Question

Which halide will be least reactive in respect to hydrolysis?
A. Vinyl chloride
B. Allyl chloride
C. Ethyl chloride
D. T-butyl chloride

Answer 1

Hint: Hydrolysis may be defined as a double decomposition reaction where water is used as one of the reactants.

Complete Step by Step Solution:
The mono-halides derived from alkenes are known as alkenyl halides e.g., vinyl chloride \[({\rm{C}}{{\rm{H}}_{\rm{2}}} = {\rm{CH}} - {\rm{Cl}})\].
The reactions of vinyl chloride at the chlorine atom are strikingly different from those of alkyl chlorides. It does not react with nucleophilic reagents giving substitution products. For example, vinyl chloride is not hydrolysed by sodium hydroxide.

On the other hand, ethyl chloride can be hydrolysed by sodium hydroxide as shown below.
The reason for the non-reactivity of the halogen atom is that the \[{\rm{C}} - {\rm{Cl}}\] bond in vinyl chloride is stronger than one in alkyl chloride, and is therefore less readily broken. This is so because a p orbital on chlorine interacts with the p orbital on the adjacent carbon atom. The new delocalized orbital permits the movement of the unshared electrons of the p orbital of the halogen atom and those of the \[\pi \]orbital of the double bond such that, the \[{\rm{C}} - {\rm{Cl}}\] bond becomes slightly stronger than in alkyl chloride. Also, the delocalization of electrons makes the chlorine atom slightly less negative and the adjacent carbon slightly more negative. This makes the carbon holding the chlorine less prone to nucleophilic attack.
Hence, the halide less reactive towards hydrolysis is vinyl chloride.
Therefore, option A is correct.

Note: Vinyl chloride is a colourless gas under ordinary conditions. Liquid substance boils at \[ - {13.9^0}\]. Vinyl chloride polymerizes when heated in an inert solvent in presence of dibenzoyl peroxide. The product is polyvinyl chloride (PVC).