roadmap question (NaOC2H3)

[patricklin27]

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^For this reaction, why does this reaction go through E2 instead of SN2? I know OC2H5- is a strong base/strong nucleophile. I always thought a secondary halide and a good leaving group would be a SN2 reaction, not E2.

^and for this reaction, why does this one go through SN2 and not E2? Is it because it is a primary halide?

 

[DrRoyal Pains]

I remember it like this: Primary/methyl halides go SN2, and secondary/tertiary halides go E2. If you notice, in the first picture you have a secondary halide, and in the second picture, you have a primary halide. Hope this helps!

 

[patricklin27]

i believe secondary halides can go through SN2 as well as E2 (if you watched chad's videos). How do you know when SN2 or E2 will occur for secondary halides? I learned that if there is a good leaving group for the secondary halide, it usually goes through SN2. However, that is obviously wrong because of the reaction above.

 

[Ferneezy]

first reaction could go sn2, but if it goes e2 it forms a highly conjugated system, which means good stability juju.

second reaction cannot go e2 as there are no beta protons to extract.