Q.What are the IUPAC names of the insecticide DDT and benzenehexachloride? Why is their use banned in India and other countries?

Concept: Organic Compound Applications – DDT and BHC (benzenehexachloride) are persistent organic pollutants (POPs) that accumulate in the environment and living tissues.

Reasoning:

1. IUPAC names:
   • DDT: 2,2-bis(4-chlorophenyl)-1,1,1-trichloroethane (or 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane).
   • Benzenehexachloride (BHC): 1,2,3,4,5,6-hexachlorocyclohexane (commonly the $\gamma$-isomer is lindane). …

Why these compounds were used — and why they became a problem

DDT and BHC are organochlorine insecticides. They were once hailed as miracle chemicals: cheap, stable, and deadly to a wide range of insect pests. DDT alone is credited with controlling malaria and typhus in the mid-20th century. But that very stability turned into a curse. These compounds do not break down easily in the environment. They dissolve in fats, not water, so they accumulate in the fatty tissues of animals and move up the food chain — a process called biomagnification.

At the top of the food chain — birds of prey, fish, and humans — the concentrations become high enough to cause reproductive failure, neurological damage, and cancer. Rachel Carson’s 1962 book Silent Spring brought this to public attention, and by the 1970s most countries began banning or severely restricting their use.

The IUPAC names — step by step

1. DDT

The common name DDT comes from Dichloro-Diphenyl-Trichloroethane. Let’s build the IUPAC name systematically.

• The parent structure is ethane (2 carbons).
• On one carbon (C1), three chlorine atoms are attached — that’s the trichloro part.
• On the other carbon (C2), two phenyl groups (benzene rings) are attached. But each phenyl ring has a chlorine atom at the para position (position 4).
• So each ring is a 4-chlorophenyl group.

Putting it together: the central carbon (C2) carries two 4-chlorophenyl groups, and C1 carries three chlorines. The full IUPAC name is:

2,2-bis(4-chlorophenyl)-1,1,1-trichloroethane

The prefix bis is used instead of di because the two identical substituents are complex groups (4-chlorophenyl), not simple atoms.

2. Benzenehexachloride (BHC)

The name “benzenehexachloride” is misleading — it suggests a benzene ring with six chlorines attached, but the actual structure is a saturated ring. The correct chemical name is 1,2,3,4,5,6-hexachlorocyclohexane.

• The parent is cyclohexane (a six-carbon ring, all single bonds).
• Six chlorine atoms replace six hydrogen atoms, one on each carbon.
• The locants 1,2,3,4,5,6 indicate that every carbon bears a chlorine.

Why they are banned …

Concept: IUPAC Nomenclature & Environmental Persistence of Organochlorine Pesticides

Method: Systematic IUPAC Naming from Common Names

Step 1: Identify the parent hydrocarbon chain and substituents for DDT.

• DDT stands for Dichloro-Diphenyl-Trichloroethane.
• The core structure is ethane ($\text{C}_2\text{H}_6$), with three chlorine atoms on one carbon (making it a trichloro derivative) and two phenyl rings on the other carbon.
• The IUPAC name is built by naming the substituents alphabetically.

Step 2: Write the IUPAC name of DDT.

• IUPAC name: 1,1,1-Trichloro-2,2-bis(4-chlorophenyl)ethane

Step 3: Identify the parent hydrocarbon and substituents for benzenehexachloride (BHC).

• Benzenehexachloride is a cyclohexane ring with six chlorine atoms attached (one per carbon).
• The common name “benzenehexachloride” is misleading — it is not benzene but a saturated cyclohexane derivative.
• The correct IUPAC name uses the cyclohexane parent.

Step 4: Write the IUPAC name of BHC.

• IUPAC name: 1,2,3,4,5,6-Hexachlorocyclohexane

Why Are They Banned?

Reason 1: High Persistence (Non-Biodegradability)

• Both DDT and BHC are organochlorine compounds with very stable carbon-chlorine bonds.
• They do not break down easily in the environment — they can remain in soil and water for decades.
• This leads to bioaccumulation (build-up in organisms) and biomagnification (increase in concentration up the food chain).

Reason 2: Toxicity to Non-Target Organisms

• They are broad-spectrum insecticides — they kill beneficial insects (like bees and pollinators) and harm birds, fish, and mammals.
• DDT is infamous for causing egg-shell thinning in birds of prey (e.g., eagles, falcons), leading to population decline.

Reason 3: Health Hazards to Humans …

Here are the common mistakes students make on this question, along with the correct understanding and exam-smart strategies to avoid them.

1. Confusing the IUPAC Name of DDT

The Mistake:

Students often write the IUPAC name as "Dichlorodiphenyltrichloroethane" — which is actually the common or trivial name, not the systematic IUPAC name.

Why this happens:

The abbreviation "DDT" itself stands for Dichloro-Diphenyl-Trichloroethane. It is easy to assume this is the official IUPAC name.

How to Avoid It:

• Memorise the correct IUPAC name: The systematic IUPAC name is: 1,1,1-Trichloro-2,2-bis(4-chlorophenyl)ethane
• Break it down:
  • The parent chain is ethane (2 carbons).
  • One carbon has three chlorine atoms: 1,1,1-trichloro.
  • The other carbon has two 4-chlorophenyl groups (benzene rings with chlorine at the para position).
• Exam tip: If the question asks for the "IUPAC name," never write "dichlorodiphenyltrichloroethane." That is a common name and will lose marks.

2. Writing the Wrong Formula for Benzenehexachloride (BHC)

The Mistake:

Students write the formula as C₆H₆Cl₆ but then incorrectly draw the structure as a benzene ring with six chlorine atoms attached (like a hexachlorobenzene).

Why this happens:

The name "benzenehexachloride" sounds like benzene + 6 chlorines, so students assume the benzene ring remains aromatic.

How to Avoid It:

• Understand the addition reaction: BHC is made by adding chlorine to benzene in the presence of sunlight. This is an addition reaction, not substitution.
• Correct structure: The benzene ring loses its three double bonds. The correct IUPAC name is: 1,2,3,4,5,6-Hexachlorocyclohexane
• Key point: The ring is now a cyclohexane (saturated), not benzene. All six carbons are $sp^3$ hybridised.
• Exam tip: Always write the IUPAC name as 1,2,3,4,5,6-hexachlorocyclohexane (often abbreviated as HCH or BHC). Never draw it with alternating double bonds.

3. Giving Vague or Incomplete Reasons for the Ban

The Mistake:

Students write only: "They are toxic" or "They cause pollution." This is too vague and loses marks.

Why this happens:

Students remember that these compounds are harmful but do not recall the specific environmental and health reasons.

How to Avoid It:

• Learn the two key properties that make them dangerous:
  1. Persistence (Non-biodegradability): DDT and BHC do not break down easily in the environment. They remain in soil and water for decades.
  2. Bioaccumulation & Biomagnification: These compounds are fat-soluble. They accumulate in the fatty tissues of organisms and their concentration increases at each trophic level in a food chain.
• Specific health effects:
  • DDT: Affects the nervous system, is a suspected carcinogen, and causes thinning of eggshells in birds (leading to population decline).
  • BHC (Lindane): Can cause liver and kidney damage, and is also a neurotoxin.
• Exam tip: Write a structured answer:
  • "They are non-biodegradable and persist in the environment."
  • "They undergo biomagnification in food chains, reaching toxic levels in top predators."
  • "They cause long-term health issues such as cancer, neurological damage, and reproductive disorders."

4. Mixing Up the Banned Status of DDT and BHC

The Mistake:

Students say both are completely banned worldwide for all uses.

Why this happens:

News and textbooks often say "banned," but the reality is more nuanced. …