`pi` bonding is not involved in

Options

A. Ferrocene
B. Dibenzene chromium
C. Zeise's salt
D. Grignard reagent

Answer

To determine which compound does not involve π bonding, let's analyze each option step by step.

### Step 1: Analyze Ferrocene
- **Structure**: Ferrocene is an organometallic compound with a sandwich structure, consisting of an iron atom sandwiched between two cyclopentadienyl (Cp) rings.
- **Bonding**: The empty d orbitals of the iron atom interact with the delocalized π orbitals of the cyclopentadienyl rings.
- **Conclusion**: Ferrocene involves π bonding.

### Step 2: Analyze Dibenzene Chromium
- **Structure**: Dibenzene chromium also has a sandwich structure, where a chromium atom is sandwiched between two benzene rings.
- **Bonding**: The vacant d orbitals of chromium interact with the delocalized π orbitals of the benzene rings.
- **Conclusion**: Dibenzene chromium involves π bonding.

### Step 3: Analyze Zisse's Salt
- **Structure**: Zisse's salt is composed of platinum with three chlorine ligands and an ethylene (C2H4) molecule.
- **Bonding**: The d electrons of platinum interact with the π bonds of the ethylene.
- **Conclusion**: Zisse's salt involves π bonding.

### Step 4: Analyze Grignard Reagent
- **Structure**: The Grignard reagent is represented as R-MgX, where R is an alkyl or aryl group and X is a halogen.
- **Bonding**: The bond between the carbon atom (from R) and magnesium (Mg) is primarily a sigma bond. There are no π bonds involved in this structure.
- **Conclusion**: Grignard reagent does not involve π bonding.

### Final Answer
Based on the analysis of all the options, the compound that does not involve π bonding is **Grignard reagent (D)**.

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