Polyhalogenated compounds Questions in English

(A) The chemical name $1, 2$-dichlorotetrafluoroethane indicates that there are two carbon atoms in the chain.
Each carbon atom is bonded to one chlorine atom and two fluorine atoms to satisfy the valency of carbon.
The structure is $Cl-CF_2-CF_2-Cl$,which can be written as $CF_2Cl-CF_2Cl$.

(D) Gammexane,also known as Lindane or $666$,is the $\gamma$-isomer of benzene hexachloride.
Its chemical structure consists of a cyclohexane ring with chlorine atoms attached to each of the six carbon atoms.
Therefore,its $IUPAC$ name is $1, 2, 3, 4, 5, 6-$hexachlorocyclohexane.

(C) Carbon tetrachloride $(CCl_4)$ is not inflammable.
Carbon tetrachloride $(CCl_4)$ is poisonous and water insoluble. It is soluble in ethanol and ether.

(C) Lewisite is $2$-chloroethenyldichloroarsine.
Its structural formula is $CHCl=CH-AsCl_2$.

(B) Gammexene,also known as $BHC$ (Benzene hexachloride) or Lindane,is produced by the addition reaction of benzene with chlorine in the presence of sunlight.
The reaction is: $C_6H_6 + 3Cl_2 \xrightarrow{\text{Sunlight}} C_6H_6Cl_6$ $(BHC)$.
Therefore,the correct option is $(b)$.

(A) The full name of $DDT$ is $1,1,1-$trichloro$-2,2-$bis($p-$chlorophenyl)ethane.
It is a well-known organochlorine insecticide.
The structure consists of two $p-$chlorophenyl groups attached to a central carbon atom,which is also bonded to a trichloromethyl group $(CCl_3)$ and a hydrogen atom.

(B) The reaction between chlorobenzene and chloral $(CCl_3CHO)$ in the presence of concentrated $H_2SO_4$ leads to the formation of $DDT$ ($1,1,1$-trichloro-$2,2$-bis($p$-chlorophenyl)ethane).
The chemical reaction is:
$2C_6H_5Cl + CCl_3CHO \xrightarrow{conc. H_2SO_4} (ClC_6H_4)_2CHCCl_3 + H_2O$

(A) $D.D.T.$ (dichlorodiphenyltrichloroethane) is synthesized by the condensation reaction of chloral $(CCl_3CHO)$ with chlorobenzene in the presence of concentrated sulfuric acid.

(D) $DDT$ (dichlorodiphenyltrichloroethane) is prepared by the reaction of chlorobenzene with trichloroacetaldehyde (chloral) in the presence of concentrated $H_2SO_4$.
The reaction is: $2C_6H_5Cl + CCl_3CHO \xrightarrow{conc. H_2SO_4} (ClC_6H_4)_2CHCCl_3 + H_2O$.

(D) The term $ \text{war gas} $ often refers to $ \text{Chloropicrin} $ $( CCl_3NO_2 )$,which is prepared by the reaction of chloroform with nitric acid:
$ CHCl_3 + HNO_3 \to CCl_3NO_2 + H_2O $
Thus,the correct option is $ D $.

(C) Chloroform $(CHCl_3)$ is a colourless,sweet-smelling liquid that is almost insoluble in water. It is not highly inflammable; in fact,it is often used as a solvent in fire extinguishers. Historically,it was used as an inhalational anaesthetic,although its use has declined due to toxicity. Therefore,the statement that it is highly inflammable is false.

(C) Benzene hexachloride $(BHC)$ is a mixture of several stereoisomers of $1,2,3,4,5,6$-hexachlorocyclohexane formed by the light-induced addition of chlorine to benzene.
Among these isomers,the $\gamma$-isomer is known as lindane or gammexane,which acts as a very strong insecticide.

(B) Chloropicrin is chemically known as $CCl_3NO_2$.
It is also called Nitrochloroform.
It is prepared by the reaction of chloroform with concentrated nitric acid.

(D) $Chloroform$ $(CHCl_3)$ does not contain any $\pi$-unsaturation (double or triple bonds) and is not nucleophilic under standard conditions. Therefore,it does not undergo electrophilic addition with bromine $(Br_2)$ in the dark at room temperature. In contrast,$Propene$ and $Phenol$ readily react with bromine due to the presence of a double bond and an electron-rich aromatic ring,respectively. $Ethylamine$ can also react with bromine under specific conditions.

(A) $DDT$ (dichlorodiphenyltrichloroethane) is an organochlorine compound.
It is a synthetic chemical that does not occur naturally.
At room temperature,$DDT$ exists as a colorless,crystalline solid.

(C) $Hexachloroethane$ $(C_2Cl_6)$ is commonly used as a moth repellent. It has also been used as a plasticizer for cellulose esters,a polymer additive,a component of fungicidal and insecticidal formulations,and in the manufacture of fire extinguishing fluids.

(A) The chemical name $DDT$ stands for dichlorodiphenyl trichloroethane.
Its structure consists of two chlorophenyl groups attached to a central carbon atom,which is also bonded to a hydrogen atom and a trichloromethyl group $(CCl_3)$.
The correct formula is $(Cl-C_6H_4)_2CH-CCl_3$.

(A) The structure of $DDT$ (dichlorodiphenyltrichloroethane) is $CCl_3-CH(C_6H_4Cl)_2$.
In this structure,there are $3$ chlorine atoms in the $CCl_3$ group and $2$ chlorine atoms attached to the two benzene rings.
Therefore,the total number of chlorine atoms in $DDT$ is $3 + 2 = 5$.

(D) Chloropicrin,with the chemical formula $CCl_3NO_2$,is a chemical compound commonly used as a tear gas or riot control agent. It is also known as nitrotrichloromethane.

(A) $CCl_2F_2$ is known as Freon-$12$.
It is chemically named as dichloro difluoro methane.
It is a chlorofluorocarbon $(CFC)$ commonly used as a refrigerant in refrigerators and air conditioners.
Its release into the atmosphere causes ozone layer depletion.
Other examples of $CFCs$ include trichloro fluoro methane $(CCl_3F)$ and chloro difluoro methane $(CHClF_2)$.

(C) The given structure represents $1,1,1-\text{trichloro}-2,2-\text{bis}(p-\text{chlorophenyl})\text{ethane}$,which is commonly known as $DDT$.

(D) $CCl_4$ (carbon tetrachloride) is used in fire extinguishers.
Its vapours are non-inflammable and heavy,which helps in cutting off the oxygen supply to the fire.
It is commonly known as pyrene.

(B) $CCl_4$ is known as pyrene. It is stable to red heat and its vapours are non-inflammable,which makes it suitable for use as a fire extinguisher. However,its use is now restricted because,in the presence of water vapor,it can form the highly poisonous phosgene gas $(COCl_2)$. The reaction is: $CCl_4 + H_2O \to COCl_2 + 2HCl$.

(C) Mustard gas is prepared by the reaction of ethylene with sulfur dichloride $(SCl_2)$.
$2CH_2=CH_2 + SCl_2 \rightarrow ClCH_2CH_2-S-CH_2CH_2Cl$ (Mustard gas)

(A) $DDT$ stands for $p,p'$-dichlorodiphenyltrichloroethane.
The chemical structure of $DDT$ is $(ClC_6H_4)_2CHCCl_3$.
Counting the chlorine atoms: there are $2$ chlorine atoms on the benzene rings and $3$ chlorine atoms on the aliphatic carbon chain.
Total number of chlorine atoms $= 2 + 3 = 5$.

(D) $1$. The carbocation ${C}_{6}{H}_{5}-C{H}_{2}^{+}$ is a benzyl carbocation,which is stabilized by resonance with the benzene ring.
$2$. $A$ polyhalogenated compound contains more than one halogen atom in its structure.
$3$. $DDT$ (Dichlorodiphenyltrichloroethane) contains multiple chlorine atoms.
$4$. Chloropicrin $(CCl_{3}NO_{2})$ also contains multiple chlorine atoms.
$5$. Therefore,both $DDT$ and Chloropicrin are polyhalogenated compounds.

(B) Pyrene is the commercial name for carbon tetrachloride $(CCl_4)$.
It is used as a fire extinguisher,especially for electrical fires,because it is non-flammable and its vapors are heavy,which helps in cutting off the oxygen supply to the fire.

(B) $DDT$ stands for $p,p'$-dichlorodiphenyl trichloroethane.
It is a well-known organochlorine insecticide.
The structure consists of two chlorophenyl groups attached to a $1,1,1$-trichloroethane backbone.

(C) Carbon tetrachloride $(CCl_4)$ is used as a fire extinguisher. However,when it comes in contact with hot surfaces or water vapor at high temperatures,it undergoes a chemical reaction to produce phosgene $(COCl_2)$,which is a highly toxic gas. The reaction is: $CCl_4 + H_2O \rightarrow COCl_2 + 2HCl$. Therefore,proper ventilation is necessary to prevent the accumulation of this toxic gas.

(C) Westrosol is the common name for $1,1,2,2$-tetrachloroethene,which is also known as acetylene tetrachloride. Its chemical formula is $CHCl_2-CHCl_2$.

(C) $CCl_4$ (Carbon tetrachloride) is used as a fire extinguisher for fires involving oil,fats,and petrol.
It is commonly known by the trade name $Pyrene$.
It works by forming a heavy blanket of vapors over the fire,which cuts off the supply of oxygen.

(A) Iodoform $(CHI_3)$ is a yellow crystalline solid at room temperature. It has a characteristic antiseptic smell and is used as an antiseptic.

(D) $DDT$ (Dichlorodiphenyltrichloroethane) is prepared by the condensation reaction of chlorobenzene with trichloroacetaldehyde (chloral) in the presence of concentrated sulfuric acid $(H_2SO_4)$.
The reaction is: $2C_6H_5Cl + CCl_3CHO \xrightarrow{H_2SO_4} (ClC_6H_4)_2CHCCl_3 + H_2O$.

(B) Gammexane is the common name for the gamma isomer of benzene hexachloride $(B.H.C.)$,which is $1,2,3,4,5,6$-hexachlorocyclohexane. Its chemical formula is $C_6H_6Cl_6$. It is widely used as an insecticide.

(B) Gammexane is the common name for the gamma isomer of benzene hexachloride $(BHC)$,which is also known as lindane or $666$. Its chemical name is $1,2,3,4,5,6$-hexachlorocyclohexane.

(B) $DDT$ stands for $p,p'$-dichlorodiphenyltrichloroethane.
It is a well-known organochlorine insecticide.
The structure consists of two chlorophenyl groups attached to a central carbon atom,which is also bonded to a trichloromethyl group.

(D) The depletion of the ozone layer in the stratosphere is primarily caused by chlorofluorocarbons $(CFCs)$,commonly known as $Freons$.
These compounds release chlorine atoms in the presence of ultraviolet radiation,which then react with ozone $(O_3)$ to convert it into oxygen $(O_2)$,leading to the thinning of the ozone layer.

(C) Freons are chlorofluorocarbons (CFCs) used as refrigerants.
The most common Freon used in refrigerators is Freon-$12$,which is dichlorodifluoromethane,represented by the chemical formula $CCl_2F_2$.

(D) Chloropicrin,also known as trichloronitromethane,is formed by the reaction of chloroform with nitric acid.
Its chemical structure consists of a trichloromethyl group attached to a nitro group.
The molecular formula of chloropicrin is $CCl_3NO_2$.
Therefore,the correct option is $(D)$.

(D) Freons or chlorofluorocarbons $(CFCs)$ are responsible for the depletion of the ozone layer in the upper strata of the atmosphere.
They are used as propellants,aerosol spray caps,refrigerants,and fire-fighting reagents.
They are stable and chemically inert compounds that absorb $UV$ radiation and break down,liberating free atomic chlorine.
This chlorine atom causes the decomposition of ozone through a free radical reaction,resulting in the depletion of the ozone layer.
Common freons include $Freon-11$ $(CFCl_3)$ and $Freon-12$ $(CF_2Cl_2)$.
The reaction mechanism is as follows:
$Cl^{\bullet} + O_3 \longrightarrow ClO^{\bullet} + O_2$
$ClO^{\bullet} + O_3 \longrightarrow Cl^{\bullet} + 2O_2$

(D) Lindane,Gammexane,and $666$ are all common names for the same chemical compound,which is the $\gamma$-isomer of benzene hexachloride $(C_6H_6Cl_6)$.
$HCB$ stands for Hexachlorobenzene $(C_6Cl_6)$,which is a different chemical compound.
Therefore,$HCB$ is the odd one out.

(B) When two molecules of chlorobenzene react with one molecule of chloral $(CCl_3CHO)$ in the presence of concentrated $H_2SO_4$,they undergo a condensation reaction to form $1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane$,which is commonly known as $DDT$.
The reaction is as follows:
$2C_6H_5Cl + CCl_3CHO \xrightarrow{conc. H_2SO_4} (ClC_6H_4)_2CHCCl_3 + H_2O$
Thus,the correct option is $B$.

(D) $BHC$ stands for Benzene Hexachloride,which is $1,2,3,4,5,6$-hexachlorocyclohexane.
Its chemical formula is $C_6H_6Cl_6$.
In this structure,all carbon atoms are $sp^3$ hybridized and are connected by single bonds.
Therefore,there are no double bonds present in the molecule of $BHC$ (gammexane).

(B) $DDT$ ($p,p'-$dichlorodiphenyltrichloroethane) is a persistent organic pollutant. In the environment,it undergoes slow reductive dechlorination to form $DDD$ ($p,p'-$dichlorodiphenyldichloroethane). Therefore,the correct conversion product is $p,p'-$dichlorodiphenyldichloroethane.

(B) Chloropicrin is chemically known as trichloronitromethane.
Its chemical formula is $CCl_3NO_2$.
It is prepared by the reaction of chloroform with concentrated nitric acid.
Therefore,the correct option is $B$.

(D) Hexachloroethane $(C_2Cl_6)$ is known as artificial camphor.
It is used as a substitute for camphor in the manufacture of celluloid and as a moth repellent.

(D) $DDT$ (dichlorodiphenyltrichloroethane) is a persistent organic pollutant. In the environment,it undergoes slow degradation. The primary metabolic pathway involves the dehydrochlorination of $DDT$ to form $DDE$ ($p, p'-$ Dichlorodiphenyldichloroethene). This process is facilitated by microorganisms and environmental factors.

Organic compounds containing more than one halogen atom are known as polyhalogen compounds.
Examples of some polyhalogen compounds are:
$(i)$ Dichloromethane $(CH_{2}Cl_{2})$
$(ii)$ Trichloromethane/Chloroform $(CHCl_{3})$
$(iii)$ Triiodomethane/Iodoform $(CHI_{3})$
$(iv)$ Tetrachloromethane/Carbon tetrachloride $(CCl_{4})$
$(v)$ Freons (chlorofluorocarbons of methane and ethane),Freon-$12$ $(CCl_{2}F_{2})$
$(vi)$ $p,p'-$Dichlorodiphenyltrichloroethane $(DDT)$,$CCl_{3}CH(p-C_{6}H_{4}Cl)_{2}$

(N/A) Uses of Chloroform:
It is used as a solvent for fats,alkaloids,iodine,and other substances. Currently,its major use is in the production of the freon refrigerant $R-22$.
Previously,it was used as a general anesthetic in surgery,but it has been replaced by safer and less toxic anesthetics like ether.
$(b)$ Harmful Effects of Chloroform:
Chloroform is an anesthetic; inhaling its vapors depresses the central nervous system.
Inhalation of air containing $900$ parts per million $(ppm)$ of chloroform for a short time can cause dizziness,fatigue,and headache.
Chronic exposure to chloroform can damage the liver and kidneys (it is metabolized to phosgene in the liver).
Direct skin contact with chloroform can cause sores.
$(c)$ Storage of Chloroform:
Chloroform is stored in dark-colored bottles because it is slowly oxidized by air $(O_2)$ in the presence of light to form the highly poisonous gas carbonyl chloride ($COCl_2$,phosgene).
To prevent this,it is stored in dark-colored bottles filled to the brim.
$2CHCl_3 + O_2 \rightarrow 2COCl_2 + 2HCl$
Phosgene $(COCl_2)$ is a toxic gas that causes damage to the liver and kidneys.

(N/A) Uses of carbon tetrachloride:
It is produced in large quantities for use in the manufacture of refrigerants and propellants for aerosol cans.
It is used as a raw material for the synthesis of chlorofluorocarbons and other chemicals.
Until the mid-$1960$s,it was widely used as a cleaning fluid for grease,a spot remover in homes,and as a fire extinguisher.
$(b)$ Harmful effects of carbon tetrachloride:
Exposure to carbon tetrachloride causes liver cancer in humans.
It causes dizziness,lightheadedness,nausea,and vomiting,which leads to permanent damage to nerve cells.
Severe exposure can cause stupor,coma,and death.
When released into the air,it reaches the atmosphere and depletes the ozone layer.
Depletion of the ozone layer increases human exposure to ultraviolet rays,leading to skin cancer,eye diseases,and disorders,and potential disruption of the immune system.