Question

Give reasons:
a) Alkyl halides are insoluble in water although they contain polar C-X bond.
b) Grignard reagent should be prepared under anhydrous condition.
c) Vinyl chloride is less reactive than ethyl chloride towards nucleophilic substitution reactions.

Answer 1

a) In order for a haloalkane to dissolve in water, energy is required to overcome the attraction between the haloalkane molecules and break the hydrogen bonds between water molecules. Less energy is released when new attractions are set up between the haloalkane and the water molecules as these are not as strong as the original hydrogen bonds in water. As a result, the solubility of haloalkanes in water is low.

b) Grignard reagents are very reactive. In the presence of moisture, they react to give alkanes. Therefore, Grignard reagents should be prepared under anhydrous conditions.

$RMgX+H_{2}O\to R-H+Mg\left(OH\right)X$

c) Refer Image: In vinyl chloride, the chlorine atom is attached to the double-bonded carbon. So, it forms resonance and gets the partial double bond character and thus difficult to break. Whereas the ethyl chloride does not have the property of resonance and hence it shows nucleophilic substitution reaction easily.