product formed with aqueous , not alcoholic.
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