Grignard

[NA19]

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Can someone explain this rxn?

 

[onedirection]

I don't think that's the full reaction



Unless the R group because it is partially negative extracts that terminal Hydrogen from the alkyne and gives up the MgBr group to replace the H, but I'm not the best with orgo...regardless I dont think it's the full reaction because Grignard usually adds a C-C bond or adds an O or OH or something like that

 

[FeinMS]

Example of Grignard reagent used as a base. Grignard reagents are usually strong bases.

 

[monkeyvokes]

Looks like there should be four choices below, A B C and D, and you're only showing choice A (the wrong answer). The right answer would be an acetylide anion.

Grignard is a strong base, so it takes the terminal proton and makes an acetylide anion.

 

[monkeyvokes]

Example of Grignard reagent used as a base. Grignard reagents are usually strong bases.

Gignards are strong bases, but are also nucleophilic.

 

[FeinMS]

Looks like there should be four choices below, A B C and D, and you're only showing choice A (the wrong answer). The right answer would be an acetylide anion.

Grignard is a strong base, so it takes the terminal proton and makes an acetylide anion.

And the lone pair from deprotonation is readily donated to MgBr which is a lewis acid

 

[NA19]

The answers said that A was the right answer which is why I showed it. How do you know when a grignard will yield an alcohol or when it will do something like this?

 

[monkeyvokes]

The answers said that A was the right answer which is why I showed it. How do you know when a grignard will yield an alcohol or when it will do something like this?

What looks like a covalent bond there between the acetylide anion and MgBr+ must be representing an ionic bond then?

 

[Romz]

Can someone explain this rxn?

Guys, gringard reagents make good nucleophiles because of the C d- charge due to e- donating effects of the metal.

The d- Carbon will attack the C d+ carbon of the triple bond, which happens to be d+ dipole because of the e- withdrawing effects of the 3x bond, and kick the hydrogen.

Grignard reagents are not bases in this respect. Yeah, the C has an induced d- dipole because of the Mg, which makes it a nucleophile, but that doesn't mean it'll act as a base.

Plenty of other ways to deprotonate to make acetylene ion 😛 No need for G reagent

 

[monkeyvokes]

The d- Carbon will attack the C d+ carbon of the triple bond, which happens to be d+ dipole because of the e- withdrawing effects of the 3x bond, and kick the hydrogen.

Then why doesn't it show the formation of a new carbon-carbon bond?

Grignard reagents are not bases in this respect. Yeah, the C has an induced d- dipole because of the Mg, which makes it a nucleophile, but that doesn't mean it'll act as a base.

Plenty of other ways to deprotonate to make acetylene ion 😛 No need for G reagent

Classic example of grignard preferentially acting as a base:

"The Grignard reagents are highly basic and can react with protic compounds like water, acids, alcohols, 1-alkynes etc."

 

[Romz]

Then why doesn't it show the formation of a new carbon-carbon bond?



Classic example of grignard preferentially acting as a base:

"The Grignard reagents are highly basic and can react with protic compounds like water, acids, alcohols, 1-alkynes etc."

Wow, you're right about that. I just checked my notes and there are certain cases in which G reagents will deprotonate instead of add to Carbon, as is the case for Carboxylic Acids...


This is the case for Acetylene too according to my notes...




It would help to see the other answer choices so we could state why they're wrong....

 

[monkeyvokes]

Wow, you're right about that. I just checked my notes and there are certain cases in which G reagents will deprotonate instead of add to Carbon, as is the case for Carboxylic Acids...


This is the case for Acetylene too according to my notes...




It would help to see the other answer choices so we could state why they're wrong....

I agree, hopefully OP will deliver or say what the passage is from