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Chemistry Forums for Students => Organic Chemistry Forum => Organic Chemistry Forum for Graduate Students and Professionals => Topic started by: azmanam on July 20, 2009, 07:13:55 AM

Title: Problem of the Week 07/20/09
Post by: azmanam on July 20, 2009, 07:13:55 AM

QUESTION: Explain the stereochemical results for the following transformation

Title: Re: Problem of the Week 07/20/09
Post by: Dan on July 20, 2009, 07:25:54 AM

Initially S_N2 displacement of mesylate by iodide, then S_N2 displacement of that iodide by iodide (eventually) racemises the system?

Title: Re: Problem of the Week 07/20/09
Post by: azmanam on July 20, 2009, 03:41:29 PM

Yup.  Two quick ones in a row... I guess I'll have to start making them harder :) 

Iodide is a great nucleophile and a great leaving group.  Initial formation of the optically pure iodide is soon attacked by the good nucleophile I^- to liberate the good leaving group I^- to give the iodide with the opposite configuration.  Repeated attack of I^- to liberate I^- eventually provides the racemate.  No S_N1 mechanism is proposed.

I've updated the LAH reduction with a different focus.  Take a look at that if you want another challenge this week. http://www.chemicalforums.com/index.php?topic=33985.0