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Karnataka Board PUCPUC Science 2nd PUC Class 12

Predict the major product of acid catalysed dehydration of butan-1-ol.

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Question

Predict the major product of acid catalysed dehydration of butan-1-ol.

Chemical Equations/Structures
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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.

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Solution 2

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

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Chapter 7: Alcohols, Phenols and Ethers - Intext Questions [Page 213]

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NCERT Chemistry Part 1 and 2 [English] Class 12
Chapter 7 Alcohols, Phenols and Ethers
Intext Questions | Q 7.7 (ii) | Page 213

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