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Here's the question in my book (see picture)

The question

Option A is a standard reaction which gives a carboxylic acid.

Option B is definitely wrong because an acid base reaction will take place and CH4 will be formed after the first step. CO2 will not react with the methane gas.

So without knowing about option C, I can safely tick option A. But what happens in option C? Here's the solution provided in the book.

The solution provided

Why cannot a carbonyl group and Grignard reagent be present in same substance? Also, what will be the reaction?

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    $\begingroup$ Hmm? Does CH3MgBr react with acetone? $\endgroup$ – user55119 Mar 24 at 18:36
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    $\begingroup$ In other words, did you think about why your teacher advised you to not wash your glassware with acetone before doing Grignard reaction? :-) $\endgroup$ – Mathew Mahindaratne Mar 24 at 19:57
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You should look at two things:

1) Will the reaction stay on course? If you add water to the Grignard reagent first, without the carbon dioxide initially, what do you get? Is it something that will get you your carboxylic acid when you add the carbon dioxide?

2) Can you make the Grignard reagent to begin with? Here again you are asking the reaction to stay on course; if the Grignard function can react with another functional group in the molecule, it will do so either within the molecule or as an intermolecular reaction between two of the molecules. Then you no longer have your Grignard reagent.

Only one of the given possibilities works against both of these questions, so there is your answer.

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