Mechanism of Dehydration, Methanol & Ethanol

Hint: In phenoxide ion resonance takes place

The structure of ions of ethyl alcohol and phenol are as follows:

CH₃CH₂O^– and  

The ion of phenol which is known as phenoxide ion is resonance stabilized. In phenoxide ion, delocalisation of π-electrons takes place.
But in ethoxide ion it doesnot happen.

Hence, option one is the correct answer.

HINT: Here stability of carbocation is checked. The compound gives more stable carbocation is more reactive.

Dehydration of alcohols involves the formation of a carbocation intermediate. The reaction follows E1 mechanism. The more the stability of carbocation, the higher is the ease of dehydration. The order of stability of carbocation, given by the given compounds, is. Thus, the compound given in the option readily undergoes dehydration.

Hint: In toluene, if the electron-donating group is attached at ortho or para position then the reactivity of toluene increases.

As the electron-donating groups are attached at the ortho and para position of toluene, the electron density of toluene increases. If an electron-withdrawing group is present then the electron density of toluene decreases and the reactivity of toluene decreases.

In o-cresol, the OH group is attached which increases the electron density of the benzene ring and the reactivity of o-cresol

increases toward electrophilic aromatic substitution reaction.

Hint: $SN_1$ reaction mechanism depends on stability of carbocation.

Explanation:
${\mathrm{CH}}_3-\underset{}{\overset{}{}}\underset{\left|}{\overset{\right|}{\mathrm{C}}}{\mathrm{CH}}_3{\mathrm{CH}}_3-\mathrm{O}-{\mathrm{CH}}_3+\mathrm{HI}\to {\mathrm{CH}}_3-\underset{}{\overset{}{}}\underset{\left|}{\overset{\right|}{\mathrm{C}}}{\mathrm{CH}}_3{\mathrm{CH}}_3-\mathrm{I}$ $+$ $\mathrm{HO}-{\mathrm{CH}}_3$