Grignard with acid?

[diene]

I was doing Chad's quiz and I got a little confused.

In this question, the product is the same as the reactant.

"This question is a little tricky.* A Grignard reagent shouldn't be in any kind of protic solution as it will be protonated by anything protic in an acid-base reaction which effectively destroys the Grignard reagent as is the case here.* In the first step, the Grignard reagent deprotonates the alcohol.* The addition of H3O+ simply reprotonates the alkoxide converting it back into an alcohol and so the product is the same as the original reactant (choice A)."

Vs. this question:

you actually get a different product-

Can someone explain this to me? How do I know when Grignard and acid will not work? I know that if you add a grignard and then add acid in the second step, it should be ok. But using these two examples, I don't understand how the first one is different than the second one.

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[diene]

Not sure why the image is not working.If you replace the ***** with c o u r s e s a v e r, it should work

If you have access to Chad's quizzes, 643 and 641

 

[Mr. Thirsty]

Weird. I feel like number one should definitely be reduced to an alcohol because the h30+ is added on the second step, so the grignard should work....

 

[ijk90825]

I was doing Chad's quiz and I got a little confused.

In this question, the product is the same as the reactant.

"This question is a little tricky.* A Grignard reagent shouldn't be in any kind of protic solution as it will be protonated by anything protic in an acid-base reaction which effectively destroys the Grignard reagent as is the case here.* In the first step, the Grignard reagent deprotonates the alcohol.* The addition of H3O+ simply reprotonates the alkoxide converting it back into an alcohol and so the product is the same as the original reactant (choice A)."

Vs. this question:

you actually get a different product-

Can someone explain this to me? How do I know when Grignard and acid will not work? I know that if you add a grignard and then add acid in the second step, it should be ok. But using these two examples, I don't understand how the first one is different than the second one.

As far as I understand the topic, 2. H3O is for the protonation of O- after phenyl group is attached (did I word it right? lol) so it'll be added after the phenyl group is attached to the tertiary carbon?

If there's a protic (-OH group in this case) then it'll destroy grignard and it what you wrote explains it. hope this makes sense lol

So basically H3O+ is the protic solution they mean, they meant the OH group

I'm not an expert in orgo :/ sorry if it was confusing

 

[biomolecmed]

Grignard is a strong base, therefore will react with anything that has an acidic proton such as alcohols or acids. If you use Grignard together with acid or alcohol or water, not in a second step, then those solutions will simply react with grignard and would not allow grignard to do its job. Hope this helps.

 

[gettheleadout]

Not sure why the image is not working.If you replace the ***** with c o u r s e s a v e r, it should work

If you have access to Chad's quizzes, 643 and 641

Chad's website is blocked through our text filter.

Grignard is a strong base, therefore will react with anything that has an acidic proton such as alcohols or acids. If you use Grignard together with acid or alcohol or water, not in a second step, then those solutions will simply react with grignard and would not allow grignard to do its job. Hope this helps.

This is correct.