Consider the following species: 1. RCHCH3 2 . RCH2CH2 3 . RCH2CH2OH2 In the dehydration

step 1 Consider the following species. In the dehydration of primary alcohols, the correct sequence of

Consider the following species: 1. RCHCH3 2 . RCH2CH2 ...

Consider the following species: 1. $\mathrm{RCHCH}_{3}$ $\begin{array}{ll}2 . \mathrm{RCH}_{2} \mathrm{CH}_{2} & 3 . \mathrm{RCH}_{2} \mathrm{CH}_{2} \mathrm{OH}_{2}\end{array}$ In the dehydration of primary alcohols, the correct sequence of formation of the species involved is (a) $1,2,3$ (b) $1,3,2$ (c) $3,2,1$ (d) $2,1,3$

Consider the following species:
1. $\mathrm{RCHCH}_{3}$
$\begin{array}{ll}2 . \mathrm{RCH}_{2} \mathrm{CH}_{2} & 3 . \mathrm{RCH}_{2} \mathrm{CH}_{2} \mathrm{OH}_{2}\end{array}$
In the dehydration of primary alcohols, the correct sequence of formation of the species involved is
(a) $1,2,3$
(b) $1,3,2$
(c) $3,2,1$
(d) $2,1,3$

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Key Concepts

Protonation of Alcohol

In acid-catalyzed dehydration reactions, the reaction is initiated by protonation of the alcohol’s hydroxyl group. This step transforms the poor leaving group (OH) into a better leaving group (water) by forming an oxonium ion, thereby facilitating the subsequent elimination process.

Carbocation Formation

Following protonation, the departure of water results in the formation of a carbocation intermediate. Carbocation formation is a key step in the E1 mechanism; however, in the case of primary carbocations they are typically high in energy and thus prone to rearrangements, which drives the reaction toward more stable intermediates.

Carbocation Rearrangement

Primary carbocations can rearrange via hydride shifts or alkyl shifts to form more stable secondary or tertiary carbocations. This rearrangement is pivotal because it allows the reaction to proceed through a lower energy pathway, ensuring that the intermediate is sufficiently stable to undergo the final elimination step.

Elimination Reaction

The final step in the dehydration process is the elimination of a proton from a carbon adjacent to the carbocation, leading to the formation of a carbon–carbon double bond (alkene). This deprotonation completes the E1 mechanism by converting the rearranged carbocation into the final alkene product.

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