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uchicago2012
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Homework Statement
Hello,
We were supposed to fill in the missing products or reagents (I indicated which ones on the paper) but out of 40 points, I got 13. So now I'm a bit worried. I tried to redo it, could someone look it over? (see attached jpg)
The Attempt at a Solution
My reasoning is:
a) Strong base, good nucleophile, secondary alkyl halide, polar protic solvent. So I think it will be E2/Sn2, despite the polar protic solvent, and I think E2 will dominate because I think EtO- is a stronger base than a nucleophile
b) I'm not really sure about this one, because for my first answer I put HBr + heat but I only got 3 points out of 5 for that. I don't understand why that would be a bad answer? But so I tried PBr3 because I know it can brominate things as well, but I honestly don't understand the difference. Both compounds make the OH group into a good leaving group and then brominate it. Did he perhaps take off for the heat? I know heat makes elimination more likely, so maybe that was the issue.
c) It looks like OEt was added and my book says R-OH can open an epoxide ring as long as an acid is present, so I thought CH3CH2OH + H2SO4 would work well.
d) This one confuses me. A strong base, a poor nucleophile (because of steric hindrance), a secondary alkyl halide, and a polar protic solvent. So it should be E2, right? But I only got 2 points out of 5 for putting the E2 product. He did say he wanted all of the products and I only drew the major product, so maybe that's it. So it is E2, right?
f) This one sort've puzzles me. It's obviously an elimination reaction, but I don't know if I should eliminate both OH groups at once and form a double bond between the two like I did or if I should only eliminate one OH group. Or would all possibilites be products with one of them being the major one? I don't see how I'm supposed to be able to figure that out
g) So OCH3 gets protonated by HBr, then OCH4 leaves and Br attacks in an E1/Sn1 mechanism, I think. I wasn't sure why he put 2HBr and that always makes me nervous because I don't see the difference between 2HBr and just HBr. Also, Sn1 would be the major product since Br is a poor base, right? Or maybe the mechanism is Sn2 and there isn't any E2 at all. Gah.
h) Well, it looks like I need a nucleophile that gives only Sn2 products. That would be a poor base and a strong nucleophile. I thought -SMe might work, since -SH is supposed to be a poor base and a good nucleophile, but I wasn't sure if the same was true for -SMe.
i) Poor base, poor nucleophile, secondary alkyl halide, so Sn1/E1. I wasn't sure which would be the major product though, Sn1 or E1? Is it always just Sn1? I'm confused on that.
j) Poor base, poor nucleophile, tertiary alkyl halide, so Sn1/E1. Again, I don't see how to figure out which is the major product.
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