[Nakoseda]

I'm studying for my Organic chem exam and one of the practice problems is as follows

"When the following alkyl bromide is treated with potassium hydroxide in ethanol, a racemic mixture of alcohols is obtained. Draw the structures of both alcohols, clearly label the sterochemistry for both products. draw a detailed mechanism to account for their formation"


I'm not really sure how to approach this question.

The alkyl bromide in question  for reference is 2-Bromobutane

[OrganicDan96]

you need to show your working before anyone will answer your question. first of all what do you know about the? what do you know about steriochemistry?

[Nakoseda]

you need to show your working before anyone will answer your question. first of all what do you know about the? what do you know about steriochemistry?

Based on my knowledge, when a secondary alkyl halide reacts with a strong nucleophile like OH-, It should be an E2 reaction. But, clearly, based on the question, if an alcohol is obtained, that can't possibly be the case. I'd assume it has to be an SN2 reaction, but i'm not sure why

So I guess to narrow down my question, I'm not quite sure why this reaction is a Sn2 reaction and not an E2 reaction.


As far as the mechanism itself is concerned if I just assume it's a Sn2 Reaction, I'm able to draw out the mechanism fairly easily. And as far as the stereochemistry goes, I'm able to determine which of the two products is the R enantiomer and which is the S

[kriggy]

Based on my knowledge, when a secondary alkyl halide reacts with a strong nucleophile like OH-, It should be an E2 reaction. But, clearly, based on the question, if an alcohol is obtained, that can't possibly be the case. I'd assume it has to be an SN2 reaction, but i'm not sure why

If it reacts with strong nucleophile you get SN2 reaction. The elimination is favoured by use of hindered bases. Even alkoxide base such as EtO^- give some amount of elimination product and with more hindered such as tbuOK you get barely any substitution at all.

Anyway back to your original question:
if you know it is a SN2 reaction, how do you explain the formation of both stereoisomers?

[Nakoseda]

Based on my knowledge, when a secondary alkyl halide reacts with a strong nucleophile like OH-, It should be an E2 reaction. But, clearly, based on the question, if an alcohol is obtained, that can't possibly be the case. I'd assume it has to be an SN2 reaction, but i'm not sure why

If it reacts with strong nucleophile you get SN2 reaction. The elimination is favoured by use of hindered bases. Even alkoxide base such as EtO^- give some amount of elimination product and with more hindered such as tbuOK you get barely any substitution at all.

Anyway back to your original question:
if you know it is a SN2 reaction, how do you explain the formation of both stereoisomers?

Thanks for the help,

It turns out there was a typo in the question.

It was supposed to be water instead of KOH in ETOH.

which makes it an sn1 mechanism.