Question: Which one of the following halides contains $\text{C}_{\text{sp}^2} - \text{X}$ bond?
Step 1 (Definition & Structural Identification): [0.5 Mark]
The hybridization of a carbon atom bonded to a halogen ($\text{X}$) is determined by the number of sigma bonds and lone pairs. A $\text{C}_{\text{sp}^2} - \text{X}$ bond occurs when the carbon atom attached to the halogen is double-bonded to another carbon atom (trigonal planar geometry).
- Alkyl halide: $\text{R}-\text{CH}_2-\text{X}$ (Carbon is $\text{sp}^3$ hybridized).
- Allyl halide: $\text{CH}_2=\text{CH}-\text{CH}_2-\text{X}$ (Carbon attached to $\text{X}$ is $\text{sp}^3$ hybridized).
- Benzyl halide: $\text{C}_6\text{H}_5-\text{CH}_2-\text{X}$ (Carbon attached to $\text{X}$ is $\text{sp}^3$ hybridized).
- Vinyl halide: $\text{CH}_2=\text{CH}-\text{X}$ (Carbon attached to $\text{X}$ is $\text{sp}^2$ hybridized).
Step 2 (Structural Analysis): [0.25 Mark]
In Vinyl halide ($\text{CH}_2=\text{CH}-\text{X}$), the carbon atom directly bonded to the halogen atom is part of a carbon-carbon double bond. According to VSEPR theory, a carbon atom involved in one double bond and two single bonds exhibits $\text{sp}^2$ hybridization.
$$ \text{H}_2\text{C} = \text{C}(\text{H}) - \text{X} \implies \text{C}_{\text{sp}^2} - \text{X} $$Step 3 (Final Concluded Answer): [0.25 Mark]
The correct option is (D) Vinyl halide.
💡 EL10 Concept Insight: Think of hybridization like a carbon atom's "handshake" style; if the carbon is already busy holding hands (double bond) with a neighbor, it only has three "sp2" arms left to share, making it the perfect match for a vinyl halide bond!