Question

Explain the following briefly.

Vinyl chloride is less reactive than ethyl chloride.

Answer 1

1. Structure and Hybridization: Vinyl chloride (CH₂=CHCl) has a chlorine atom attached to an sp² hybridized carbon (part of a double bond). Ethyl chloride (CH₃CH₂Cl) has a chlorine atom attached to an sp³ hybridized carbon (single bond).
2. Bond Strength: The C–Cl bond in vinyl chloride is stronger than in ethyl chloride because the sp² carbon holds electrons more tightly, making bond cleavage harder.
3. Resonance and Electron Density: In vinyl chloride, the lone pair on chlorine can overlap with the adjacent double bond’s π-electrons, making the C–Cl bond partially stabilized by resonance. This resonance stabilization reduces the tendency of the chlorine to leave, thereby decreasing reactivity in substitution or elimination reactions.
4. Effect on Reactivity: Ethyl chloride undergoes nucleophilic substitution easily (especially SN₁ and SN₂) since the alkyl halide is more reactive with the sp³ carbon. Vinyl chloride resists such substitutions because the sp² carbon does not favor carbocation formation, and the resonance stabilization further stabilizes the bond, making vinyl chloride less reactive.
5. Typical Reaction Example (Ethyl chloride):
   Substitution reaction with hydroxide ion:
   \[\mathrm{CH_3CH_2Cl} + \mathrm{OH^-} \rightarrow \mathrm{CH_3CH_2OH} + \mathrm{Cl^-}\]
6. Typical Reaction Example (Vinyl chloride): Vinyl chloride does not readily undergo substitution; addition reactions to the double bond are more common:
   \[\mathrm{CH_2=CHCl} + \mathrm{HBr} \rightarrow \mathrm{CH_3-CHBrCl}\]