The correct order of reactivity of PhMgBr with
`underset((I))(Ph-underset(C)overset(O)overset(||)(C)-Ph)" " underset((II))(CH_(3)-overset(O)overset(||)(C)-H)" " underset((III))(CH_(3)-overset(O)overset(||)(C)-CH_(3))` is

Options

A. `(i) gt (ii) gt (iii)`
B. `(iii) gt (ii) lt (i)`
C. `(ii) lt (iii) lt (i)`
D. `(i) lt (iii) lt (ii)`

Answer

To determine the correct order of reactivity of the Grignard reagent (PhMgBr) with the given carbonyl compounds, we need to analyze the electron donating or withdrawing effects of the substituents on the carbonyl carbon. The compounds in question are:

1. (I) Ph-C(=O)-Ph (benzophenone)
2. (II) CH3-C(=O)-H (acetaldehyde)
3. (III) CH3-C(=O)-CH3 (acetone)

### Step 1: Understand the nature of the Grignard reagent
Grignard reagents, such as PhMgBr, act as nucleophiles. The carbon atom in the Grignard reagent has a partial negative charge, making it highly reactive towards electrophilic centers, such as the carbonyl carbon in aldehydes and ketones.

### Step 2: Analyze the carbonyl compounds
- **(I) Benzophenone (Ph-C(=O)-Ph)**: The carbonyl carbon is bonded to two phenyl groups, which are electron-donating through resonance. This reduces the electrophilicity of the carbonyl carbon, making it less reactive towards nucleophiles.

- **(II) Acetaldehyde (CH3-C(=O)-H)**: The carbonyl carbon is bonded to a methyl group and a hydrogen. The methyl group is a weak electron-donating group, but hydrogen does not donate electrons. Thus, the carbonyl carbon retains a relatively high electrophilicity, making it more reactive than benzophenone.

- **(III) Acetone (CH3-C(=O)-CH3)**: The carbonyl carbon is bonded to two methyl groups, which are electron-donating. This reduces the electrophilicity of the carbonyl carbon more than in acetaldehyde, making it less reactive than acetaldehyde but more reactive than benzophenone.

### Step 3: Determine the order of reactivity
Based on the analysis:
- Acetaldehyde (II) is the most reactive due to the presence of a hydrogen atom, which does not donate electrons.
- Acetone (III) is less reactive than acetaldehyde because both substituents are methyl groups, which donate electrons.
- Benzophenone (I) is the least reactive due to the presence of two phenyl groups that donate electrons through resonance.

Thus, the correct order of reactivity is:
**(II) > (III) > (I)**

### Final Answer
The correct order of reactivity of PhMgBr with the given carbonyl compounds is:
**(II) > (III) > (I)**

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