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While learning about the Grignard reagent I was taught this by my teacher, but I couldn’t justify why it was so..
I cannot see how Grignard reagent would react differently in basically an ethereal solvent..
So i needed a justification as in why this was happening. Thanks

Effect of solvent used as taught by my professor

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    $\begingroup$ What is a 'resonance stabilised bond'? Never heard of such a thing. $\endgroup$
    – orthocresol ♦
    Jan 25, 2019 at 12:10
  • $\begingroup$ @orthocresol I think what it means is that the carbon-halogen bond has a partial double bond character due to resonance. Of course, it is poorly worded as shown $\endgroup$
    – Yusuf Hasan
    Jan 25, 2019 at 12:48
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    $\begingroup$ There are 2 different things when comparing ether and THF: 1) the electron density of oxygen in THF is higher (it is basically ether with its arms attached in its back) so it will stabilise the organomagnesium compound better; 2) the reaction is usually carried out at reflux of the pure ether, so at a higher temperature in THF $\endgroup$
    – SteffX
    Jan 25, 2019 at 12:52
  • $\begingroup$ @SteffX But according to this formation of a Grignard reagent is a SET mechanism which doesn't involve the solvent. So are you talking about solvation of the organomagnesium compound when you talk of stabilisation? $\endgroup$
    – Yusuf Hasan
    Jan 25, 2019 at 13:03
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    $\begingroup$ @YUSUFHASAN, Alchimista — Your dreams have come true: I have posted an answer :-) $\endgroup$
    – SteffX
    Feb 22, 2019 at 16:01

1 Answer 1

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THF has a number of differences with diethyl ether:

  1. Oxygen non-bonding doublets are more available for bonding with magnesium because the 2 ethyl groups are not freely rotating around (you may think of THF as diethyl ether with its arms tied in its back).
  2. THF boils at 66°C (ether 34.6°C). Because the reaction is usually carried out so to maintain a gentle reflux, the higher boiling temperature of THF will speed up the reaction, and solubilize reactants/products better.

As @Alchimista pointed out, THF is just one of the possible solvents you can use if ether fails or gives poor yields. You can also use higher boiling ethers like dimethoxyethane.

Note: this is a collective answer asked by other users. I have been harassed. Call the police :-)

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