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My teacher gave me the following question:

What are the possible products of these reactions? Then, what is the mechanism of those reaction (elimination (E1 or E2) or subtitution (SN1 or SN2)? Explain in as much detail as possible.

$$\ce {CH3Cl + OH- ->} ?$$

$$\ce {(CH3)3CCl + OH- ->}?$$

I suggest that the first reaction will produce methanol and chloride: $$\ce {CH3Cl + OH- -> CH3OH + Cl-}$$ and it is a SN2 reaction, because $\ce{OH-}$ attacking from behind and this makes $\ce{Cl}$ leave the chloromethane. It becomes $\ce{Cl-}$ because it brings one electron from the carbon atom.

Then I suggest the second reaction is a SN1 reaction because there are some barriers behind the $\ce{C-Cl}$ (the barrier is $\ce {(CH3)3}$). But I don't know the product that can be formed.

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You are on the right track with the hydroxide substituting the chloride, so you can predict the alcohol product in each reaction. In order to determine whether the reactions will be SN1 or SN2, we must look at the mechanism of each reaction:

SN1

enter image description here

SN2

enter image description here

Wikipedia:Nucleophilic_Substitution

So we can see that in an SN1 reaction, a stable carbocation intermediate must be formed, while in an SN2 reaction there is no intermediate. We can determine the stability of our carbocation intermediate by looking at the following stability diagram:

enter image description here

Wikipedia:Carbocation

From the diagram, you can see that carbocation stability increases with the number of alkyl groups attached to the ionized carbon. If the carbocation is relatively stable, the reaction will likely be SN1, if the carbocation is relatively unstable, the reaction will likely be SN2.

Another important idea, which you have mentioned, is that a central carbon surrounded by bulky groups will be more difficult to attack due to steric hindrance (thus not likely an SN2 reaction), and becomes more easily attacked when dissociated to a carbocation.

You can use these concepts to find/explain the answers to your question.

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