Samacheer Kalvi 11th Chemistry Guide Chapter 14 Haloalkanes and Haloarenes

Tamilnadu State Board New Syllabus Samacheer Kalvi 11th Chemistry Guide Pdf Chapter 14 Haloalkanes and Haloarenes Text Book Back Questions and Answers, Notes.

Tamilnadu Samacheer Kalvi 11th Chemistry Solutions Chapter 14 Haloalkanes and Haloarenes

11th Chemistry Guide Haloalkanes and Haloarenes Text Book Back Questions and Answers

Textbook Evaluation:

I. Choose the best answer:

Question 1.
The IUPAC name of is
a) 2 – Bromo pent – 3 – ene
b) 4 – Bromo pent – 2 – ene
c) 2 – Bromo pent – 4 – ene
d) 4 – Bromo pent – 1 – ene
Answer:
b) 4 – Bromo pent – 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) CCl₄
B) CHCl₃
C) CH₂Cl₂
D) CH₃Cl
a) D < C < B < A
b) C > B > A > D
c) A < B < C < D
d) C > A > B > D
Answer:
a) D < C < B < A

Question 4.
With respect to the position of – Cl in the compound CH3 – CH = CH – CH₂ – 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 chloromethane?
a) 3 – Chloro pentane
b) 1 – Chloropentane
c) 1 – Chloro – 1, 1 – diethyl methane
d) 1- Chloro-1-ethyl propane
Answer:
a) 3 – Chloro pentane

Question 6.
C – X bond is strongest in
a) Chloromethane
b) Iodomethane
c) Bromomethane
d) Fluoromethane
Answer:
d) Fluoromethane

Question 7.
In the reaction X is ______.

Answer:
b)

Question 8.
Which of the following compounds will give racemic mixture on nucleophilic substitution by OH^– ion?
i)

ii)

iii)
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 RMgX gives
a)

b)
c) R – CHO
d) R – O – R
Answer:
c) R – CHO

Question 10.
Benzene reacts with Cl₂ in the presence of FeCl₃ and in absence of sunlight to form
a) Chlorobenzene
b) Benzyl chloride
c) Benzal chloride
d) Benzene hexachloride
Answer:
a) Chlorobenzene

Question 11.
The name of C₂F₄C₁₂ 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 ehtylidene chloride?
a) Zn / methanol
b) KQH / ethanol
c) aqueous KOH
d) ZnCl₂ / Con HCl
Answer:
c) aqueous KOH

Question 13.
Match the compounds given in Column I with suitable items given in Column II:

Column I (Compound)	Column II (Uses)
A. Iodoform	1. Fire extinguisher
B. Carbon tetra chloride	2. Insecticide
C. CFC	3. Antiseptic
D. DDT	4. Refrigerants

Code
a) A → 2 B → 4 C → 1 D → 3
b) A → 3 B → 2 C → 4 D → 1
c) A → 1 B → 2 C → 3 D → 4
d) A → 3 B → 1 C → 4 D → 2
Answer:
d) A → 3 B → 1 C → 4 D → 2

Question 14.
Assertion:
Inmonohaloarenes, electrophilic substitution occurs at ortho and para positions.
Reason:
Halogen atom is a ring deactivator.
Assertion and Reason type questions.
Directions:
In the following questions, a statement of assertion (A) is followed by a statement of reason (R) mark the correct choice as
(i) If both assertion and reason are true and reason is the correct explanation of assertion.
(ii) If both assertion and reason are true but reason is not the correct explanation of assertion.
(iii) If assertion is true but reason is false.
(iv) If both assertion and reason are false.
a) (i)
b) (ii)
c) (iii)
d) (iv)
Answer:
b) (ii)

Question 15.
Consider the reaction,
CH₃CH₂CH₂Br + NaCN → CH₃CH₂CH₂CN + NaBr This reaction will be the fastest in
a) ethanol
b) methanol
c) DMF (N, N’ – dimethyl formamide)
d) water
Answer:
c) DMF (N, N’ – dimethyl formamide)

Question 16.
Freon – 12 manufactured from tetrachloro methane by
a) Wurtz reaction
b) Swarts reaction
c) Haloform reaction
d) Gattermann reaction
Answer:
b) Swarts reaction

Question 17.
The most easily hydrolysed molecules under S_N¹ condition is
a) allyl chloride
b) ethyl chloride
c) isopropyl chloride
d) benzyl chloride
Answer:
a) allyl chloride

Question 18.
The carbon cation formed in S_N¹ reaction of alkyl halide in the slow step is
a) sp³ hybridized
b) sp² hybridized
c) sp hybridized
d) none of these
Answer:
b) sp² hybridized

Question 19.
The major products obtained when chlorobenzene is nitrated with HNO₃ and con H₂SO₄
a) 1 – chloro – 4 – nitrobenzene
b) 1 – chloro – 2 – nitrobenzene
c) 1 – chloro – 3 – nitrobenzene
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?
a)

b)

c)

d)
Answer:
d)

Question 21.
Ethylidene chloride on treatment with aqueous KOH gives
a) acetaldehyde
b) ethylene glycol
c) formaldehyde
d) glycoxal
Answer:
a) acetaldehyde

Question 22.
The raw material for Raschig process
a) chloro benzene
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) chloropicric acid
Answer:
c) chloropicrin

Question 24.
Acetone X, X is
a) 2 – propanol
b) 2 – methyl – 2 – propanol
c) 1 – propanol
d) acetonol
Answer:
b) 2 – methyl – 2 – propanol

Question 25.
Silverpropionate when refluxed with Bromine in carbon tetrachloride gives
a) propionic acid
b) chloroethane
c) Bromo ethane
d) chloro propane
Answer:
c) bromo ethane

II. Write brief answer to the following questions:

Question 26.
Classify the following compounds in the form of alkyl, allylic, vinyl, benzylic halides.
i) CH₃ – CH = CH – Cl

ii) C₆H₅CH₂I

iii)

iv) CH₂ = CH – Cl
Answer:
i) CH₃ – CH = CH – Cl = Allylic halide

ii) C₆H₅CH₂I = Benzylic halide

iii) = Alkyl halide

iv) CH₂ = CH – Cl = Vinyl halide

Question 27.
Why chlorination of methane is not possible in dark?
Answer:
The reaction of chlorine and methane is a free radical reaction under the influence of light energy. Chlorine molecule first split into two Cl atoms or radicals. These are both very reactive species in contact with methane they form methyl radical and HCl.

Methyl radical further reacts with Cl to give CH₃Cl and another Cl atom thus of a chain reaction. So this reaction takes place only under the influence of light. Hence the reaction does not take place in dark condition.

Question 28.
How will you prepare n propyl iodide from n – propyl bromide?
Answer:
Finkelstein reaction,
nCH₃ – CH₂ – CH₂ – Br + NaI n – CH₃ – CH₂ – CH₂ – I + NaBr
n – propyl iodide                                              n- propyl bromide

Question 29.
Which alkyl halide from the following pair is
i) chiral
ii) undergoes faster S_N² reaction?

Answer:

It contains one chiral carbon atom.
2 – bromo butane undergoes S_N² mechanism faster than 1- Chloro butane.

Question 30.
How does chlorobenzene react with sodium in the presence of ether? What is the name of the reaction?
Answer:
Haloarenes react with sodium metal in dry ether, two aryl groups combine to give biaryl products.
This reaction is called fittig reaction.
C₆H₅Cl + 2Na + Cl – C₆H₅ C₆H₅ – C₆H₅ + 2NaCl
Chlorobenzene                                      Biphenyl

Question 31.
Give reasons for polarity of C – X bond in halo alkane.
Answer:
Carbon halogen bond is a polar bond as halogens are more electro negative than carbon. The carbon atom exhibits a partial positive charge (δ⁺) and halogen atom a partial negative charge (δ^–)

The C -X bond is formed by overlap of sp³ orbital of carbon atom with half-filled p- orbital of the halogen atom. The atomic size of halogen increases from fluorine to iodine, which increases the C – X bond length. Larger the size, greater is the bond length, and weaker is the bond formed. The bond strength of C – X decreases from C – F to C – I in CH₃X.

Question 32.
Why is it necessary to avoid even traces of moisture during the use of Grignard reagent?
Answer:
Grignard reagents are mostly reactive and react with the source of product to give hydrocarbons. Even alcohols, amines, H₂O are sufficiently acidic to convert them to corresponding hydrocarbons.
R Mg X + H₂O → RH +

Due to its high reactivity, it is necessary to avoid even traces of moisture from Grignard reagent.

Question 33.
What happens when acetyl chloride is treated with an excess of CH₃MgI?
Answer:

Question 34.
Arrange the following alkyl halide in increasing order of bond enthalpy of RX.
CH₃Br, CH₃F, CH₃Cl, CH₃I
Answer:
The order is:
CH₃I < CH₃Br < CH₃Cl < CH₃F.

Question 35.
What happens when chloroform reacts with oxygen in the presence of sunlight?
Answer:
2 CHCl₃ + O₂ → 2 COCl₂ + 2 HCl

Question 36.
Write down the possible isomers of C₅H₁₁Br and give their IUPAC and common names.
Answer:
C₅H₁₁Br – Possible isomers
1. CH₃ – CH₂ – CH₂ – CH₂ – CH₂ – Br → 1 – bromo pentane

2. → 2 – bromo pentane

3. → 3 – bromo pentane

4.  → 1 – bromo 2, 2 – dimethyl propane

5. → 1 – bromo 3 – methyl butane

6. → 2 – bromo 3 – methyl butane

7. → 2 – bromo 2 – methyl butane

8. → 1 – bromo 2- methyl butane

9. → (2S) – 1 – bromo 2 – methyl butane

10. → (2R) – 1 – bromo 2 – methyl butane

Question 37.
Mention any three methods of preparation of haloalkanes from alcohols.
Answer:
Haloalkanes are prepared by the following methods.
1) From alcohols:
Alcohols can be converted into halo alkenes by reacting it with any one of the following reagent.
1. Hydrogen halide
2. Phosphorous halides
3. Thionyl chloride.

a) Reaction with hydrogen halide:

Mixture of con. HCl and anhydrous ZnCl₂ is called Lucas Reagent.

The order of reactivity of halo acids with alcohol is in the order HI > HBr > HCl.
The order of reactivity of alcohols with halo acid is tertiary > secondary > primary.

b) Reaction with phosphorous halides:
Alcohols react with PX₅ or PX₃ to form haloalkanes.
Example:
CH₃CH₂OH + PCl₅ → CH₃CH₂Cl + POCl₃ + HCl
Ethane                      Chloro ethane

3CH₃CH₂OH + PCl₃ → 3 CH₃CH₂Cl + H₃PO₃
Ethanol                       Chloro ethane

c) Reaction with Thionyl chloride(Sulphonyl Chloride)
CH₃CH₃OH + SOCl₂ CH₃CH₂Cl + SO₂↑ + HCl↑
Ethanol                                      Chloro ethane

Question 38.
Compare S_N¹ and S_N² reaction mechanisms.
Answer:

	SN1	SN2
Rate law	Unimolecular (Substrate only)	Biomolecular (substrate and nucleophile)
“Big Barrier”	Carbocation stability	Steric hindrance
Alkyl halide (electrophile)	3° > 2° > 1°	1° > 2° > 3°
Nucleophile	Weak (generally neutral)	Strong (generally bearing a negative charge)
Solvent	Polar protic (e.g., alcohols)	Polar aprotic (e.g., DMSO, acetone)
Stereo Chemistry	Mix of retention and inversion	inversion

Question 39.
Reagents and the conditions used in the reactions are given below. Complete the table by writing down the product and the name of the reaction.

Answer:

Question 40.
Discuss the aromatic nucleophilic substitutions reaction of chlorobenzene.
Answer:
The halogen of haloarenes can be substituted by OH^–, NH₂^– or CN^– with appropriate nucleophilic reagents at high temperature and pressure.
Example:
(i) Chlorobenzene reacts with ammonium at 250 and at 50 atm to give aniline.
C₆H₅Cl + 2NH₃ C₆H₅NH₂ + NH₄Cl
Chlorobenzene                  Aniline

(ii) Chlorobenzcne reacts with CuCN in presence of pyridine at 250 to give phenyl cyanide.
C₆H₅Cl + CuCN C₆H₅CN + CuCl
Chlorobenzene                Phenyl cyanide

(iii) Dows process:
C₆H₅Cl + NaOH C₆H₅OH + NaCl
Chlorobenzene                   Phenol
This reaction is known as Dow’s process.

Question 41.
Account for the following:
(i) t – butyl chloride reacts with aqueous KOH by S_N¹ mechanism while n – butyl chloride reacts with S_N² mechanism.
(ii) p – dichloro benzene has higher melting point than those of o – and m – dichloro benzene.
Answer:
(i) t – butyl chloride reacts with aqueous KOH by S_N¹ mechanism while n – butyl chloride reacts with S_N² mechanism.
It general, S_N¹ reaction proceeds through the formation, of carbocation, The tert- butyl chloride readily loses Cl ion to form stable 3° carbocation. Therefore, it reacts with aqueous KOH by S_N¹ mechanism as:

On the other hand n-Butyl chloride does not undergo ionization to form n-Butyl carbocation (1°) because it is not stable. Therefore, it prefers to undergo reaction by S_N² mechanism, which occurs is one step through a transition state involving nucleophilic attack of OH^– ion from the backside with simultaneous expulsion of Cl^– ion from the front side.

S_N¹ mechanism follows the reactivity order as 3° > 2°> 1° while S_N² mechanism follows the reactivity order as 1° > 2° > 3°. Therefore, tert-butyl chloride (3°) reacts by S_N¹ mechanism while n-butyl chloride (1°) reacts by S_N² mechanism. (ii) p – dichloro benzene has higher melting point than those of o – and m – dicholoro benzene. The higher melting point of p – isomer is due to its symmetry which leads to more close packing of its molecules in the crystal lattice and consequently strong intermolecular attractive force which requires more energy for melting. p – Dihalo benzene > o – Dichloro benzene> m – Dichioro benzene
Melting point: 323 K 256 K 249 K

Question 42.
In an experiment methyl iodide in ether is allowed to stand over magnesium pieces. Magnesium dissolves and product is formed.
a) Name of 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) Name of the product and write the equation for the reaction.
CH₃I + Mg CH₃MgI

b) Why all the reagents used in the reaction should be dry? Explain.
All the reagents used in the reaction should be dry because reagent reacts with H20 to produce alkane. This is the reason that everything has to be very dry during the preparation of Grignard reagents.
CH₃ – MgI + H₂O → CH₄ +
Methane

c) How is acetone prepared from the product obtained in the experiment?

Question 43.
Write a chemical reaction useful to prepare the following.
i) Freon – 12 from Carbon tetrachloride
ii) Carbon tetrachloride from carbon disulphide.
Answer:
i) Freon – 12 from Carbon tetrachloride:
Freon – 12 is prepared by the action of hydrogen fluoride on carbon tetrachloride in the presence of catalytic amount of antimony pentachloride.
CCl₄ + 2HF 2HCl + CCl₂F₂
Carbon tetrachloride            Freon – 12

ii) Carbon tetrachloride from carbon disulphide.
Carbon disulphide reacts with chlorine gas in the presence of anhydrous AlCl3 as catalyst giving carbon tetra chloride.
CS₂ + 3 Cl₂ CCl₄ + S₂Cl₂
Carbon disulfide                Carbon tetrachloride

Question 44.
What are Freons? Discuss their uses and environmental effects.
Answer:
The chloro fluoro derivatives of methane and ethane are called freons.
Nomenclature:
Freon is represented as Freon – cba
Where a = number of carbon atoms – 1;
b = number of hydrogen atoms + 1
a = total number of fluorine atoms

Uses:
i) Freons are used as a refrigerants in refrigerators and air conditioners.
ii) It is used as a propellant for aerosols and foams
iii) It is used as propellant for foams to spray out deodorants, shaving creams, and insecticides.

Question 45.
Predict the products when bromo ethane is treated with the following.
i) KNO₂ ii) AgNO₂
Answer:
i) KNO₂:
Bromo ethane reacts with alcoholic solution of NaNO2 or KNO2 to form ethyl nitrite.
CH₃CH₂Br + KNO₂ → CH₃CH₂ – O – N = O + KBr
Bromoethane Ethyl nitrite

ii)AgNO₂:
Bromo ethane reacts with alcoholic solution of AgNO2 to form nitro ethane.
CH₃CH₂Br + AgNO₂ → CH₃CH₂ NO₂ + AgBr
Bromoethane                Nitro ethane

Question 46.
Explain the mechanism of S_N¹ reaction by highlighting the stereochemistry behind it.
Answer:

In S_N¹ reactions, if the alkyl halide is optically active, the product obtained in a racemic mixture. The intermolecular carbocation formed in slowest step being sp2 hybridised is planar species. Therefore the attack of the nucleophile OH on it, can occur from both the faces with equal case forming a mixture of two enantiomers. Thus S_N¹ reaction of optically active alkyl halides are accompained by racemisation.

Question 47.
Write short notes on the following.
i) Raschig process
ii) Dows process
iii) Darzen’s process
Answer:
i) Raschig process:
Chloro benzene is commercially prepared by passing a mixture of benzene vapour, air and HCl overheated cupric chloride, this reaction is called the Raschig process,

ii) Dows Process:
C₆H₅Cl + NaOH C₆H₅OH + NaCl
This reaction is known as Dows process.

iii) Darzen’s process:
CH₃CH₂OH + SOCl CH₃CH₂Cl + SO₂↑ + HCl↑
Ethanol Chloro ethane
This reaction is known as Darzen’s process.

Question 48.
Starting from CH₃MgI, How will you prepare the following?
i) Acetic acid
ii) Acetone
iii) Ethyl acetate
iv) Iso propyl alcohol
v) Methyl cyanide
Answer:
i) Acetic acid:
Solid carbon dioxide reacts with methyl magnesium iodide to form addition product which on hydrolysis yields aceti acid.

ii) Acetone:
Acetyl chloride reacts with methyl magnesium iodide and followed by acid hydrolysis to give acetone.

iii) Ethyl Acetate:
Ethyl chloroformate reacts with methyl magnesium iodide to form ethyl acetate.

iv) Isopropyl alcohol:
Aldehydes (Acetaldehyde) other than formaldehyde, react with methyl magnesium iodide to give addition product which on hydrolysis yields isopropyl alcohol.

v) Methyl cyanide:
Methyl magnesium iodide reacts with cyanogen chloride to give methyl cyanide.

Question 49.
Complete the following reactions.
i) CH₃ – CH = CH₂ + HBr
ii) CH₃ – CH₂ – Br + NaSH
iii) C₆H₅Cl + Mg
iv) CHCl₃ + HNO₃
v) CCl₄ + H₂O
Answer :
i) CH₃ – CH = CH₂ + HBr CH₃ – CH₂ – CH₂ – Br
Propene                                                   n – propyl bromide

ii) CH₃ – CH₂ – Br + NaSH CH₃ – CH₂ – SH + NaBr
Propyl bromide                                     Ethanethiol

iii) C₆H₅Cl (Chloro benzene) + Mg C₆H₅MgCl (Phenyl magnesium chloride)

iv) CHCl₃ + HNO₃ CCl₃NO₂ + H
Chloroform                               Chloropicrin

v) CCl₄ (Carbon tetrachloride) + H₂O COCl₂ (Carbonyl chloride) + 2HCl

Question 50.
Explain the preparation of the following compounds.
i) DDT
ii) Chloroform
iii) Biphrnyl
iv) Chloropicrin
v) Freon – 12
Answer:
i) DDT:
DDT can be prepared by heating a mixture of chlorobenzene with chloral (Trichloro acetaldehyde) in the presence of con.H₂SO₄.

ii) Chloroform:
Preparation:
Chloroform is prepared in the laboratory by the reaction between ethyl alcohol with bleaching powder followed by the distillation of the product chloroform. Bleaching powder act as a source of chlorine and calcium hydroxide. This reaction is called haloform reaction. The reaction proceeds in three steps as shown below.

Step – 1: Oxidation
CH₃CH₂OH + Cl₂ → CH₃CHO + 2HCl
Ethyl alcohol           Ethanal (Acetaldehyde)

Step – 2: Chlorination
CH₃CHO + 3Cl₂ → CCl₃CHO + 3HCl
Acetaldehyde        Trichloro acetaldehyde

Step – 3: Hydrolysis
2CCl₃CHO + Ca(OH)₂ → 2CHCl₃ + (HCOO)₂ Ca
Chloral                         chloroform

iii) Biphenyl:
Chloro benzene react with sodium metal in dry ether, to give biphenyl. This reaction is called fitting reaction.
C₆H₅Cl + 2 Na + Cl – C₆H₅ C₆H₅ – C₆H₅ + 2NaCl
Chloro benzene                                          Biphenyl

iv) Chloropicrin:
Chloroform reacts with nitric acid to form chloropicrin. (Trichloro nitro methane)
CHCl₃ + HNO₃ CCl₃NO₂ + H₂O
Chloroform                   Chloropicrin

v) Freon – 12
Freon – 12 is prepared by the action of hydrogen fluoride on carbon tetrachloride in the presence of catalytic amount of antimony pentachloride
CCl₄ + 2 HF 2 HCl + CCl₂F₂
Carbon tetrachloride                     Freon – 12

Question 51.
An organic compound (A) with molecular formula C₂H₅Cl reacts with KOH gives compounds (B) and with alcoholic KOH gives compound (C). Identify (A), (B), (C).
Answer:

Question 52.
Simplest alkene (A) reacts with HCl to form compound (B). Compound (B) reacts with ammonia to form compound (C) of molecular formula C₂H₇N. Compound (C) undergoes carbylamine test. Identify (A),
(B) and (C).
Answer:
CH₂ = CH₂ + HCl → C₂H₅Cl
(A) Ethylene              (B) Ethyl chloride

C₂H₅Cl + NH₃    →    C₂H₅NH₂ + HCl
(C) Ethyl chloride      (B) Ethyl amine

Question 53.
A hydrocarbon C₃H₆(A) reacts with HBr to form compound (B). Compound (B) reacts with aqueous potassium hydroxide to give (C) of molecular formula C₃H₆O. What are the (A), (B) and (C). Explain the reactions.
Answer:

Question 54.
Two isomers (A) and (B) have the same molecular formula C₂H₄Cl₂. Compound (A) reacts with aqueous KOH gives compound (C) of molecular formula C₂H₄O. Compound (B) reacts with aqueous KOH gives compound (D) of molecular formula C₂H₆O₂. Identify (A), (B), (C) and (D).
Answer:

11th Chemistry Guide Haloalkanes and Haloarenes Additional Questions and Answers

I. Choose the best answer:

Question 1.
Which of the following is 1° alkyl halide
a) R – CH₂ – X
b) R₂CHX
C) R₃C – X
d) R – H
Answer:
a) R – CH₂ – X

Question 2.
2° halide among the following
a) isopropyl chloride
b) iso – butyl chloride
c) n – propyl chloride
d) n – butyl chloride
Answer:
a) isopropyl chloride

Question 3.
Ethylidene dibromide is
a) CH₃CH₂Br
b) Br – CH₂ – CH₂ – Br
c) CH₃ – CHBr₂
d) CH₂ = CH Br
Answer:
c) CH₃ – CHBr₂

Question 4.
Which of the following is gemdihalide?
a) CH₃CHBrCH₂Br
b) CH₃CHBr₂
c) CH₃CHBrCH₂CH₂Br
d) BrCH₂CH₂Br
Answer:
b) CH₃CHBr₂

Question 5.
Vicinal dihalide is
a) CH₃CH₂Br
b) Br – CH₂ – CH₂ – Br
c) CH₃ – CHBr₂
d) CH₂ = CHBr
Answer:
b) Br – CH₂ – CH₂ – Br

Question 6.
The reagent used to get alkyl halide from alcohol
a) PCl₅
b) SOCl₂
c) Both a and b
d) Cl₂
Answer:
c) Both a and b

Question 7.
For the preparation of alkyl halides from alcohols which among the following cannot be used
a) PCl₅
b) SOCl₂
c) PCl₃
d) NaCl
Answer:
d) NaCl

Question 8.
In the preparation of alkyl halide from alkane and halogen which of the following reaction involved
a) Electrophilic addition
b) Nucleophilic addition
c) Electrophilic substitution
d) Nucleophilic substitution
Answer:
a) Electrophilic addition

Question 9.
In the preparation of alkyl halide from alkane and halogen which of the following reaction involved
a) Free radical substitution
b) Nucleophilic addition
c) Electrophilic substitution
d) Nucleophilic substitution
Answer:
a) Free radical substitution

Question 10.
Grignard reagent is formed when alkyl halide reacts with which one of the following
a) Mg in alcohol
b) Mg in acid
c) Mg in dry ether
d) MgO
Answer:
c) Mg in dry ether

Question 11.
When alkyl halide reacts with moist Ag₂O gives
a) alcohol
b) ether
c) alkane
d) Alkene
Answer:
a) alcohol

Question 12.
Alkyl halide on reduction with Zn + HCl gives
a) alcohol
b) alkene
c) alkane
d) ether
Answer:
c) alkane

Question 13.
Cyanide is formed as the major product of the reaction when alkyl halide is treated with one of the following :
a) AgNO₂
b) KNO₂
c) AgCN
d) KCN
Answer:
c) AgCN

Question 14.
Which of the reactions are most common in alkyl halides
a) Nucleophilic addition
b) Electrophilic addition
c) Nucleophilic substitution
d) Electrophilic substitution
Answer:
c) Nucleophilic substitution

Question 15.
Treatment of ammonia with excess of ethyl chloride will yield
a) Diethyl amine
b) Ethane
c) Tetra ethyl ammonium chloride
d) methyl amine
Answer:
c) Tetra ethyl ammonium chloride

Question 16.
In chloro ethane the carbon bearing halogen is bonded to ________.
a) three, primary
b) two, secondary
c) one, tertiary
d) two, primary
Answer:
d) two, primary

Question 17.
Which of the fallowing is used as refrigerant?
a) CH₃COCH₃
b) CCl₄
c) C₂H₅Cl
d) CF₄
Answer:
c) C₂H₅Cl

Question 18.
SN¹reaction occurs through the intermediate formation of
a) carbocation
b) carbanion
c) free radicals
d) transition
Answer:
a) carbocation

Question 19.
The rate of SN² reaction is maximum when the solvent is
a) Methyl alcohol
b) Water
c) Dimethyl sulphoxide
d) Benzene
Answer:
c) Dimethyl sulphoxide

Question 20.
The most reactive nucleophile among the following is
a) CH₃O^–
b) C₆H₅O^–
c) (CH₃)₂CHO^–
d) (CH₃)₃CO^–
Answer:
a) CH₃O^–

Question 21.
The correct order of reactivity towards nucleophilic substitution reaction is
a) CH₃F > CH₃Cl > CH₃Br > CH₃I
b) CH₃I > CH₃Br > CH₃Cl > CH₃F
C) CH₃I > CH₃Cl > CH₃Br > CH₃F
d) CH₃I > CH₃Br > CH₃F > CH₃Cl
Answer:
b) CH₃I > CH₃Br > CH₃Cl > CH₃F

Question 22.
In SN₂ reactions the order of reactivity of the halides.
CH₃X, C₂H₅X , n – C₃H₇X, n- C₄H₉X is
a) CH₃X > C₂H₅X > n – C₃H₇X > n – C₄H₉X
b) C₂H₅X > n – C₃H₇X > n – C₄H₉X > CH₃X
c) C₂H₅X > n – C₃H₇X > n – C₄H₉X < CH₃X
d) n – C₄H₉X > n – C₃H₇X > C₂H₅X > CH₃X
Answer:
a) CH₃X > C₂H₅X > n – C₃H₇X > n – C₄H₉X

Question 23.
SN² mechanism proceeds through the formation of a
a) carbocation
b) transition state
c) free radical
d) carbanion
Answer:
b) transition state

Question 24.
In Dow’s process the starting raw material is
a) Phenol
b) Chloro benzene
c) Aniline
d) Diazobenzene
Answer:
b) Chloro benzene

Question 25.
Chloro benzene is prepared commercially by
a) Dow’s process
b) Decon’s process
c) Raschig process
d) Etard’s process
Answer:
c) Raschig process

Question 26.
Chloro benzene is ________ reactive than benzene towards electrophilic substitution and directs incoming electrophile to the ______ position.
a) more, ortho & para
b) less, ortho & para
c) more, meta
d) less, meta
Answer:
b) less, ortho & para

Question 27.
The raw material for raschig; process is
a) chloro benzene
b) phenol
c) benzene
d) anisol
Answer:
c) benzene

Question 28.
Chloro benzene on treatment with sodium in dry ether gives diphenyl. The name of the reaction is
a) Fitting reaction
b) Wurtz fittig reaction
c) Wurtz reaction
d) Sandmeyer reaction
Answer:
a) Fitting reaction

Question 29.
An organic compound which produces a bluish green coloured flame on heating in the presence of copper is,
a) chloro benzene
b) benzaldehyde
c) aniline
d) benzoic acid
Answer:
a) chloro benzene

Question 30.
The raw materials for the commercial manufacture of DDT are
a) chloro benzene and chloroform
b) chloro benzene and chloro methane
c) chloro benzene and chloral
d) chloro benzene and iodoform
Answer:
c) chloro benzene and chloral

Question 31.
Iodoform is used as
a) anaesthetic
b) antiseptic
c) analgesic
d) anti febrin
Answer:
b) antiseptic

Question 32.
The following is used in paint removing
a) CHCl₃
b) CH₂Cl₂
c) CCl₄
d) CH₃CI
Answer:
b) CH₂Cl₂

Question 33.
In fire extinguishers, following is used
a) CHCl₃
b) CS₂
c) CCl₄
d) CH₂Cl₂
Answer:
c) CCl₄

Question 34.
The following is used for metal cleaning and finishing
a) CHCl₃
b) CHI₃
c) CH₂Cl₂
d) C₆H₆
Answer:
c) CH₂Cl₂

Question 35.
First chlorinated insecticide
a) DDT
b) Gammaxene
c) Iodoform
d) Freon
Answer:
a) DDT

Question 36.
The following is used as anaesthetic
a) C₂H₄
b) CHCl₃
c) CH₂Cl₂
d) DDT
Answer:
b) CHCl₃

Question 37.
Freon – 12 is
a) CF₃Cl
b) CHCl₂F
c) CF₂Cl₂
d) DDT
Answer:
c) CF₂Cl₂

Question 38.
The name of DDT
a) p, p’ – dichloro diphenyl trichloro ethane
b) p, p’ – dichloro diphenyl trichloro ethene
C) p, p’ – dichloro diphenyl tnchloro benzene
d) p, p’ – tetra chloro ethane
Answer:
a) p, p’ – dichloro diphenyl trichloro ethane

Question 39.
Freon R – 22 is
a) CHClF₂
b) CCl₂F₂
c) CH₃Cl
d) CH₂Cl₂
Answer:
a) CHClF₂

Question 40.
Molecular formula of DDT has
a) 5 Cl atoms
b) 4 Cl atoms
c) 3 Cl atoms
d) 2 Cl atoms
Answer:
a) 5 Cl atoms

Question 41.
What is DDT among the following
a) Green house gas
b) A fertilizer
c) Bio degradable pollutant
d) Non – Bio degradable pollutant
Answer:
d) Non – Bio degradable pollutant

Question 42.
The IUPAC name of (CH₃)₃CHCH₂Br is
a) 1 – bromo – 2 – methyl propane
b) 2 – bromo – 2 -methyl propane
c) 1 – bromo – 1 – methyl propane
d) 2 – bromo – 1 -methylpropane
Answer:
a) 1 – bromo – 2 – methyl propane

Question 43.
IUPAC name of allyl chloride is
a) 1 – chloro ethane
b) 3 – chloro- 1 – propyne
c) 3 – chloro – 1 – propene
d) 1 – chloro propane
Answer:
c) 3 – chloro – 1 – propene

Question 44.
The number of structural isomers possible with the formula C₄H₉Cl are
a) 5
b) 4
c) 3
d) 2
Answer:
b) 4

Question 45.
Density is highest for
a) CH₃Cl
b) CH₂Cl₂
c) CHCl₃
d) CCl₄
Answer:
d) CCl₄

Question 46.
C₂H₅OH X. In this reaction ‘X’ is
a) Ethanol
b) Ethylene chloride
c) ethylidene chloride
d) ethyl chloride
Answer:
d) ethyl chloride

Question 47.
Thionyl chloride is preferred in the preparation of chloro compound from alcohol since
a) Both the byproducts are gases and they escape out leaving product in pure state
b) It is a chlorinating agent
c) It is an oxidising agent
d) All other reagents are unstable
Answer:
a) Both the byproducts are gases and they escape out leaving product in pure state

Question 48.
The only alkene which gives primary alkyl halides on hydro halogenation
a) C₂H₄
b) C₃H₆
c) C₄H₈
d) C₅H₁₀
Answer:
a) C₂H₄

Question 49.
– OH cannot be replaced by – Cl if we use
a) PCl₅
b) PCl₃
c) S₂Cl₂
d) SOCl₂
Answer:
c) S₂Cl₂

Question 50.
In the hydrohalogenation of ethylene for adding HCl, the catalyst used is
a) Anhydrous AlCl₃
b) Conc. Sulphuric acid
c) Dilute Sulphuric acid
d) Anhydrous ZnCl₂
Answer:
a) Anhydrous AlCl₃

Question 51.
Which one of the following has the lowest boiling point?
a) CH₃Cl
b) C₂H₅Cl
c) C₂H₅Br
d) C₂H₅I
Answer:
a) CH₃Cl

Question 52.
Chloroethane is reacted with alcoholic potassium hydroxide. The product formed is
a) C₂H₆O
b) C₂H₆
c) C₂H₄
d) C₂H₄O
Answer:
c) C₂H₄

Question 53.
What is X in the following reaction? C₂H₅Cl + X → C₂H₅OH + KCl
a) KHCO3
b) alc. KOH
c) aq. KOH
d) K₂CO₃
Answer:
c) aq. KOH

Question 54.
Which of the following acids will give maximum yield of alkyl chloride in Hunsdiecker reaction
a) CH₃CH₂CH₂COOH
b) (CH₃)₂CHCOOH
c) (CH₃)₃CCOOH
d) C₆H₅CH (CH₃)COOH
Answer:
a) CH₃CH₂CH₂COOH

Question 55.
In the reaction sequence
C₂H₅Cl + KCN X. What is the molecular formula of X is
a) C₂H₅CN
b) C₂H₅NC
c) C₂H₅OH
d) C₂H₄O
Answer:
a) C₂H₅CN

Question 56.
Ethyl chloride on heating with silver cyanide forms a compound X. The functional isomer of X is
a) C₂H₅NC
b) C₂H₅NCN
c) H₃C – NH – CH₃
d) C₂H₅NH₂
Answer:
b) C₂H₅NCN

Question 57.
With Zn – Cu couple and C₂H₅OH, ethyl Iodide reacts to give
a) ethers
b) diethyl ether
c) Iodoform
d) Ethane
Answer:
d) Ethane

Question 58.
Ethyl bromide on boiling with alcoholic solutions of sodium hydroxide forms
a) Ethane
b) ethylene
c) ethyl alcohol
d) all of these
Answer:
b) ethylene

Question 59.
Following major compound is formed when ethyl chloride react with silver nitrite
a) Nitro ethane
b) Ethyl nitrite
c) Ethylene
d) Acetaldehyde
Answer:
b) Ethyl nitrite

Question 60.
Which of the following represents Williamson’s synthesis?
a) CH₃COOH + PCl₃ →
b) CH₃ – CH₂ – Cl + CH₃COOH →
c) CH₃ – CH₂ – ONa + CH₃ – CH₂ – Cl →
d) CH₃ – CH₂ – OH + Na →
Answer:
c) CH₃ – CH₂ – ONa + CH₃ – CH₂ – Cl →

Question 61.
The reaction of alkyl halide with benzene in presence of anhydrous A1Cl₃ gives alkyl benzene the reaction is known as
a) Friedel – craft’s reaction
b) Carbylamine reaction
c) Gattermann reaction
d) Wurtz reaction
Answer:
a) Friedel – craft’s reaction

Question 62.
A Grignard’s reagent reacts with water to give
a) ether
b) alkanes
c) amine
d) Alcohol
Answer:
b) alkanes

Question 63.
C₂H₅Cl + Mg → C₂H₅ MgCl in this reaction the solvent is
a) C₂H₅OH
b) Water
c) Dry ether
d) Acetone
Answer:
c) Dry ether

Question 64.
For a nucleophilic substitution reaction the rate was found in the order RI > RBr > RCl > RF then the reaction could be
a) S_N¹ only
b) S_N² only
c) Either S_N¹ or S_N²
d) Neither S_N¹ or S_N²
Answer:
c) Either S_N¹ or S_N²

Question 65.
S_N² reaction leads to
a) inversion of configuration
b) retention of configuration
c) partial racemisation
d) no racemisation
Answer:
a) inversion of configuration

Question 66.
Which of the following alkyl halide is hydrolysed by S_N¹ mechanism
a) CH₃Cl
b) CH₃ – CH₂ – Cl
c) CH₃ – CH₂ – CH₂ – Cl
d) (CH₃)₃CCl
Answer:
d) (CH₃)₃CCl

Question 67.
S_N¹ reaction is favoured by
a) non – polar solvents
b) Bulky group on the carbon atom attached to the halogen atom
c) Small groups on the carbon atom attached to halogen atom
d) All of the above
Answer:
b) Bulky group on the carbon atom attached to the halogen atom

Question 68.
Which of the following is not stereospecific
a) S_N¹
b) S_N²
c) E₂
d) Addition of Br₂ to ethylene in CCl₄
Answer:
a) S_N¹

Question 69.
Which of the following factors does not favour S_N¹ mechanism
a) Strong base
b) Polar solvent
c) Low. conc. of nucleophile
d) 3° halide
Answer:
c) Low. conc. of nucleophile

Question 70.
The order of reactivity of various alkyl halides toward SN1 reaction is
a) 3° > 2° > 1°
b) 1° > 2° > 3°
c) 3° = 2° = 1°
d) 1° > 3° > 2°
Answer:
a) 3° > 2° > 1°

Question 71.
In aryl halides carbon atom holding halogen is
a) sp² hybridised
b) sp hybridised
c) sp³ hybndised
d) sp³d hybridised
Answer:
a) sp² hybridised

Question 72.
Chloro benzene can be prepared by reacting benzene diazonlum chloride with
a) HCl
b) Cu₂Cl₂ / HCl
c) Cl₂ / AlCl₃
d) HNO₂
Answer:
b) Cu₂Cl₂ / HCl

Question 73.
+ Cl₂ X, X is
a) Chloro benzene
b) m – dichloro benzene
c) benzene hexachioride
d) p – dichlorobenzene
Answer:
a) Chloro benzene

Question 74.
The following is an example of Sandmeyer reaction
a) C₆H₅N₂⁺ Cl^– C₆H₅Cl
b) C₆H₅N₂⁺ Cl^– C₆H₅OH
c) C₆H₅N₂⁺ Cl^– C₆H₅F
d) C₆H₅N₂⁺ Cl^– C₆H₅Cl
Answer:
a) C₆H₅N₂⁺ Cl^– C₆H₅Cl

Question 75.
Chlorobenzene on reaction with CH₃Cl in presence of AlCl₃ gives
a) toulene
b) m – chloro toulene
c) only o – chloro toulene
d) mixture of o – and p – chlorotoulene
Answer:
d) mixture of o – and p – chlorotoulene

Question 76.
2C₆H₅Cl + 2Na → X, X is
a) toulene
b) biphenyl
C) phenyl ethane
d) 1 – chloro – 2 – phenyl ethane
Answer:
b) biphenyl

Question 77.
Chlorobenzene on fusing with solid NaOH gives
a) benzene
b) benzoic acid
c) phenol
d) benzene chloride
Answer:
c) phenol

Question 78.
Chlorobenzene on nitration gives major product of
a) 1 – chloro – 4 – nitro benzene
b) 1 – chloro – 3 – nitro benzene
c) 1, 4 – dinitro benzene
d) 2, 4, 6 – tri nitro benzene
Answer:
a) 1 – chloro – 4 – nitro benzene

Question 79.
The reaction C₆H₅I + 2 Na + CH₃I → C₆H₅CH₃ + 2 NaI is
a) Wurtz reaction
b) Fittig reaction
c) Wurtz-Fittig reaction
d) Sandmeyer reaction
Answer:
c) Wurtz-Fittig reaction

Question 80.
R – Cl + Nal R – I + NaCl. This reaction is
a) Wurtz reaction
b) Fittig reaction
c) Finkelstein reaction
d) Frankland reaction
Answer:
c) Finkelstein reaction

Question 81.
C₂H₅OH + SOCl₂ x + y + z. In this reaction x, y and z respectively are
a) C₂H₄Cl₂, SO₂, HCl
b) C₂H₅Cl, SO₂, HCl
c) C₂H₅Cl, SOCl, HCl
d) C₂H₄, SO₂, Cl₂
Answer:
b) C₂H₅Cl, SO₂, HCl’

Question 82.
C₂H₅Cl + AgOH → A + AgCl.
A + CH₃COCl → C + HCl. “C” is
a) Ethyl acetate
b) Methyl acetate
c) butanone – 2
d) propanone
Answer:
a) Ethyl acetate

Question 83.
The compound (B) in the below reaction is:
C₂H₅Cl A B
a) ethylene chloride
b) acetic acid
c) propionic acid
d) ethyl cyanide
Answer:
c) propionic acid

Question 84.
Chloro ethane reacts with X to form diethyl ether. What is X?
a) NaOH
b) H₂SO₄
c) C₂H₅ONa
d) Na₂S₂O₃
Answer:
c) C₂H₅ONa

Question 85.
1 – chlorobutane on reaction with alcoholic potash gives
a) 1 – butene
b) 1 – butanol
c) 1 – butyne
d) 2 – butanol
Answer:
a) 1 – butene

Question 86.
Propane nitrile may be prepared by heating
a) Propyl alcohol with KCN
b) ethyl chloride with KCN
c) Propyl chloride with KCN
d) ethyl chloride with KCN
Answer:
d) ethyl chloride with KCN

Question 87.
CH₃CH = CH₂ A B, B is
a) propanol – 2
b) propanal – 1
c) propanol – 1
d) propanal – 2
Answer:
c) propanol – 1

Question 88.
Y is

Answer:
c)

Question 89.
The correct order of increasing boiling points is
a) 1 – chloropropane < isopropylchloride < 1 – chlorobutane
b) isopropylchloride < 1 – chloropropane < 1 – chlorobutane
c) 1 – chlorobutane < isopropylchloride < 1 – chloropropane
d) 1 – chlorobutane < 1 – chloropropane < isopropylchloride
Answer:
b) isopropylchloride < 1 – chloropropane < 1 – chlorobutane

Question 90.
The correct order of decreasing S_N² reactivity
a) RCH₂X > R₂CHX > R₃CX
b) RCH₂X > R₃CX > R₂CHX
c) R₂CHX > R₃CX > RCH₂X
d) R₃CX > R₂CHX > RCH₂X
Answer:
a) RCH₂X > R₂CHX > R₃CX

II. Very short question and answer (2 Marks):

Question 1.
What are haloalkanes? Give example.
Answer:
Mono halogen derivatives of alkanes are called haloalkanes. Haloalkanes are represented by general formula R – X, Where, R is an alkyl group (C_nH_{2n + 1}) – and X is a halogen atom (X = F, Cl, Br or I). Haloalkanes are further classified into primary, secondary, tertiary haloalkane on the basis of type of carbon atom to which the halogen is attached.
Example:

Question 2.
How will you convert methane into tetra chloro methane?
Answer:
Chlorination of methane gives different products which have differences in the boiling points. Hence, these can be separated by fractional distillation.

Question 3.
What is Finkelstein reaction?
Answer:
Chloro or bromoalkane on heating with a concentrated solution of sodium iodide in dry acetone gives iodo alkanes. This reaction is called as Finkelstein reaction.
CH₃CH₂Br + NaI CH₃CH₂I + NaI
Bromo ethane Iodoethane

Question 4.
What is Swartz reaction?
Answer:
Chloro or bromo alkanes on heating with metallic fluorides like AgF or SbF₃ gives fluoro alkanes. This reaction is called Swarts reaction.
CH₃CH₂Br + AgF CH₃CH₂F + AgBr
Bromo ethane Fluoro ethane

Question 5.
What is Hunsdiecker reaction?
Answer:
Silver salts of fatty acids when refluxed with bromine in CCl₄ gives bromo alkane.
CH₃CH₂COOAg + Br₂ CH₃CH₂Br + CO₂ + AgBr
Silver propionate Bromo ethane

Question 6.
How is ehtyl magnesium bromide prepared from ethyl bromide?
Answer:
When a solution of ethyl bromide in ether is treated with magnesium, we get ethyl magnesium bromide.
CH₃ – CH₂ – Br + Mg CH₃CH₂MgBr
Ethyl bromide Ethyl magnesium bromide

Question 7.
How will you convert ethyl bromide into ethyl lithium?
Answer:
Ethyl bromide reacts with active metals like sodium, lead etc in the presence of dry ether to form ethyl lithium.
CH₃ CH₂ Br + 2Li CH₃ CH₂Li + LiBr
Ethyl bromide Ethyl Lithium

Question 8.
How is TEL prepared from ethyl bromide?
Answer:
When ethyl bromide reacts with Na / Pb alloy to give TEL.
4CH₃ CH₂ Br + 4Na/Pb → (CH₃CH₂)₄Pb + 4NaBr + 3Pb
Ethyl bromide Sodium-lead alloy Tetra ethyl lead (TEL)

Question 9.
What are organic metallic compounds? Give example.
Answer:
Organo metallic compounds are organic compounds in which there is a direct carbon-metal bond
Example:
CH₃ Mg I – Methyl magnesium iodide
CH₃CH₂Mg Br – Ethyl magnesium bromide

Question 10.
How is methane prepared from Grignard reagent?
Answer:
Compounds like water, alcohols and amines which contain active hydrogen atom react with Grignard reagents to form alkanes.
CH₃MgI + HO – H → CH₄ + Mg I (OH)

CH₃MgI + C₂H₅OH          CH₄ + MgI (OC₂H₅)
Ethyl alcohol                Methane

Question 11.
What are Haloarenes? Give a suitable example.
Answer:
Haloarenes are the compounds in which the halogen is directly attached to the benzene ring.
Example:

Question 12.
How is chloro benzene prepared from benzene by direct halogenation?
Answer:
Chloro benzene is prepared by the direct chlorination of benzene in the presence of lewis acid catalyst like FeCl₃.

Question 13.
Write a note on Sand Meyer reaction.
Answer:
When aqueous solution of benzene diazonium chloride is warmed with Cu₂Cl in HCl gives chioro benzene.

Question 14.
How is Iodo benzene prepared from benzene diazonium chloride?
Answer:
Iodo benzene is prepared by warming benzene diazonium chloride with an aqueous KI solution.
C₆H₅N₂Cl + Kl          C₆H₅I + N₂ + KCl
Benzene dizonium chloride        Iodo benzene

Question 15.
What happens when ethylidene dichloride is treated with Zinc dust in methanol?
Answer:
Gem dihalides and vic – dihalides on treatment with zinc dust in methanol give alkenes.
CH₃ – CHCl₂ + Zn CH₂ = CH₂ + ZnCl₂
Ethylidene dichloride                     Ethylene

Question 16.
How will you convert chloroform into methylene chloride?
Answer:
a) Reduction of chloroform in the presence of Zn + HCl gives methylene chloride.
CHCl₃ (chloroform) CH₂Cl (Methylene chloride) + HCl
b) Reduction of chloroform using H2/Ni
CHCl₃ (chloroform) CH₂Cl₂ (Methylene chloride) + HCl

Question 17.
Write the chlorination reaction of methane.
Answer:
Chlorination of methane gives methylene chloride
CH₄ CH₃Cl CH₂Cl₂
Methane                                               Methylene chloride

Question 18.
How is chloroform prepared from carbon tetrachloride?
Answer:
Carbon tetrachloride is reduced by iron powder in dilute HCl medium to form chloroform
CCl₄ (carbon tetrachloride) + 2[H] CHCl₃ (chloroform) + HCl

III. Short question and answers (3 Marks):

Question 1.
write IUPAC name of the following.
i)

ii)

iii)
Answer:
i)

ii)

iii)

Question 2.
Write the structure of the following compounds.
i) 1 – Bromo – 4 – ethyl cyclohexane
ii) 1, 4 – Dichlorobut – 2 – ene
iii) 2 – chloro – 3 – methyl pentane
Answer:
i) 1 -Bromo – 4 – ethyl cyclohexane:

ii) 1, 4 – Dichlorobut – 2 – ene
– Cl – CH₂ – CH = CH – CH₂ – Cl

iii) 2 – chloro – 3 – methyl pentane

Question 3.
Write any three methods of preparation of chloro ethane from ethanol.
Answer:
a) Reaction with hydrogen halide:
Ethanol is heated with HCl in presence of anhydrous ZnCl₂ to give ethyl chloride.
CH₃CH₂OH + HCl CH₃CH₂Cl + H₂O
Ethanol Chloroethane

b) Reaction with phosphorous halides:
Ethanol reacts with PCl₅ or PCl₃ it gives ethyl chloride.
CH₃CH₂OH + PCl₅ → CH₃CH₂Cl + POCl₃ + HCl
Ethanol                      Chloro ethane

3 CH₃CH₂OH + PCl₃ → 3CH₃CH₂Cl + H ₃PO₃
Ethanol                        Chloro ethane

C) Reaction with thionyl chloride (Sulphonyl chloride):
When ethanol reacts with SOCl₂ in presence of pyridine, it gives chloro ethane.
CH₃CH₂OH + SOCl₂ CH₃CH₂Cl + SO₂ + HCl
Ethanol                                            Chloro ethane

Question 4.
What happens when haloalkane reacts with aqueous alkali or most silver oxide?
Answer:
Ethyl bromide reacts with aqueous solution of KOH or moist silver oxide (Ag₂O/H₂O) to form ethanol.
CH₃ – CH₂ – Br + KOH (aq) CH₃CH₂ – OH + KBr
Bromoethane                                   Ethyl alcohol

CH₃ – CH₂ – Br   +   AgOH(aq)    CH₃CH₂ – OH + AgBr
Bromoethane         Moist silver oxide            Ethanol

Question 5.
Explain the ammonolysis reaction of bromo ethane.
Answer:
Ethyl bromide reacts with alcoholic ammonia solution to form ethylamine.
CH₃ – CH₂ – Br + H – NH₂ → CH₃ CH₂ – NH₂ + HBr
Bromo ethane                        Ethyl amine

However, with excess of ethyl bromide, secondary and tertiary amines along with quaternary ammonium salts are obtained.

Question 6.
What happens when bromoethane reacts with alcoholic KCN and alcoholic AgCN?
Answer:
Reaction with alcoholic KCN:
Ethyl bromide reacts with alcoholic KCN solution to form ethyl cyanides.
CH₃ – CH₂ – Br + KCN → CH₃ – CH₂ – CN + KBr
Bromoethane                    Ethyl cyanide

Reaction with alcoholic AgCN:
Haloalkanes react with alcoholic AgCN solution to form alkyl isocyanide.
CH₃CH₂Br + AgCN → CH₃CH₂NC + AgBr
Bromoethane           Ethyl isocyanide

Question 7.
How are the following compounds prepared from bromo ethane?
i) Ethane thiol
(ii) Diethyl ether
Answer:
i) Ethane thiol:
Ethyl bromide reacts with sodium or potassium hydrogen sulphide to form thio alcohols.
CH₃CH₂Br CH₃CH₂SH + NaBr
Bromo ethane                           Ethane thiol

ii) Diethyl ether:
Ethyl bromide, when boiled with sodium alkoxide gives diethyl ether. This method can be used to prepare mixed (unsymmetrical) ethers also.
CH₃ – CH₂Br +      NaOCH₂CH₃          CH₃CH₂ – O – CH₂CH₃ + NaBr
Bromo ethane        Sodium ethoxide                 diethyl ether

Question 8.
How is ethane prepared from the following compounds?
i) Bromo ethane ii) Iodo ethane
Answer:
i) From bromo ethane:
Ethyl bromide is reduced to ethane by treating with H₂ in the presence of metal catalyst like nickel, palladium etc or with hydroiodic acid in the presence of red phosphrous.
Ni(or)Pd
CH₃CH₂Br + H₂ CH₃ – CH₃ + HBr
Bromo ethane                              Ethane

ii) From iodo ethane:
Iodo ethane is reduced with H₂ in presence of Red P it gives ethane.
CH₃CH₂I + HI CH₃ – CH₃ + I₂
Iodo ethane                         Ethane

Question 9.
Write the uses of carbon tetra chloride.
Answer:

1. Carbon tetrachloride is used as dry cleaning agent.
2. It is used as a solvent for oils, fats and waxes
3. As the vapour of CCl₄ is non-combustible, it is used under the name pyrene for extinguishing the fire in oil or petrol.

Question 10.
Write the uses of Grignard reagents.
Answer:

1. Grignard reagents are synthetically very useful compounds. These reagents are converted to various organic compounds like alcohols, carboxylic acids, aldehydes and ketones.
2. The alkyl group being electron rich acts as a carbanion or a nucleophile.
3. They would attack polarized molecules at a point of low electron density. The following reactions illustrate the synthetic uses of Grignard reagent.

Question 11.
What is Balz – Schiemann reaction?
Answer:
Fluoro benzene is prepared by treating benzene diazonium chloride with fluoro boric acid. This reaction produces diazonium fluoroborate which on heating produces fluorobenzene. This reaction is called Balz – schiemann reaction.
C₆H₅N₂Cl + HBF₄ C₆H₅N₂ + BF₄^– C₆H₅ F + BF₃ + N₂
Benzene diazonium chloride                                          Fluorobenzene

Question 12.
Write the uses of chloro benzene.
Answer:

• Chloro benzene is used in the manufacture of pesticides like DDT
• It is used as high boiling solvent in organic synthesis.
• It is used as fibre – swelling agent in textile processing.

Question 13.
How is ethylidene dichloride prepared from
(i) Acetaldehyde
(ii) Acetylene
Answer:
i) Treating acetaldehyde with PCl₅:
CH₃CHO (Acetaldehyde) + PCl₅ → CH₃CHCl₂ (Ethylidene dichloride) + POCl

ii) Adding hydrogen chloride to acetylene

Question 14.
How is ethylene dichloride prepared from (i) Chloride (ii) PCl₅?
Answer:
i) Addition of chlorine to ethylene

ii) Action of PCl₅ (or HCl) on ethylene glycol

Question 15.
What happens when the following compounds are treated with alcoholic KOH?
i) Ethylidene dichloride
ii) Ethylene dichloride
Answer:
i) Ethylidene dichloride:

ii) Ethylene dichloride:

Question 16.
Write the uses of methylene chloride.
Answer:
Methylene chloride is used as

1. aerosol spray propellant
2. solvent in paint remover
3. process solvent in the manufacture of drugs
4. a metal cleaning solvent

Question 17.
How are the following compounds prepared from chlorobenzene?
i) Benzene
ii) Phenyl magnesium chloride
Answer:
i) C₆H₆ (Benzene):
Chlorbenzene undergoes reduction with Ni – Al alloy in the presence of NaOH gives benzene.
C₆H₅Cl + 2(H) C₆H₆ + HCl
Chloro benzene              Benzeneide

ii) Phenyl Magnesium chloride:
Chloro benzene reacts with magnesium to form phenyl magnesium chloride in tetra hydrofuran (THF).
C₆H₅Cl (Chloro benzene) + Mg C₆H₅MgCl (Phenyl magnesium chloride)

IV. Long question and answers (5 Marks):

Question 1.
Explain the S_N² mechanism of haloalkanes with suitable example.
Answer:
S2 stands for bimolecular nucleophilic substitution
“S” stands for substitution
“N” stands for nucleophilic
“2” stands for bimolecular (two molecules are involved in the rate determining step)
The rate of S_N² reaction depends upon the concentration of both alkyl halide and the nucleophile.
Rate of reaction = k₂ [alkyihalide] [nucleophile]
This S_N² reaction follows second order kinetics and occurs in one step.

This reaction involves the formation of a transition state in which both the reactant molecules are partially bonded to each other. The attack of nucleophile occurs from the back side and the halide ion leaves from the front side. The carbon at which substitution ocurs ha inverted configuration during the course of reaction just as an umbrella has tendency to invert in a wind storm. This inversion of configuration is called Walden inversion; after paul walden who first discovered the inversion of configuration of a compound in S_N² reaction.

We understand S_N² reaction mechanism by taking an example of reaction between chloromethane and aqueous KOH. S_N² reaction of an optically active haloalkane is always accompanied by inversion of configuration at the asymmetric centre.

 

Question 2.
Explain the S_N¹ mechanism of haloalkanes with suitable examples.
Answer:
S_N¹ stands for unimolecular nucleophilic substitution
‘S’ stands for substitution
‘N’ stands for nucleophilic
‘1’ stands for unimolecular (one molecule is involved in the rate determining step)
The rate of the following S_N¹ reaction depends upon the concentration of aikyl halide (RX) and is independent of the concentration of the nucleophile (OH-).
Rate of the reaction = k[alkyl halide]
R – Cl + OH^– → R – OH + Cl^–
This S_N¹ reaction follows first order kinetics and occurs in two steps.
We understand S_N¹ reaction mechanism by taking a reaction between tertiary hutyl bromide with aqueous KOH.

This reaction takes place in two steps aas shown below.

Step – 1:
Formation of carbocation:

t – butyl bromide

The polar C – Br bond breaks forming a carbocation and bromide ion. This step is slow and hence it is the rate determining step.

Step 2:
Nucleophilic attack on carbocation
The carbocation immediately reacts with the nucleophile. This step is fast and hence does not affect the rate of the reactions.

As shown above, the nucleophilic reagent OH~ can attack carbocation from both the sides, they will be mirror image of each other.

In the above example the substrate tert-butyl bromide is not optically active, hence the obtained product is optically inactive. If halo alkane substrate is optically active then, the product obtained will be optically inactive racemic mixture. As nucleophilic reagent OH- can attack carbocation from both the sides, to form equal proportion of dextro and levorotatory optically active isomers which form optically inactive racemic mixture.

Example :
Hydrolysis of optically active 2- bromo butane gives racemic mixture of ±butan-2-ol.

Question 3.
Explain the E₂ reaction mechanism with suitable example.
Answer:
E₂ stands for bimolecular elimination reaction
‘E’ stands for elimination
‘2’ stands for bimolecular
The rate of E₂ reaction depends on the concentration of alkyl halide and base

Rate = k₂ [alkyl halide] [base]
It is therefore, a second-order reaction generally primary alkyl halide undergoes this reaction in the presence of alcoholic KOH. E₂ is a one-step process in which the abstraction of the proton from the p carbon and expulsion of halide from the carbon occurs simultaneously. The mechanism is shown below.

Question 4.
Explain the E₁ reaction mechanism with suitable example.
Answer:
E₁ stands for unimolecular elimination reaction
‘E’ stands for elimination ‘1’ stands for unimolecular
The rate of E₁ reaction depends on the concentration of alkyl halide only and hence
rate = k [alkyl halide]
Generally, tertiary alkyl halide which undergoes elimination reaction by this mechanism in the presence of alcoholic KOH following first order kinetics is a two step process. The mechanism is shown by taking following example.

step – 1:
Heterolytic fission to yield a carbocation:

Step – 2:
Elimination of a proton from the β – carbon to produce an alkene:

Question 5.
How are the following compounds prepared from Methyl magnesium iodide?
(i) Ethanol
(ii) Tert-butyl alcohol
(iii) Acetaldehyde
Answer:
(i) Ethanol:
Formaldehyde reacts with methyl magnesium iodide to give addition products which on hydrolysis yield ethanol.

(ii) Tert-butyl alcohol:
Acetone reacts with methyl magnesium iodide to give an additional product which on hydrolysis yields tert butyl alcohol.

(iii) Acetaldehyde:
Ethyl formate reacts with methyl magnesium iodide and followed by acid hydrolysis, it forms Acetaldehyde.

Question 6.
How is ethylene dichloride converted into
i) Acetaldehyde
ii) Ethylene glycol
ii) Ethylene
Answer:
i) Acetaldehyde:
(Hydrolysis with aqueous NaOH or KOH)
Ethylidene chloride reacts with aqueous KOH to give acetaldehyde.

ii) Ethylene glycol :
Ethylene chloride reacts with aqueous KOH, it gives glycol.

iii) Ethylene:
Ethylene dichloride is heated with Zinc in presence of methanol gives ehtylene.

Question 7.
How are the following compounds prepared from chloroform?
(i) Phosgene
(ii) Methylene chloride
(iii) Methyl isocyanide
Answer:
(i) Phosgene:
Chloroform undergoes oxidation in the presence of light and air to form phosgene (carbonyl chloride)

Since phosgene is very poisonous, its presence makes chloroform unfit for use as an anaesthetic.

(ii) Methylene chloride:
Chloroform undergoes reduction with zinc and HCl in the presence of ethyl alcohol to form methylene chloride.
CHCl₃ (Chloroform) + 2(H) CH₂Cl₂ (Methylene chloride)+ Cl₂

(iii) Methyl isocyanide:
Chloroform reacts with aliphatic or aromatic primary amine and alcoholic caustic potash, to give foul-smelling alkyl isocyanide (carbylamines).
CH₃NH2     +     CHCl₂ + 3KOH → CH₃NC + 3KCl + 3H₂O
Methylamine Chloroform          Methyl isocyanide

Question 8.
Discuss the aromatic electrophilic substitutions reaction of chlorobenzene.
Answer: