# Haloalkanes and Haloarenes

## Chemistry

### NCERT

1   Among the isomeric alkanes of molecular formula $C_5 H_{12}$ identify the one that one photochemical chlorination yields$\\$ (i) A single monochloride$\\$ (ii) Three isomeric monochlorides.$\\$ (iii) Four isomeric monochlorides.

##### Solution :

(i) Neopentane$\\$ As all the H-atoms are equivalent, the replacement of any one of them give the same product.$\\$ (ii)$\overset{a}{CH_3} \overset{b}{CH_2} \overset{c}{CH^2} \overset{d}{CH_2} \overset{a}{CH_3}$ n-pentane. a, b, c are the three sets of equivalent hydrogens.$\\$ Therefore, three isomeric monochlorides are possible.$\\$ (iii)iso-pentane, there are four sets of equivalent hydrogens designated as a,b,c,d. Thus, four isomeric monochlorides are possible.

2   Write structures of the following compounds:$\\$ (i) $2 -$ chloro$-3$ methylpentane$\\$ (ii) $1-$ chloro$- 4 -$ ethylcyclohexane$\\$ (iii)$4 -$ tert .Butyl$-3-$ iodoheptane$\\$ (iv)$1, 4 -$Dibromobut$- 2 -$ ene$\\$ (v) $1-$ Bromo$- 4 -$ sec/ butyl$- 2 -$methylbenzene.

##### Solution :

3   Why is sulphuric acid not used during the reaction of alcohols with $Kl$?

##### Solution :

$H_2 SO_4$ is an oxidizing agent. It oxides $Hl$ produced during the reaction to $I _2$ and thus prevents the reaction between an alcohol and $HI$ to from alky iodide. In order to prevent this, a non- oxidising acid like $H _3 PO _3$ is used which prevents the oxidation of $HI$.$\\$ $2 KI + H_2 SO_4 \to 2 KHSO_4 + 2 HI \to I_2$

4   Write structures of different dihalogen derivatives of propane

##### Solution :

Four isomers are possible. There are:$\\$ $Br- CH_2 CH_2 CH_2 - Br 1,3 ,-$dibromopropane

5   Among the isomeric alkanes of molecular formula $C_5 H_{12}$ identify the one that one photochemical chlorination yields$\\$ (i) A single monochloride$\\$ (ii) Three isomeric monochlorides.$\\$ (iii) Four isomeric monochlorides.

##### Solution :

(i) Neopentane$\\$ As all the H-atoms are equivalent, the replacement of any one of them give the same product$\\$ (ii) $CH _3 CH _2 CH _2 CH _2 CH _3$ n-pentane. a, b, c are the three sets of equivalent hydrogens.$\\$ Therefore, three isomeric monochlorides are possible.$\\$ (iii)iso-pentane, there are four sets of equivalent hydrogens designated as a,b,c,d. Thus, four isomeric monochlorides are possible.