[megs]

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!

[Demotivator]

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.

[movies]

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.

[Mitch]

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.

[bronzezt]

you can read the attach ,it will be useful to you

[Rotwang]

I hope this will help you (short and clear, only mechanistic view)