What happens when (i) chlorobenzene is treated with Cl2/FeCl3, (ii) ethyl chloride is treated with AgNO2, and (iii) 2-bromopentane is treated with alcoholic KOH?

(i) Chlorobenzene treated with Cl2/FeCl3:
Chlorobenzene undergoes electrophilic aromatic substitution. FeCl3 acts as a Lewis acid catalyst, generating a electrophile Cl+. This electrophile attacks the benzene ring, leading to the formation of 1,4-dichlorobenzene as the major product and some 1,2-dichlorobenzene. The reaction is relatively slow compared to alkylbenzenes because the electron-withdrawing nature of chlorine deactivates the benzene ring.

Reaction:

       Cl
       | 
Cl- +  C6H5Cl --FeCl3-->  C6H4Cl2 + HCl

(ii) Ethyl chloride treated with AgNO2:
Ethyl chloride reacts with silver nitrite (AgNO2) in a nucleophilic substitution reaction (SN1). The reaction proceeds through a carbocation intermediate. The nitrite ion (NO2-) acts as a nucleophile, and it can attack from either the nitrogen or the oxygen atom which results in a mixture of nitroethane and ethyl nitrite.

Reaction:

CH3CH2Cl + AgNO2 --> CH3CH2NO2 (nitroethane) + CH3CH2ONO (ethyl nitrite) + AgCl

(iii) 2-bromopentane treated with alcoholic KOH:
2-bromopentane reacts with alcoholic KOH in an elimination reaction (E2). The alcoholic KOH provides a strong base (ethoxide ion), which abstracts a proton from the beta-carbon (carbon adjacent to the carbon bearing the bromine atom). Simultaneously, the C-Br bond breaks, resulting in the formation of a double bond (alkene). The major product formed is 2-pentene (due to Zaitsev's rule, which states that the most substituted alkene is the major product in elimination reactions). There might be small amount of 1-pentene as a minor product.

Reaction:

CH3CHBrCH2CH2CH3 + KOH (alc) --> CH3CH=CHCH2CH3 (2-pentene) + KBr + H2O