Allyl chloride is hydrolysed more readily than n-propyl chloride. Why?
As we know that $\mathrm{S}_{\mathrm{N}} 1$ mechanism depends upon the stability of carbocation. Allyl chloride on hydrolysis gives resonance stabilised carbocation while no resonance is observed in the carbocation formed by $n$-propyl chloride.
Hence, allyl chloride undergoes hydrolysis much faster than $n$-propyl chloride.
Why is it necessary to avoid even traces of moisture during the use of a Grignard reagent?
Grignard reagents are highly reactive and react with water to give corresponding hydrocarbons.
How do polar solvents help in the first step in $\mathrm{S}_{\mathrm{N}}{ }^1$ mechanism?
Polar solvents help in the first step in $\mathrm{S}_{\mathrm{N}} 1$ mechanism because leaving group and carbocation both are stabilised by polar solvent. Polarity of a solvent depends upon the value of dielectric constant. Higher the value of dielectric constant, higher will be the polarity of the solvent, faster will be the rate of $S_N 1$ mechanism. These polar solvents can work as a nucleophile and stabilise the carbocation as follows
Write a test to detect the presence of double bond in a molecule.
Presence of double bond in a molecule is detected by following two methods:
(i) $\mathrm{Br}_2$ in $\mathrm{CCl}_4$ test ${\mathrm{When} \mathrm{Br}_2 / \mathrm{CC}_4}^2$ is added unsaturated compound then orange colour of bromine disappears and dibromoderivative is formed. (colourless).
(ii) Bayer's test When alkaline solution of $\mathrm{KMnO}_4$ is added to the solution of unsaturated compound then its pink colour disappears due to the formation of dihydroxy derivative.
Diphenyls are potential threat to the environment. How are these produced from aryl halides?
In environment, diphenyl is formed during the incomplete combustion of mineral oil and coal. It is present in the exhaust gases of vehicles and in exhaust air from residential and industrial heating devices.
Acute exposure to high levels of biphenyl has been observed to cause eye and skin irritation and toxic effects on the liver, kidneys and central /peripheral nervous system. Kidneys of animals are also affected due to the ingestion of biphenyls. In rats, fetofoxicity has been oserved if they are exposed to high levels of biphenyl.
Preparation of diphenyls from aryl halides
Aryl halides, when treated with sodium in dry ether give diphenyl. This reaction is named as Fittig reaction.