Propyl Magnesiumbromide Structure

[Lawrence Tran 2H]

In Week 1 Question 10 on Achieve, on the of the problems uses propyl magnesiumbromide. In the illustration depicting the chemical equation, the magnesium atom is separated by a + sign from the rest of the molecule, as if it was its own reactant. I was wondering why they are separated in the illustration? Or is propyl magnesiumbromide even 1 molecule?

[Caleb_Mei_1J]

Hey Lawrence!

That's because in the problem, it states that propyl magnesiumbromide, the excess reactant, is made by reacting 1‑bromopropane with metallic magnesium. The chemical equation simply reflects that these two compounds, when reacted together, make propyl magnesiumbromide.

I hope this helps!

[KyleNagasawaDisc3C_Chem 14B2022W_]

Hey Lawrence,

The reaction depicted in question 10 is a popular named reaction called Barbier Coupling, where a metal (eg. Sn) undergoes oxidative addition by coordination of two anionic ligands to produce a reactive metallorganic species, which can react with electrophilic functional groups and moieties (here, a carbonyl). Think of the Magnesium as being "inserted" between the C-Br bond, producing an anionic-like highly-nucleophilic carbon species due to the high electropositivity of the metal atom. This reaction is particularly noteworthy because it allows for the in situ ("in reaction vessel") development of metalorganic species, such as propyl magnesium bromide (here, a Grignard is created), which would otherwise autooxidize in air and start a dangerous fire if developed prior to placement in the reaction flask. The primary product would be the same if a propyl magnesium bromide was added to the reaction, although percent yields would likely differ.