Text Book Back Questions and Answers - Chapter 14 Haloalkanes and Haloarenes 11th Chemistry Guide Samacheer Kalvi Solutions - SaraNextGen [2024-2025]

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On April 24, 2024, 11:35 AM

Haloalkanes and Haloarenes
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Multiple Choice Questions
Question 1.
The IUPAC name of

(a) 2-Bromopent-3-ene
(b) 4-Bromopent - 2-ene
(c) 2-Bromopent - 4-ene
(d) 4-Bromopent - 1 - ene
Answer:
(b) 4-Bromopent-2-ene
Question 2.
Of the following compounds. which has the highest boiling point'?
(a) n-Butyl chloride
(b) Isobutyl chloride
(c) t-Butyl chloride
(d) n-propyl chloride
Answer:
(a) n-Butyl chloride
Question 3.
Arrange the following compounds in increasing order of their density.
(A) $\mathrm{CCl}_4$
(B) $\mathrm{CHCl}_3$
(C) $\mathrm{CH}_2 \mathrm{Cl}_2$
(D) $\mathrm{CH}_3 \mathrm{Cl}$
(a) D $<$ C $<$ B $<$ A
(b) $\mathrm{C}<$ B $<$ A $<$ D
(c) A $<$ B $<\mathrm{C}<\mathrm{D}$
(d) $\mathrm{C}<$ A $<$ B $<$ D
Answer:
(a) D $<$ C $<$ B $<$ A
Question 4.
With respect to the position of $-\mathrm{Cl}$ in the compound $\mathrm{CH}_3-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_2-\mathrm{Cl}$, it is classified as ......................

(a) Vinyl
(b) Allyl
(c) Secondary
(d) Aralkyl
Answer:
(b) Allyl
Question 5 .
What should be the correct IUPAC name of diethyl chioromethane?
(a) 3-Chioropentane
(b) 1-Chloropentane
(c) 1-Chloro- 1, 1, diethylmethanc
(d) 1-Chloro- 1 -ethylpropane
Answer:
(a) 3-Chioropentane
Question 6.
$\mathrm{C}-\mathrm{X}$ bond is strongest in
(a) Chioromeihane
(b) lodomethane
(c) Bromomethane
(d) Fluoromethanc
Answer:
(d) Fluoromethane
Question 7.

In the reaction   $\mathrm{X}+\mathrm{N}_2, \mathrm{X} \text { is .. }$

Answer:

Question 8 .
Which of the following compounds will give racemic mixture on nucleophilic substitution by $\mathrm{OH}^{-}$ion?

(a) (i)
(b) (ii) and (iii)
(c) (iii)
(d) (i) and (ii)
Answer:
(c) (iii)
Question 9.
The treatment of ethyl formate with excess of $\mathrm{RMgX}$ gives -

Answer:
(c) $\mathrm{R}-\mathrm{CHO}$
Question 10 .
Benzene reacts with $\mathrm{Cl}_2$ in the presence of $\mathrm{FeCl}_2$ and in absence of sunlight to form -
(a) Chiorobenzene
(b) Benzyl chloride
(c) Benzal chloride
(d) Benzene hexachloride
Answer:
(a) Chiorobenzene
Question 11 .
The name of $\mathrm{C}_2 \mathrm{~F}_4 \mathrm{Cl}_2$ is -
(a) Freon - 112
(b) Freon - 113
(c) Freon - 114
(d) Freon - 115
Answer:
(c) Freon -114
Question 12 .
Which of the following reagent is helpful to differentiate ethylene dichloride and ethylidene chloride?
(a) $\mathrm{Zn} /$ methanol
(b) $\mathrm{KOH} /$ ethanol
(c) Aqueous $\mathrm{KOH}$
(d) $\mathrm{ZnCl}_2 /$ Cone. $\mathrm{HCl}$
Answer:
(e) Aqueous $\mathrm{KOH}$
Question 13.
Match the compounds given in Column I with suitable items given in Column II.
Answer:

Code:
(a) $\mathrm{A} \rightarrow 2, \mathrm{~B} \rightarrow 4, \mathrm{C} \rightarrow 1, \mathrm{D} \rightarrow 3$
(b) $\mathrm{A} \rightarrow 3, \mathrm{~B} \rightarrow 2, \mathrm{C} \rightarrow 4, \mathrm{D} \rightarrow 1$
(c) $\mathrm{A} \rightarrow 1, \mathrm{~B} \rightarrow 2, \mathrm{C} \rightarrow 3, \mathrm{D} \rightarrow 4$
(d) $\mathrm{A} \rightarrow 3, \mathrm{~B} \rightarrow 1, \mathrm{C} \rightarrow 4, \mathrm{D} \rightarrow 2$
Answer:
(d) $\mathrm{A} \rightarrow 3, \mathrm{~B} \rightarrow 1, \mathrm{C} \rightarrow 4, \mathrm{D} \rightarrow 2$
Question 14.
Assertion : in monohaloarenes, electrophilic substitution occurs at oriho and para positions.
Reason : Halogen atom is a ring deactivator.
(a) If both assertion and reason arc true and reason is the correct explanation of assertion.
(b) If both assertion and reason are true but reason is not the correct explanation of assertion.
(c) If assertion is true but reason is false.
(d) If both assertion and reason are false.
Answer:
(b) If both assertion and reason are true but reason is not the correct explanation of assertion.
Question 15 .
Consider the reaction, $\mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{Br}+\mathrm{NaCN} \rightarrow \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{CH}_2 \mathrm{CN}+\mathrm{NaBr}$ This reaction will be the fastest in
(a) ethanol
(b) methanol
(c) DMF (N, N'-dimethyl forrnamide)
(d) water
Answer:
(c) DMF (N, N'-dimethyl fonuarnide)
Question 16.
Freon-12 is manufactured from tetrachioromethane by
(a) Wurtz reaction
(b) Swarts reaction
(c) DMF (N, N'-dimethyl tòrmamide)
(d) water
Answer:
(c) DMF (N, N'-dimethyl formarnide)

Question 16.
Frcon-12 is manufactured from tetrachioromethane by
(a) Wurtz reaction
(b) Swans reaction
(c) Haloform reaction
(d) Gattennann reaction
Answer:
(b) Swarts reaction
Question 17.
The most easily hydrolysed molecule under $\mathrm{S}_{\mathrm{N}^1}$ condition is
(a) allyl chloride
(b) ethyl chloride
(c) isopropyl chloride
(d) benzyl chloride
Answer:
(a) benzyl chloride
Question 18.
The carbocation formed in $\mathrm{S}_{\mathrm{N}^1}$ reaction of alkyl halide in the slow step is
(a) $\mathrm{sp}^3$ hybridised
(b) $\mathrm{sp}^2$ hybridised
(c) $s p$ hybridised
(d) none of these
Answer:
(b) $\mathrm{sp}^2$ hybridised
Question 19.
The major products obtained when chiorobenzene is nitrated with $\mathrm{HNO}_3$ and cone. $\mathrm{H}_2 \mathrm{SO}_4$
(a) 1-chloro-4-nitrobenzenc
(b) 1-chloro-2-n itrobenzene
(c) 1-chloro-3-n itroberizene
(d) 1-chloro- 1 -nitrobenzene
Answer:
(a) 1 -chloro-4-nitrobenzene

Question 20 .
Which one of the following is most reactive towards nucleophilic substitution reaction?

Answer:

Question 21.
Ethylidene chloride on treatment with aqueous $\mathrm{KOH}$ gives
(a) acetaldehyde
(b) ehtylene glycol
(c) formaldehyde
(d) glyoxal
Answer:
(a) acetaldehyde
Question 22.
The raw material for Rasching process is
(a) chiorobenzene
(b) phenol
(c) benzene
(d) anisole
Answer:
(c) benzene
Question 23.
Chloroform reacts with nitric acid to produce
(a) nitro-toluene
(b) nitro-glycerine
(c) chloropicrin
(d) chioropicric acid
Answer:
(c) chioropicrin

Question 24
Acetone $\frac{\text { (i) } \mathrm{CH}_3 \mathrm{MgI}}{\left(\text { ii )} \mathrm{H}_2 \mathrm{O} / \mathrm{H}^{-1}\right.} \mathrm{X}, \mathrm{X}$ is
(a) 2-propanol
(b) 2-methyl-2-propanol
(c) 1 -propanol
(d) acetonol
Answer:
(b) 2-methyl-2-propanol
Question 25 .
Silver propionate when refluxed with Bromine in carbon tetrachioride gives
(a) propionic acid
(b) chioroethane
(c) bromoethane
(d) chioropropane
Answer:
(c) bromoethane
Short Answer Questions
Question 26.
Classify the following compounds in the form of alkyl. allylic, vinyl, benzylic halides:
(a) $\mathrm{CH}_3-\mathrm{CH}=\mathrm{CH}-\mathrm{Cl}$
(b) $\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}_2 \mathrm{I}$

(c) 

(d) $\mathrm{CH}_2=\mathrm{CH}-\mathrm{Cl}$
Answer:
(a) $\mathrm{CH}_3-\mathrm{CH}=\mathrm{CH}-\mathrm{Cl}$ - Allylic halide
(b) $\mathrm{C}_6 \mathrm{H}_5 \mathrm{CH}_2-$ Benzylic halide

(c)

(d) $\mathrm{CH}_2=\mathrm{CHCl}-$ Vinyl halide
Question 27.
Why chlorination of methane is not possible in dark?
Answer:
- Chlorination of methane is a free radical substitution reaction.
- Before chlorine reacts with methane, the $\mathrm{Cl}-\mathrm{Cl}$ single bond must break to form free radicals and this can only be done in the presence of ultraviolet light.
- In dark, chlorine free radicals formation is not possible and so chlorination of methane is not possible in dark.
- The ultraviolet light is a source of energy and it being used to break of $\mathrm{Cl} \mathrm{Cl}$ and produce $\mathrm{Cl}$ free radical Free radical's which can attack methane. in dark this is not possible.
Question 28.
How will you prepare n-propyl iodide from $\mathrm{n}$-propyl bromide?
Answer:
Finkeistein reaction:
n-propyl bromide on heating with a concentrated solution of sodium iodide in dry acetone gives $\mathrm{n}$-propyl iodide. This $\mathrm{S}_{\mathrm{N}^2}$ reaction is called Finkelstein reaction.

Question 29 .
Which alkyl halide from the following pair is -
1. chiral
2. undergoes faster $\mathrm{S}_{\mathrm{N}^2}$ reaction?

Answer:

1. 

$\text { Here the } \mathrm{C}^* \text { is chiral carbon atom and it is surrounded by four different groups. }$

2. 

$\mathrm{Cl}_{\text {i.e., 1-chiorohutane undergoes faster }} \mathrm{S}_{\mathrm{N}^2}$ reaction. $\mathrm{CH}_3-\mathrm{CH}_2-\mathrm{CH}_2 \mathrm{Cl}$ is a primary alkyl halide and so it undergoes faster $\mathrm{S}_{\mathrm{N}^2}$ reaction.
Question 30.
How does chiorobenzene react with sodium in the presence of ether? What is the name of the reaction?
Answer:
Chiorobenzene when heated with sodium in ether solution will forrn biphenyl as the product. This reaction is called fitting reaction.

Question 31.
Give reasons for polarity of $\mathrm{C}-\mathrm{X}$ bond in haloalkancs.
Answer:
- Carbon halogen bond is a polar bond as halogens are more electronegative than carbon.
- The carbon atom exhibits a partial positive change $\left(\delta^{+}\right)$and halogen atom acquires a partial negative change. $\left(\delta^{-}\right)$

Question 32.
Why is it necessary to avoid even traces of moisture during the use of Grignard reagent?

Answer:
Grignard reagents are highly reactive substances. They react with any source of proton to form hydrocarbons. Even water is sufficiently acidic to convert it into the corresponding hydrocarbon. So it is necessary to avoid even traces of moisture with the Grignard reagent as they arc highly reactive.

Question 33.
What happens when acetyl chloride is treated with excess of $\mathrm{CH}_3 \mathrm{MgI}$ ?
Answer:
When acetyl chloride is treated with excess of Grignard reagent, the product formed is tertiary butyl alcohol.

Question 34.
Arrange the following alkyl halideïniiicreasing order of bond enthalpy of $\mathrm{RX}: \mathrm{CH}_3 \mathrm{Br}, \mathrm{CH}_3 \mathrm{~F}, \mathrm{CH}_3 \mathrm{Cl}$,
$\mathrm{CH}_3 \mathrm{I}$
Answer:
increasing order of bond enthalpy of $\mathrm{RX}$ is
$\mathrm{CH}_3 \mathrm{I}$ bond enthalpy $234 \mathrm{~kJ} \mathrm{~mol}^{-1}$
$\mathrm{CH}_3 \mathrm{Br}$ bond enthalpy $293 \mathrm{~kJ} \mathrm{~mol}^{-1}$
$\mathrm{CH}_3 \mathrm{Cl}$ bond enthalpy $351 \mathrm{~kJ} \mathrm{~mol}^{-1}$
$\mathrm{CH}_3 \mathrm{~F}$ bond enthalpy $452 \mathrm{IcI} \mathrm{mol}{ }^{-1}$
$\mathrm{CH}_3 \mathrm{~F}>\mathrm{CH}_3 \mathrm{Cl}>\mathrm{CH}_3 \mathrm{Br}<\mathrm{CH}_3 \mathrm{I}$
Question 35.
What happens when chloroform reacts with oxygen in the presence of sunlight?
Answer:
Chloroform undergoes oxidation in the presence of sunlight and air to form phosgene (carboxyl chloride)

Since phosgene is very poisonous, therefore its presence makes chloroform unfit for use as anaesthetic.
Question 36.
Write down the possible isomers of $\mathrm{C}_5 \mathrm{H}_{11} \mathrm{Br}$ and give their IUPAC and common names.
Answer:
$\mathrm{C}_5 \mathrm{H}_{11} \mathrm{Br}: 8$ isomers are possible.

Question 37.
Mention any three methods of preparation of haloalkanes from alcohols.
Haloalkanes are prepared from alcohols by treating with -
1. $\mathrm{HCl}$
2. $\mathrm{PCl}_5$
3. $\mathrm{SO}_2 \mathrm{Cl}_2$
Answer:
1. Reaction of alcohol with hydrogen halide:

2. Reaction of alcohol with phosphorous halide: 

3. Reaction of alcohol with thionyl chloride: 

Question 38.
Compare $\mathrm{S}_{\mathrm{N}^1}$ and $\mathrm{S}_{\mathrm{N}^2}$ reaction mechanisms.
Answer:
$\mathrm{S}_{\mathrm{N}^1}$ Mechanism:
1. It is a unimolecular nucleophilic substitution reaction of first order.
2. It takes place in two steps.
3. It leads to racemisation.
4. It mostly take place in tertiary alkyl halides.
5. The rate of the reaction depends only on the concentration one of substrate and so it is a first order reaction.
Step - I

Step II

$\mathrm{S}_{\mathrm{N}^2}$ Mechanism:
1. It is a bimolecular nucleophilic substitution reaction of second order.
2. It takes place in one step.
3. It leads to invertion of configuration.
4. It mostly take place in primary alkyl halides.
5. The rate of the reaction depends on the concentration of both the substrate as well as the nucleophile and so it is a second order reaction.

Question 39 .
Compare $\mathrm{S}_{\mathrm{N}^1}$ and $\mathrm{S}_{\mathrm{N}^2}$ reaction mechanisms.

Answer:

Question 40 .
Discuss the aromatic nucicophilic substitution reactions of chiorobenzene.
Answer:
Aromatic nucleophilic substitution reactions:
Dow's process:

Question 41.
Account for the following -
1. t-butyl chloride reacts with aqueous $\mathrm{KOH}$ by $\mathrm{S}_{\mathrm{N}}{ }^1$ mechanism while n-butyl chloride reacts with $\mathrm{S}_{\mathrm{N}^2} \text { mechanism. }$
2. p-dichlorobenzene has higher melting point than those of o-and m-dichlorobenzene.
Answer:
1. In t-butyl chloride, there is niore steric hindrance and it involves formation of a stable tertiary carbocation. Therefore it reacts with $\mathrm{KOH}$ by $\mathrm{S}_{\mathrm{N}^1}$ mechanism rather than $\mathrm{S}_{\mathrm{N}^2}$ mechanism because $\mathrm{S}_{\mathrm{N}^1}$ mechanism is faourable in case of steric crowding and is directly proportional to partial positive charge on carbon atom. In n-butyl chloride, there is least steric hindrance and involves formation of less stable primary carbocation. Thus it takes place in one step and is favoured by $\mathrm{S}_{\mathrm{N}^2}$ mechanism.

2. Melting point of $\mathrm{p}$-dichiorobenzene is higher than that of ortho and meta-dichiorobenzene. This is due to the fact that is has a symmetrical structure and therefore, its molecules can easily pack closely in the crystal lattice. p-dichlorobcnzene being more symmetrical fits closely in the crystal lattice and has stronger intermolecular attraction than o $\& \mathrm{~m}$ isomers. So p-isomer has high melting point than the corresponding o \& $\mathrm{m}$-isomers.
Question 42.
In an experiment ethyliodide in ether is allowed to stand over magnesium pieces. Magnesium dissolves and product is formed
(a) Name the product and write the equation for the reaction.
(b) Why all the reagents used in the reaction should be dry? Explain.
(c) How is acetone prepared from the product obtained in the experiment?
Answer:
(a) When ethyl iodide in ether is allowed to stand over magnesium pieces. the product formed will be Ethyl magnesium iodide.

(b) Gngnard reagent are highly reactive compounds and react with any source of proton to give hydrocarbons. Even when water is there, it is sufficiently acidic to convert it into the corresponding hydrocarbon. So it is necessary to avoid even traces of moisture with the grignard reagent as they are highly reactive. That is why the all reagents used in the reaction should be dry.

(c)

Methyl magnesium iodide reacts with acetyl chloride to form acetone. 

Question 43.
Write a chemical reaction useful to prepare the following:
1. Freon- 12 from carbon tetrachioride.
2. Carbon tetrachioride from carbon disulphide.
Answer:
1. Freon-12 from carbon tetrachioride:
Freon- 12 is prepared by the action of hydrogen fluoride on carbon tetrachioride in the presence of catalytic amount of antimony pentachloride. This is called "swartz reaction".

2. Carbon tetrachioride from carbon disuiphide:
Carbon disuiphide reacts with chlorine gas in the presence ofanhydrous $\mathrm{AlCl}_3$ as catalyst to give carbon tetrachloridc.

Question 44.
What are Freons? Discuss their uses and environmental effects.
Answer:
Freons are the chiorofluoro derivatives of methane and ethane.
Freon is represented as Freon - cba
Where, $\mathrm{c}=$ number of carbon atoms, $\mathrm{b}=$ number of hydrogen atoms, $a=$ total number of fluorine atoms.
$\mathrm{CF}_2 \mathrm{Cl}_2=0$
$\mathrm{c}=1-1=0$
$\mathrm{H}=0+1=1$
$\mathrm{F}=2$
So Freon -12 is $\mathrm{CF}_2 \mathrm{Cl}_2$
Uses of Freons:
- Freons are used as refrigerants in refrigerators and air conditioners.
- it is used as a propellant for aerosols and foams.
- it is used as propellant for foams to spray out deodorants, shaving creams and insecticides.
Environmental effects of Freons:
1. Freon gas is a very powerful greenhouse gas which means that it traps the heat normally radiated from the earth out into the space. This causes the earth's temperature to increase, resulting in rising sea levels, droughts. stronger storms, flash floods and a host of other very unpleasant effect.
2. As freon moves throughout the air, its chemical ingredients causes depletion of ozone layer. Depletion of ozone increases the amount of ultraviolet radiations that reaches the earths surface, resulting in serious risk to human health. High levels of ozone, in turn, causes resoiratory problems and can also kill olants.
Question 45.
Predict the products when bromoethane is treated with the fòllowing:
1. $\mathrm{KNO}_2$
2. $\mathrm{AgNO}_2$
Answer:
1. When bromoethane is treated with $\mathrm{KNO}_2$ the product formed is Ethyl nitrite.

$\text { 2. When bromoethane is treated with } \mathrm{AgNO}_2 \text { nitroethane will be formed as the product. }$

Question 46.
Explain the mechanism of $\mathrm{S}_{\mathrm{N}^1}$ reaction by highlighting the stereochemistry behind it.
Answer:
1. $\mathrm{S}_{\mathrm{N}^1}$ stands for unimolecular nucleophilic substitution reaction of first order reaction.
2. The rate of the following $S_{N^1}$ reaction depends upon the concentration of alkyl halide
(RX) and it is independent of the concentration of the nucicophile $\left(\mathrm{OH}^{-}\right)$used.
3. $\mathrm{R}-\mathrm{Cl}+\mathrm{OH}^{-} \mathrm{R}-\mathrm{OH}+\mathrm{Cl}^{-}$
4. This $S_{\mathrm{N}^1}$ reaction follows first order kinetics and it occurs in two steps:

$\text { 5. } S_{N^1} \text { reaction mechanism takes place in tertiary butyl bromide with aqueous } \mathrm{KOH} \text { a follows: }$

6. the 2 steps of the reaction are:
Step 1:
Formation of carbocation:
The polar $\mathrm{C}-\mathrm{Br}$ bond breaks first forming a carbocation and bromide ion. This step is slow and hence it is the rate determining step.

The carbocation has two equivalent lobes of the vaccant $2 p$ orbital, So it can react equally fast form either face.
Step 2:
The nucleophile immediately reacts with the carbocation. This step is fast and hence does not affect the rate of the reaction.

The nucleophile $\mathrm{OH}$ can attack carbocation from both the sides.
Question 47.
Write short notes on the the following:
1. Raschig process
2. Dows Process
3. Darzens process
Answer:
1. Raschig process:
Chiorobenzene is commercially prepared by passing a mixture of benzene vapour in air and $\mathrm{HUt}$ over heated cupric chloride.

2. Dow's process:
Chiorobenzene is boiled with Sodium hydroxide to get Phenol. This reaction is called Dow's process.

3. Darzens process:
Ethanol reacts with $\mathrm{SOCl}$, in the presence of pyridine to form chloroethane. This reaction is called Darzens process.

Question 48.
Starting from $\mathrm{CH}_3 \mathrm{MgI}$. How will you prepare the following'?
1. Acetic acid
2. Acetone
3. Ethyl acetate
4. Isopropyl alcohol
5. Methyl cyanide
Answer:
1. Acetic acid from grignard reagent:

2. Acetone from Gngnard reagent: 

3. Ethyl acetate from Grignard reagent: 

4. Isopropyl alcohol from Grignard reagent: 

5. Methyl cyanide form Grignard reagent: 

Question 49.
Complete the following reactions:
1. $\mathrm{CH}_3-\mathrm{CH}=\mathrm{CH}_2+\mathrm{HBr} \stackrel{\text { Peroxide }}{\longrightarrow}$
2. $\mathrm{CH}_3-\mathrm{CH}_2-\mathrm{Br}+\mathrm{NaSH} \stackrel{\text { Alcohol }}{\underset{\mathrm{H}_2 \mathrm{O}}{\longrightarrow}}$
3. $\mathrm{C}_6 \mathrm{H}_5 \mathrm{Cl}+\mathrm{Mg} \stackrel{\mathrm{THF}}{\longrightarrow}$

$\text { 4. } \mathrm{CHCl}_3+\mathrm{HNO}_3 \stackrel{\Delta}{\longrightarrow}$
5. $\mathrm{CCl}_4+\mathrm{H}_2 \mathrm{O} \stackrel{\Delta}{\longrightarrow}$

Answer:

1. 

2.

3.

4. 

5. 

Question 50.
Explain the preparation of the following compounds:
1. DDT
2. Chloroform
3. Biphenyl
4. Chioropicrin
5. Freon-12
Answer:
1. DUT

2. Chloroform:

3. Biphenyl:
Fittig reaction:

4. Chioropicrin.

5. Freon -12

Question 51 .
An organic compound (A) with molecular formula $\mathrm{C}_2 \mathrm{H}_5 \mathrm{Cl}$ reacts with $\mathrm{KOH}$ gives compounds (B) and with alcoholic $\mathrm{KOH}$ gives compound (C). Identify (A), (B) and (C)
Answer:

1. An organic compound (A) of molecular formula $\mathrm{C}_2 \mathrm{H}_5 \mathrm{Cl}$ is identified as Chioroethane with molecular formula $\mathrm{CH}_2-\mathrm{CH}_2 \mathrm{Cl}$ from the formula.
2. Chioroethane reacts with aqueous $\mathrm{KOH}$ to give ethanol, i.e., Aqueous $\mathrm{C}_2 \mathrm{H}_5 \mathrm{OH}$ as (B) by substitution reaction.

$\text { 3. ChIooethane reacts with alcoholic } \mathrm{KOH} \text { to give ethene } \mathrm{C}_2 \mathrm{H}_4 \text { as (C) by elimination reaction. }$

Question 52.
Simplest alkene (A) reacts with $\mathrm{HCl}$ to form compound (B). Compound (B) reacts with ammonia to form compound $(\mathrm{C})$ of molecular formula $\mathrm{C}_2 \mathrm{H}_2 \mathrm{~N}$. Compound (C) undergoes carbylarnine test. Identify (A),
(B), and (C).
Answer:

1. The simplest alkene (A) is $\mathrm{CH}_2=\mathrm{CH}_2$, ethene.
2. Ethene reacts with $\mathrm{HCl}$ to give Chioroethane $\mathrm{CH}_2-\mathrm{CH}_2 \mathrm{Cl}$ as (B) by addition reaction.

3. Chioroethane reacts with ammonia to give Ethylamine $\mathrm{CH}_3-\mathrm{CH}_2 \mathrm{NH}_2$ as (C). It is a primary amine and Carbylamine test is the characteristic test for $1^{\circ}$ amine.

Question 53.
A hydrocarbon $\mathrm{C}_3 \mathrm{H}_6$ (A) reacts with $\mathrm{HBr}$ to form compound (B). Compound (B) reacts with aqueous potassium hydroxide to give (C) of molecular formula $\mathrm{C}_3 \mathrm{H}_8 \mathrm{O}$. What are (A) (B) and (C). Explain the reactions.
Answer:

1. The hydrocarbon with molecular formula $\mathrm{C}_3 \mathrm{H}_6$ (A) is identified as propene, $\mathrm{CH}_3-\mathrm{CH}=\mathrm{CH}_2$
2. Propene reacts with $\mathrm{HBr}$ to form brornopropane $\mathrm{CH}_3-\mathrm{CH}_2-\mathrm{CH}_2 \mathrm{Br}$ as (B).

3. 1 -bromopropanc react with aqueous potassium hydroxide to give 1 -propanol $\mathrm{CH}_3-\mathrm{CH}_2 \mathrm{CH}_2 \mathrm{OH}$ as (C).
4. 2-bromo propane reacts with aqueous $\mathrm{KOH}$ to give 2-propanol as (C)

Question 54.
Two isomers (A) and (B) have the same molecular formula $\mathrm{C}_2 \mathrm{H}_4 \mathrm{Cl}_2$. Compound (A) reacts with aqueous $\mathrm{KOK}$, gives compound (C) of molecular formula $\mathrm{C}_2 \mathrm{H}_4 \mathrm{O}$. Compound (B) reacts with aqueous $\mathrm{KOH}$, gives compound (D) of molecular formula $\mathrm{C}_2 \mathrm{H}_6 \mathrm{O}_2$. Identif' (A), (B), (C) and (D).
Answer:

1. The compounds (A) and (B) with the molecular formula $\mathrm{C}_2 \mathrm{H}_4 \mathrm{Cl}_2$ are
 and  respectively with IUPAC names: 1, 1-dichloroethane (A) and 1.
2. 1, 1-dichloroethane reacts with aqueous $\mathrm{KOH}$ tp give $\mathrm{CH}_3 \mathrm{CHO}$ Acetaldehyde as (C).

3. 1,2-dichloroethane reacts with aqueous $\mathrm{KOH}$ to give ethylene glycol
 as (D).

Question 1.
Write the IUPAC name of the following:

(i) 

(ii)

(iii)

Answer:

(i)

(ii)

(iii)

Question 2 .
Write the structure of the following compounds:
1. 1-Bromo-4-cthylcyclo hexane
2. 14-Dichlorobut-2-ene
3. 2 Chloro-3-methyl pentane
Answer:
1. 1-Bromo-4 ethylcyclo hexane

2. 1. 4-Dichioro but-2-ene 

3. 2-Çhloro-3-methyl pentane 

Question 3.
Write all possible chain isomers with molecular formula $\mathrm{C}_5 \mathrm{H}_{11} \mathrm{Cl}$
Answer:
$\mathrm{C}_5 \mathrm{H}_{11} \mathrm{Cl}$ :
8 isomers arc possible. These are -

Question 4.
neo-pentyl bromide undergoes nucleophilic substitution reactions very slowly. Justify.
Answer:

1. 

neo-pentyl bromide undergoes nucleophilic substitution reactions very slowly due to steric hindrance of many alkyl groups. When bromide is attached to neo-pentyl carbon atom, the heterolytic cleavage of $\mathrm{C}-\mathrm{Br}$ takes place very slowly and substitution is also a very slow reaction.
2. Due to bulky neo-pentyl group, it becomes difficult for a nucleophile to attack from the back side of carbon having $\mathrm{C}-\mathrm{Br}$ bond.
3. Splitting of $\mathrm{C}-\mathrm{Br}$ gives a primary carbocation which is very less stable. So neo-pentyl bromide undergoes nucleophilic substitution reactions very slowly.
Question 5.
Why Grignard reagent should be prepared in anhydrous condition'?

Answer:

Grignard reagent are highly reactive species and react with any source of proton to give hydrocarbons. Even when water is there, it is sufficiently acidic to convert it into the corresponding hydrocarbon. So it is necessary to avoid even traces of moisture while preparing grignard reagent as they are highly reactive and that is why gngnard reagent should be prepared in anhydrous conditions.
Question 6.
Haloalkanes undergo nucleophilic substitution reaction whereas haloarenes undergo electrophilic substitution reaction. Comment.
Answer:
Haloalkanes undergo nucleophilic substitution reactions due to high clectronegativity of the halogen atom. The $\mathrm{C}-\mathrm{X}$ bond in haloalkanes is slightly polar, thereby the $\mathrm{C}$ atom acquires a slight positive charge in $\mathrm{C}-\mathrm{X}$ bond. [lence $\mathrm{C}$ atom is a good target for attack for nucleophiles. Therefore $\mathrm{C}-\mathrm{X}$ atom of haloalkanes is replaced by a nucleophile easily.

On the other hand in haloarenes, the halogen atom releases electron to the benzene nucleus relatively electron rich with respect to the halogen atom. As a result the electrophilic attack occurs at ortho and para positions. Hence haloarenes undergo electrophilic substitution reactions.
Question 7.
Chloroform is kept with a little ethyl alcohol in a dark coloured bottle. Why?
Answer:
1. Chlorofòrm is slowly oxidised by air in the presence of light to an extremely poisonous gas, carboxyl chloride (phosgene). it is therefore stored in closed dark coloured bottles completely filled so that air is kept out.
2. With the use of $1 \%$ ethanol we can stabilise chloroform, because ethanol can convert the poisonous $\mathrm{COCl}_2$ gas into non poisonous diethyl carbonate.
$
\mathrm{COCl}_2+2 \mathrm{C}_2 \mathrm{H}_5 \mathrm{OH} \mathrm{CO}\left(\mathrm{OC}_2 \mathrm{H}_5\right)_2+2 \mathrm{HCl}
$

Question 8.
What is the IUPAC name of the insecticide DDT? Why is their use banned in most of the countries?
Answer:
1. The IUPAC name of the insecticide DDT isp, p-dichloro-diphenyl trichioroethane.
2. Even DDT is an effective insecticide. Now-adays it is banned because of its long term toxic effects.
3. DDT is very persistent in the environment and it has a high affinity for fatty tissues. As a result, DDT gets accumulated in animal tissue fat, in particular that of birds of prey with subsequent thinning of their eggs shells and impacting their rate of reproduction. That is why DDT is banned in most of the countries.