Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: megs on October 03, 2004, 10:39:59 PM
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Hi,
I'm studying Grignard Reagent formation in my Ochem2 class. The book is very vague on the mechanism of the synthesis of the Grignard Reagent.
I understand that the process goes like: RX + Mg --> RMgX
But I am interested in learing how the electrons flow, as the book does mention it is a two step process, but does not mention how the Mg combines (i.e. first with the R and then the X?)
Thanks!
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The C-X bond is polarized with partial positive charge on C. Metallic Mg is an electron donor and bonds to the electrophilic C, displacing the X. Now the C gets a partial neg charge and Mg positive. The X- is left to bond with Mg.
However, exactly what the intermediate looks like (a triangle of bonds?) is not well understood.
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Another posibility is that the oxidative insertion occurs through a radical process. If this is the case, then the mechanism is almost exactly like Demotivator described, but instead think of the R-X bond as being cleaved homolytically (into two radicals) and then the Mg donates one electron to each species (R and X) to give Mg2+ along with R- and Br-.
At any rate, I don't think anyone really knows how oxidative insertion works for sure.
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Remember you are taking an organic chem class not an inorganic class. Mg enters the bond through a oxidative insertion as movies said. If you want to learn more about it, or learn that the mechanism for it is still poorly understood take an inorganic class next.
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you can read the attach ,it will be useful to you
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I hope this will help you (short and clear, only mechanistic view) ;)
(https://www.chemicalforums.com/proxy.php?request=http%3A%2F%2Fwww.cm.utexas.edu%2Fbauld%2Funit5_radicals_files%2Fimage033.gif&hash=9c70836ad7547ed74e5e04bda99c00a40944fe52)