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(A) The dehydration of alcohols in the presence of $H_3PO_4$ proceeds via the formation of a carbocation intermediate. The rate of reaction depends on

Vedclass · Accepted Answer

$II > III > I$

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(A) The dehydration of alcohols in the presence of $H_3PO_4$ proceeds via the formation of a carbocation intermediate. The rate of reaction depends on the stability of the carbocation formed.$I$: Phenol (or cyclohexadienol derivative) forms a highly stable aromatic carbocation (benzene ring system).$II$: Cyclohexadienol forms a conjugated diene system upon dehydration.$III$: Cyclohexenol forms a simple alkene.Comparing the stability of the carbocations formed:$1$. Compound $II$ (cyclohexa$-1,4-$dien$-1-$ol) leads to the formation of benzene,which is highly stable due to aromaticity.$2$. Compound $III$ (cyclohex$-2-$en$-1-$ol) leads to the formation of cyclohexadiene.$3$. Compound $I$ (phenol) is not an alcohol in the aliphatic sense and does not undergo dehydration to an alkene under these conditions; however,based on the provided structures,$II$ is the most reactive due to the formation of aromatic benzene,followed by $III$,and $I$ is the least reactive.Thus,the correct order of reactivity is $II > III > I$.

The correct order of decreasing reactivity towards $H_3PO_4$ for the following compounds is:

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