Which of the following will undergo hydrolysis by \(\mathrm{S}_{\mathrm{N}} 1\) mechanism most readily? 1

In all four compounds, the leaving group is Chlorine.

Higher carbocation stability will favor the formation of the intermediate, making the reaction more likely to occur via an SN1 mechanism. 1) Chlorobenzene: The unsubstituted benzene ring is neither electron-withdrawing nor electron-donating. 2) p-Nitrochlorobenzene: The nitro group (-NO2) at the para position has a strong electron-withdrawing effect which can stabilize the carbocation formed after chlorine leaves. 3) o-Nitrochlorobenzene: The nitro group (-NO2) at the ortho position is also strongly electron-withdrawing, potentially stabilizing the carbocation. However, the steric hindrance in the ortho position could negatively impact the reaction. 4) \(\mathrm{p}\text{-}\mathrm{Methoxy}\text{-}\mathrm{chlorobenzene}\): The methoxy group (-OCH3) is electron-donating which could destabilize the carbocation.

Considering the effects of the substituents on carbocation stability and steric hindrance, we can rank the compounds in terms of their reactivity via an SN1 mechanism. The order of hydrolysis reactivity via SN1 mechanism is: \(\mathrm{p}\text{-}\mathrm{Nitrochlorobenzene} \;>\; \mathrm{o}\text{-}\mathrm{Nitrochlorobenzene} \;>\; \mathrm{Chlorobenzene} \;>\; \mathrm{p}\text{-}\mathrm{Methoxy}\text{-}\mathrm{chlorobenzene}\) Therefore, the compound that will undergo hydrolysis by the SN1 mechanism most readily is p-Nitrochlorobenzene (option 2).