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Sn2/E2 exercise correction
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xshadow:
Hi, can you help me with this exercise:
https://i.imgur.com/sqB2YQV.jpg
Are the products written corrected?
In the first one can an E2 occours forming ALSO the secondary product HC=C=H2??
Because I have a 1° allylic halide : its stability is similar to a secondary alkyl halide...and in 2° alkyl halide usually E2 and Sn2 are in competition (with strong base/nucleohpilic,of course)
Thanks!!
sharbeldam:
following
kriggy:
You are likely going to get more products, especially in the second case, due to the Sn1´ or Sn2´ substitutions. Sn reactions on secondary halides can go both mechanisms and allylic halides make it even more complex.
https://en.wikipedia.org/wiki/Allylic_rearrangement
for more information
xshadow:
Hi
And what about elimination?
Can E2 occour in a secondary allylic halides? (I 'll get a conjugated diene)
In the second molecule can I get a mixture of E2 and Sn2 products? (Sn1/E1 product low because I'm using a strong base and nucleophile)
Thanks
hollytara:
There are two important variables that aren't given: temperature and solvent.
The first reaction - 3-chloropropene or allyl chloride - is only going to react by SN2, unless very high temperatures are used. The allene product is high energy and requires fairly severe conditions.
The second reaction 3-chloro-1-butene is trickier. If it is set up for SN2 (polar aprotic solvent, low T) you will only get the 3-ethoxy-1-butene. If you try for SN1 (low concentration of ethoxide, refluxing ethanol) you will get the SN1 products - 3-ethoxy-1-butene and 1-ethoxy-2-butene (probably as a mixture of E and Z) with some elimination product (1,3-butadiene). If you go for E2 conditions (high concentration of ethoxide, refluxing ethanol) you will get essentially only the 1,3-butadiene product.
A nice summary of this can be found in the "MAximum Success, Minimum Effort" book by Fredlos
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