thehipster

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E2 Elimination Question. This is probably a simple question but does the use of ANY strong base with a primary alkyl halide make an E2 reaction or is it only strong, bulky bases, like LDA or t-butoxide?

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Yellow Snow

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Someone on here the other day was saying that using KOH would do E2 on a primary alkyl halide. I'd like to see some confirmation on that.
 

keibee82

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Yellow Snow said:
Someone on here the other day was saying that using KOH would do E2 on a primary alkyl halide. I'd like to see some confirmation on that.

Yes, strong base means either E2 or Sn2 depending on substrates. KOH
with primary alkyl halide is possible with E2 and you also get Sn2. Primary
alkyl halides are great substrate for Sn2 reaction because they are
unhindered.
 
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cryptozoologist

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i'm taking ochem this summer and we just finished this section. E2 is only possible on 1prime c with strong bulky base. regular strong bases only work with 2 and 3 prime cs.

if it's just a strong base and primary c, then it's SN2.
 
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thehipster

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I keep hearing mixed answers like this which is keeping me confused
 

DMD-2-B

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thehipster said:
I keep hearing mixed answers like this which is keeping me confused
Just go to google and type in "E2 Organic Chem." There are some pretty neat tables that summarize all this confusion.
 

Uracil

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cryptozoologist said:
i'm taking ochem this summer and we just finished this section. E2 is only possible on 1prime c with strong bulky base. regular strong bases only work with 2 and 3 prime cs.

if it's just a strong base and primary c, then it's SN2.
That's correct people!
 

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For primary, secondary or tertiary carbons, E2 can still happen with a strong bulky base. keep in mind, lots of times these rxn occur simultaneously, for example a primary carbon will favor SN2, however, that does NOT mean E2 will not occur. it simply means if you going for the SN2 product, it would be your facor to use primary carbon with a strong nucleophile. just as note, there is minor difference between a strong base and strong nucleophile when talkin about substituion vs elimination. a strong nucleophile will want to donates it electrons and attacks the carbon forcing the leavin group off (sn2). a good base draws also has electrons to donate, but it will tear off a proton (E2). of course, a good base can also be a good nucleophile, that is why we use bases like tert-butoxide, which does not attach onto the akyl group bc of steric hindrance.
 

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cryptozoologist said:
i'm taking ochem this summer and we just finished this section. E2 is only possible on 1prime c with strong bulky base. regular strong bases only work with 2 and 3 prime cs.

if it's just a strong base and primary c, then it's SN2.
Not entirely true, strong bases do not support sn2, they support e2. sn2 is supported by a strong nucleophile (weak lewis base).
 

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Yellow Snow said:
Someone on here the other day was saying that using KOH would do E2 on a primary alkyl halide. I'd like to see some confirmation on that.
KOH is both a strong nucleophile as well as a good base. both rxn will take place w/o further conditional discrimination. for example, if heat was added, then e2 reaction will predominate. otherwise, i believe sn2 will predominate.
 
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