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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 ($S_N1$ or $S_N2$))? Explain in as much detail as possible.

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

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


(As requested, I have tried to suggest those reactions)

I suggest if the first reaction will produce methanol and chloride: $$\ce {CH3Cl + OH- -> CH3OH + Cl-}$$ and it is a $S_N2$ reaction, because $\ce {OH-}$ attacking from behind and make $\ce {Cl}$ leave the chloromethane. It is $\ce {Cl-}$ because it brings one electron from the carbon atom.

Then I suggest the second reaction is a $S_N1$ reaction because there are some barrier behind the $\ce {CCl}$ (the barrier is $\ce {(CH3)3}$). But I don't know the product.

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  • $\begingroup$ Please see our homework policy. I'll reopen the question once you explain what you have tried and which concept you're getting stuck on :) $\endgroup$ – ManishEarth Feb 9 '13 at 9:45
  • $\begingroup$ @Manishearth I have tried to suggest. Is it decent to reopen my question? $\endgroup$ – lambda23 Feb 9 '13 at 16:04
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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 $S_N1$ or $S_N2$, we must look at the mechanism of each:

$S_N1$

enter image description here

$S_N2$

enter image description here

Wikipedia:Nucleophilic_Substitution

So we can see that in an $S_N1$ reaction, a stable carbocation intermediate must be formed, while in an $S_N2$ 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 $S_N1$, if the carbocation is relatively unstable, the reaction will likely be $S_N2$.

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 $S_N2$ 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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