Question

Write the product of the following reactions along with their mechanism:
i) p-nitrochlorobenzene + NaOH (623 K, 300 atm), then H⁺ → [A]
ii) Chlorobenzene + CH₃COCl (anhydrous AlCl₃) → [B] + [C]
iii) CH₃–CH=C(CH₃)₂ + HBr → [D]
OR
Write short notes on the following: i) D.D.T. ii) Freon iii) Carbon tetrachloride

Hint:

For Option 1: the para NO2 group activates chlorobenzene toward nucleophilic substitution (gives p-nitrophenol), CH3COCl with AlCl3 is Friedel-Crafts acylation giving o- and p-chloroacetophenone, and HBr without peroxide follows Markovnikov rule. For Option 2: DDT is an insecticide, Freon is a CFC refrigerant, and CCl4 is a solvent and fire-extinguisher liquid.

Answer 1

Option 1 (alternative explanation):
Step 1 (reaction i): In p-nitrochlorobenzene the chlorine sits on a carbon that has been made electron-poor by the para nitro group. Because of this, the electron-rich OH^- ion is able to attack that carbon even though it is part of a benzene ring. The intermediate carbanion drops its negative charge onto the oxygen atoms of the NO₂ group through resonance, which makes it stable; chloride ion then departs. After adding acid we obtain [A] = p-nitrophenol.
Step 2 (reaction ii): Think of this as attaching a CH₃CO group to the ring. AlCl₃ removes Cl from acetyl chloride to create the acylium electrophile CH₃CO⁺. As the ring already carries Cl, which is an ortho/para director, the acyl group enters chiefly at the para position and partly at ortho. Hence [B] = p-chloroacetophenone (major) and [C] = o-chloroacetophenone (minor). A proton is finally lost so the ring turns aromatic again.
Step 3 (reaction iii): For CH₃CH=C(CH₃)₂ + HBr the guiding idea is that hydrogen adds to the double-bond carbon that already holds more hydrogen atoms. This leaves the positive charge on the fully substituted carbon, a tertiary carbocation, which is the most stable option. Bromide then bonds to that carbon, so [D] = 2-bromo-2-methylbutane. There is no peroxide, so no anti-Markovnikov (free-radical) product forms.

Option 2 (alternative wording):
Step 1 (DDT): Full chemical name dichlorodiphenyltrichloroethane. It is a cheap and powerful insecticide. Because it does not break down easily in nature (non-biodegradable), it lingers in soil and enters food chains, harming fish and birds, which is why most countries have banned it. It is manufactured from chlorobenzene and chloral.
Step 2 (Freon): Trade name for CFC refrigerant gases such as CCl₂F₂ (Freon-12) and CCl₃F (Freon-11). They are stable, non-toxic and non-flammable, which made them ideal for refrigerators, air conditioners and spray cans; but that same stability lets them drift up to the stratosphere, where ultraviolet light frees Cl atoms that catalytically break ozone down.
Step 3 (Carbon tetrachloride): CCl₄ is a dense, sweetish-smelling liquid that dissolves fats and oils, so it served as a solvent and as the liquid in Pyrene fire extinguishers, where its heavy vapour smothers flames. However, breathing it damages the liver and nervous system, and in a fire it can generate poisonous phosgene, so its use has been greatly cut down.