先消去得到丙烯：CH3CHBrCH3+NaOH-醇溶液->CH2=CHCH3+NaBr+H2O和Br2加成：CH2=CHCH3+Br2→CH2BrCHBrCH3再消去：CH2BrCHBrCH3+2NaOH→CH≡CCH3+2NaBr+2H2O和HBr加成：CH≡CCH3+2HBr→CH3CBr2CH3...