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Question
Predict the major product of acid catalysed dehydration of butan-1-ol.
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Solution 1
Acid catalysed dehydration of butan-1-ol produces but-2-ene as the main product and but-1-ene as the secondary product. This is because dehydration of alcohols takes place through carbocation intermediates. Again, butan-1-ol being a 1° alcohol, on protonation and elimination of H2O, first gives a 1° carbocation (I), which being less stable rearranges to form more stable 2° carbocation (II), then it removes a proton in two different ways to form butan-2-ene or but-1-ene. Since butan-2-ene is more stable, it is the main product according to Saytzeff’s rule.

Solution 2
\[\ce{CH3 - CH2 - CH2 - CH2 - OH ->[H+/\Delta] \underset{But-2-ene}{CH3 - CH = CH - CH3}}\]
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