Write the structures of A and B in the following reaction
`CH_(3)MgBr underset((ii)H_(3)O^(+))overset((i)CO_(2))to A overset(PCl_(5))toB`

Explanation

To solve the given reaction step-by-step, we will identify the structures of compounds A and B based on the provided reaction sequence.

### Step 1: Identify the starting material
The starting material is **CH₃MgBr**, which is a Grignard reagent. Grignard reagents are highly reactive organomagnesium compounds.

### Step 2: Reaction with CO₂
When CH₃MgBr reacts with CO₂, the nucleophilic carbon (from the CH₃ group) attacks the electrophilic carbon of the carbon dioxide molecule. This results in the formation of a carboxylate intermediate.

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