Chemical Forums

Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Mizushina Rena on January 24, 2016, 05:56:46 AM

Title: Finkelstein reaction
Post by: Mizushina Rena on January 24, 2016, 05:56:46 AM

Hello,

I am not sure if the stereochemistry of the following Finkelstein reaction (Walden inversion) is correct :

(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Ffs5.directupload.net%2Fimages%2F160124%2Ffv3554r8.png&hash=52e188c06a9f16d9357a4bd5fde9212356d2e67b) (http://www.directupload.net)

Title: Re: Finkelstein reaction
Post by: sjb on January 24, 2016, 07:43:48 AM

How would you tell? Is either epimer favoured?

Title: Re: Finkelstein reaction
Post by: Mizushina Rena on January 24, 2016, 09:49:27 AM

The task was to name the product(s). I think that we have here a finkelstein reaction with the walden inversion. That means we except only the (R)-product.  Because it follows a SN2-mechanism.

Title: Re: Finkelstein reaction
Post by: BRSM on February 07, 2016, 02:46:13 PM

That's the probably the product you're expected to give - the reaction is S_N2 and therefore goes with inversion.

However, it's important to note that in reality, depending on temperature and reaction time you can get iodide displacing iodide in the product, which is a degenerate transformation EXCEPT for stereochemistry. Thus, you'd probably get mixtures of iodide isomers due to this side reaction. If you do a Finkelstein at a stereogenic bromide, you rarely get total conservation of er/dr for this reason.