Gringard Reactions

[MedGrl@2022]

http://www.youtube.com/watch?annota...&feature=iv&src_vid=5GX2yP9trD4&v=XsTuxwOe044

So Steven from FreeLanceTeach, said that only R-MgCl, R-MgBr, and R-MgI are Gringards. Why aren't R-MgF an R-MgAt potential Gringards? Is it due to the electronegativity of those halogen atoms?

Are Grignard reactions irreversible? If so, why?

Thank you for all your help.

Sincerely,

Verónica

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[Gauss44]

So Steven from FreeLanceTeach, said that only R-MgCl, R-MgBr, and R-MgI are Gringards. Why aren't R-MgF an R-MgAt potential Gringards?

Size maybe? F having a tiny electron cloud. At being a big slow poke that would make for a slow reaction (and not hanging onto it's valence electrons as tightly)?

 

[ouroboros39]

Because its a radical mechanism the rate determining step would likely be the cleavage of the Halide-Carbon bond. Fluorine would form stronger bonds to carbon (and react slower) than the larger halides, which react much faster due to their weaker bonds with carbon. Since the reaction is exothermic, I imagine that the largest of the halides would react much faster and would be explosive, which is why we almost always see chlorine/bromine in grignards.