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Question
What is dehydrohalogenation? State the rule for the formation of the preferred product of dehydrohalogenation.
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Solution
- Dehydrohalogenation reaction: When an alkyl halide having at least one β-hydrogen is boiled with an alcoholic solution of potassium hydroxide (KOH), it undergoes elimination of hydrogen atom from β-carbon and halogen atom from α-carbon resulting in the formation of an alkene. As hydrogen and halogen are removed in this reaction, it is termed a dehydrohalogenation reaction.
- Saytzeff’s rule:
Statement - “In dehydrohalogenation reaction, the preferred product is that alkene which has a greater number of alkyl groups attached to doubly bonded carbon atoms.”
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\[\begin{array}{cc}\ce{CH3\phantom{................}}\\
|\phantom{...................}\\
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|\phantom{...................}\\
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\[\begin{array}{cc}
\ce{CH3}\phantom{.................}\\
|\phantom{...................}\\
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\[\begin{array}{cc}
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