Couple Destroyer Road Map Questions

[patricklin27]

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1.

im assuming these two reactions are similar but i dont get why they form an alkene and on the less substituent carbon.



2.

What is this reaction called? Why does it form a triple bond?




3.

CN- is a strong nucleophile but weak base. This means it has to go through SN2. However, this is a tertiary carbon so no rxn would happen. Why would this be Elimination reaction?

Thanks.

 

[free99]

Potassium tert butoxide is a bulky base and will preferentially eliminate at the less substituted carbon due to steric hindrance. The second reaction does form a more substituted Allene as the product.

I think 2 is just a double elimination. 3 is an e2 rxn because it is a 3° halide, which sn2 rxns do not participate in.

 

[patricklin27]

CN- is a strong nucleophile and weak base. Since CN- is a weak base, I thought it wouldnt go through E2?

 

[DenTony11235]

CN- is a strong nucleophile and weak base. Since CN- is a weak base, I thought it wouldnt go through E2?

The trick is the little triangle. It means heat is added. Heat favors elimination reactions. Also, SN2 doesn't work with tertiary products.

 

[biomolecmed]

Yes CN is a weak base, however remember, you cannotmdo sn2 on the tertiary carbocation, elimination however will work much better because of a stable intermediate that is formed.