Chapter-10 Haloalkanes and Haloarenes

Why are aryl halides less reactive towards nucleophilic substitution reactions
than alkyl halides? How can we enhance the reactivity of aryl halides?

Some halogen containing compounds are useful in daily life. Some compounds
of this class are responsible for exposure of flora and fauna to more and more
of UV light which causes destruction to a great extent. Name the class of these
halocompounds. In your opinion, what should be done to minimise harmful
effects of these compounds.

Some alkylhalides undergo substitution whereas some undergo elimination
reaction on treatment with bases. Discuss the structural features of alkyl
halides with the help of examples which are responsible for this difference.

Match the items of Column I and Column II.
Column I                                                                Column II
(i) SN1 reaction                                                        (a) vic-dibromides
(ii) Chemicals in fire extinguisher                                  (b) gem-dihalides
(iii) Bromination of alkenes                                          (c) Racemisation
(iv) Alkylidene halides                                                (d) Saytzeff rule
(v) Elimination of HX from alkylhalide                            (e) Chlorobromocarbons

Match the the compounds given in Column I with the effects given in Column II.
Column I                                                            Column II
(i) Chloramphenicol                                             (a) Malaria
(ii) Thyroxine                                                     (b) Anaesthetic
(iii) Chloroquine                                                  (c) Typhoid fever
(iv) Chloroform                                                   (d) Goiter
                                                                       (e) Blood substituent

Cyanide ion acts as an ambident nucleophile. From which end it acts as a
stronger nucleophile in aqueous medium? Give reason for your answer.

How can you obtain iodoethane from ethanol when no other iodine containing
reagent except NaI is available in the laboratory?

Discuss the nature of C–X bond in the haloarenes.

Predict the major product formed when HCl is added to isobutylene. Explain
the mechanism involved.

How will you obtain monobromobenzene from aniline?

Elimination reactions (especially β-elimination) are as common as the
nucleophilic substitution reaction in case of alkyl halides. Specify the reagents
used in both cases.

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

Chemistry 144
(I) (II) (III)
59. Write down the structure and IUPAC name for neo-pentylbromide.
60. A hydrocarbon of molecular mass 72 g mol–1 gives a single monochloro
derivative and two dichloro derivatives on photo chlorination. Give the
structure of the hydrocarbon.
61. Name the alkene which will yield 1-chloro-1-methylcyclohexane by its reaction
with HCl. Write the reactions involved.
62. Which of the following haloalkanes reacts with aqueous KOH most easily?
Explain giving reason.
(i) 1-Bromobutane
(ii) 2-Bromobutane
(iii) 2-Bromo-2-methylpropane
(iv) 2-Chlorobutane
63. Why can aryl halides not be prepared by reaction of phenol with HCl in the
presence of ZnCl2?
64. Which of the following compounds would undergo SN1 reaction faster and
why?
(A) (B)
65. Allyl chloride is hydrolysed more readily than n-propyl chloride. Why?
66. Why is it necessary to avoid even traces of moisture during the use of a
Grignard reagent?
67. How do polar solvents help in the first step in SN1 mechanism?
68. Write a test to detect the presence of double bond in a molecule.
69.

Write a test to detect the presence of double bond in a molecule.

How do polar solvents help in the first step in SN1 mechanism?

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

Allyl chloride is hydrolysed more readily than n-propyl chloride. Why?

Why can aryl halides not be prepared by reaction of phenol with HCl in the
presence of ZnCl2?

Which of the following haloalkanes reacts with aqueous KOH most easily?
Explain giving reason.
(i) 1-Bromobutane
(ii) 2-Bromobutane
(iii) 2-Bromo-2-methylpropane
(iv) 2-Chlorobutane

Name the alkene which will yield 1-chloro-1-methylcyclohexane by its reaction
with HCl. Write the reactions involved.

A hydrocarbon of molecular mass 72 g mol–1 gives a single monochloro
derivative and two dichloro derivatives on photo chlorination. Give the
structure of the hydrocarbon.

Write down the structure and IUPAC name for neo-pentylbromide.

Which of the following compounds will have the highest melting point and
why?

Compound ‘A’ with molecular formula C4H9Br is treated with aq. KOH solution.
The rate of this reaction depends upon the concentration of the compound ‘A’
only. When another optically active isomer ‘B’ of this compound was treated
with aq. KOH solution, the rate of reaction was found to be dependent on
concentration of compound and KOH both.
(i) Write down the structural formula of both compounds ‘A’ and ‘B’.
(ii) Out of these two compounds, which one will be converted to the product
with inverted configuration.

Classify the following compounds as primary, secondary and tertiary halides.
(i) 1-Bromobut-2-ene (ii) 4-Bromopent-2-ene
(iii) 2-Bromo-2-methylpropane

Why is the solubility of haloalkanes in water very low?

Which of the following compounds (a) and (b) will not react with a mixture of
NaBr and H2SO4. Explain why?

Discuss the role of Lewis acids in the preparation of aryl bromides and chlorides
in the dark.

Haloarenes are less reactive than haloalkanes and haloalkenes. Explain.

Why iodoform has appreciable antiseptic property?

Out of o-and p-dibromobenzene which one has higher melting point and why?

Aryl chlorides and bromides can be easily prepared by electrophilic
substitution of arenes with chlorine and bromine respectively in the presence
of Lewis acid catalysts. But why does preparation of aryl iodides requires
presence of an oxidising agent?

Why haloalkanes are more reactive than haloarenes.

Why do haloalkenes under go nucleophillic substitution whereas haloarenes      under go electophillic substitution .

When an alkyl halide is treated with ethanolic solution of KCN, the major product is alkyl cyanide where as if alkyl halide is treated with AgCN,the major product is alkyl isocyanide.

How do 10 20 30 alcohols differ in terms of dehydrogenation?

Why are the reaction of alcohol /phenol with acid chloride in the presence of pyridine ?

Explain why o-nitrophenol is more acidic than o-methoxy phenol ?

Aryl halides cannot be prepared by the action of sodium halide in the presence H2SO4 .Why?

Why Grignard reagent should be prepared under an hydrous conditions.?

Why is Sulphuric acid not used during the reaction of alcohols with KI ?

p- dichlorobenzene has highest m.p. than those of ortho and m-isomers.?

Although chlorine is an electron- withdrawing group, yet it is ortho and para directing in electrophillic aromatic substitution reactions.Why

The treatment of alkyl chlorides with aqueous KOH lead to the formation of alcohols but in

presence of alcoholic KOH alkenes are major products. Explain?

Explain why vinyl chloride is unreactive in nucleophillic substitution reaction?

Arrange the following compounds according to reactivity towards nucleophillic substitution reaction with reagents mentioned :-

(i)         4- nitro chloro benzene, 2,4 di nitro chloro bemzene, 2,4,6, trinitrochlorobenzene with

CH3ONa

Which compound will react faster in SN2 reaction with OH---?

Arrange in order of boiling points.

(a)Bromobenzene, Bromoform, chloromethane,Dibromo-methane

(b)1-chloropropane, Isopropyle chloride, 1-Chlorobutane.

Which compound undergoes SN1 reaction first

How can we produce nitro benzene from phenol?

Alcohols reacts with halogen acids to form haloalkenes but phenol does not form halobenzene. Explain

Explain why o-nitrophenol is more acidic than o-methoxy phenol?

Of benzene and phenol, which is more easily nitrated and why?

How will you account for the following? Ethers possess a net dipole moment even if they are symmetrical in structure?

How do 1°, 2° and 3° alcohols differ in terms of their oxidation reaction and dehydrogenation ?

How is diethyl ether prepared from ethyl alcohol?

Why are reactions of alcohol/phenol and with acid chloride in the presence of pyridine?

How the following conversions can be carried out?

(i) Propene to propan-1-ol

(ii) 1-Bromopropane to 2-bromopropane

(iii) Toluene to benzyl alcohol

(iv) Benzene to 4-bromonitrobenzene

(v) Benzyl alcohol to 2-phenylethanoic acid

How the following conversions can be carried out?

(i) Chloro ethane to butane

(ii)Benzene to diphenyl

(iii) tert-Butyl bromide to isobutyl bromide

 (iv) Aniline to phenylisocyanide

What happens when

(i) n-butyl chloride is treated with alcoholic KOH,

(ii) bromobenzene is treated with Mg in the presence of dry ether,

(iii) chlorobenzene is subjected to hydrolysis,

(iv) ethyl chloride is treated with aqueous KOH,

(v) methyl bromide is treated with sodium in the presence of dry ether,

(vi) methyl chloride is treated with KCN.

Primary alkyl halide C₄H₉Br (a) reacted with alcoholic KOH to give compound (b).Compound (b) is reacted with HBr to give (c) which is an isomer of (a). When (a) is reacted with sodium metal it gives compound (d), C₈H₁₈which is different from the compound formed when n-butyl bromide is reacted with sodium. Give the structural formula of (a) and write the equations for all the reactions.

The treatment of alkyl chlorides with aqueous KOH leads to the formation of

alcohols but in the presence of alcoholic KOH, alkenes are major products. Explain.

How the following conversions can be carried out?

(i) Propene to propan-1-ol

(ii) Ethanol to but-1-yne

(iii) 1-Bromopropane to 2-bromopropane

(iv) Toluene to benzyl alcohol

(v) Benzene to 4-bromonitrobenzene

(vi) Benzyl alcohol to 2-phenylethanoic acid

(vii) Ethanol to propanenitrile

(viii) Aniline to chlorobenzene

(ix) 2-Chlorobutane to 3, 4-dimethylhexane

(x) 2-Methyl-1-propene to 2-chloro-2-methylpropane

(xi) Ethyl chloride to propanoic acid

(xii) But-1-ene to n-butyliodide

(xiii) 2-Chloropropane to 1-propanol

(xiv) Isopropyl alcohol to iodoform

(xv) Chlorobenzene to p-nitrophenol

(xvi) 2-Bromopropane to 1-bromopropane

(xvii) Chloroethane to butane

(xviii) Benzene to diphenyl

(xix) tert-Butyl bromide to isobutyl bromide

(xx) Aniline to phenylisocyanide

p-Dichlorobenzene has higher m.p. and lower solubility than those of o- and

m-isomers. Discuss.

Out of C₆H₅CH₂Cl and C₆H₅CHClC₆H₅, which is more easily hydrolysed by aqueous KOH?

Arrange the compounds of each set in order of reactivity towards SN2 displacement:

(i) 2-Bromo-2-methylbutane, 1-Bromopentane, 2-Bromopentane

(ii) 1-Bromo-3-methylbutane, 2-Bromo-2-methylbutane, 3-Bromo-2- methylbutane

(iii) 1-Bromobutane, 1-Bromo-2,2-dimethylpropane, 1-Bromo-2-methylbutane, 1-Bromo-3-methylbutane.

Write the mechanism of the following reaction:

Write the structure of the major organic product in each of the following reactions:

(i) 

(ii) 

(iii) 

(iv) 

(v) 

(vi) 

(vii) 

(viii) 

Give the uses of freon 12, DDT, carbon tetrachloride and iodoform.

Explain why

(i) the dipole moment of chlorobenzene is lower than that of cyclohexyl chloride?

(ii) alkyl halides, though polar, are immiscible with water?

(iii) Grignard reagents should be prepared under anhydrous conditions?

How will you bring about the following conversions?

(i) Ethanol to but-1-yne

(ii) Ethane to bromoethene

(iii) Propene to 1-nitropropane

(iv) Toluene to benzyl alcohol

(v) Propene to propyne

(vi) Ethanol to ethyl fluoride

(vii) Bromomethane to propanone

(viii) But-1-ene to but-2-ene

(ix) 1-Chlorobutane to n-octane

(x) Benzene to biphenyl.

Which compound in each of the following pairs will react faster in S_N2 reaction with OH^-?

(i) CH₃Br or CH₃I

(ii) (CH₃)₃CCl or CH₃Cl

What are ambident nucleophiles? Explain with an example

Write the equations for the preparation of 1-iodobutane from

(i) 1-butanol

(ii) 1-chlorobutane

(iii) but-1-ene.

Write the isomers of the compound having formula C₄H₉Br.

A hydrocarbon C₅H₁₀ does not react with chlorine in dark but gives a single monochloro compound C₅H₉Cl in bright sunlight. Identify the hydrocarbon.

Which one of the following has the highest dipole moment?

(i) CH₂Cl₂

(ii) CHCl₃

(iii) CCl₄

Write the structures of the following organic halogen compounds.

(i) 2-Chloro-3-methylpentane

(ii) p-Bromochlorobenzene

(iii) 1-Chloro-4-ethylcyclohexane

(iv) 2-(2-Chlorophenyl)-1-iodooctane

(v) Perfluorobenzene

(vi) 4-tert-Butyl-3-iodoheptane

(vii) 1-Bromo-4-sec-butyl-2-methylbenzene

(viii) 1,4-Dibromobut-2-ene

Give the IUPAC names of the following compounds:

(i) CH₃CH(Cl)CH(Br)CH₃

(ii) CHF₂CBrClF

(iii) ClCH₂C≡CCH₂Br

(iv) (CCl₃)₃CCl

(v) CH₃C(p-ClC₆H₄)₂CH(Br)CH₃

(vi) (CH₃)₃CCH=CClC₆H₄I-p

Name the following halides according to IUPAC system and classify them as alkyl, allyl, benzyl (primary, secondary, tertiary), vinyl or aryl halides:

(i) (CH₃)₂CHCH(Cl)CH₃

(ii) CH₃CH₂CH(CH₃)CH(C₂H₅)Cl

(iii) CH₃CH₂C(CH₃)₂CH₂I

(iv) (CH₃)₃CCH₂CH(Br)C₆H₅

(v) CH₃CH(CH₃)CH(Br)CH₃

(vi) CH₃C(C₂H₅)₂CH₂Br

(vii) CH₃C(Cl)(C₂H₅)CH₂CH₃

(viii) CH₃CH=C(Cl)CH₂CH(CH₃)₂

(ix) CH₃CH=CHC(Br)(CH₃)₂

(x) p-ClC₆H₄CH₂CH(CH₃)₂

(xi) m-ClCH₂C₆H₄CH₂C(CH₃)₃

(xii) o-Br-C₆H₄CH(CH₃)CH₂CH₃

Identify A, B, C, D, E, R and R1in the following:

In the following pairs of halogen compounds, which compound undergoes faster SN1 reaction?

(i)

(ii)

Which alkyl halide from the following pairs would you expect to react more rapidly by an SN2 mechanism? Explain your answer.

(i)

(ii)

(iii)

Arrange each set of compounds in order of increasing boiling points.

(i) Bromomethane, Bromoform, Chloromethane, Dibromomethane.

(ii) 1-Chloropropane, Isopropyl chloride, 1-Chlorobutane.

:  

Draw the structures of major monohalo products in each of the following reactions:

(i)

(ii)

(iii)

(iv)

(v)

(vi)

Among the isomeric alkanes of molecular formula C₅H₁₂, identify the one that on photochemical chlorination yields

(i) A single monochloride.

(ii) Three isomeric monochlorides.

(iii) Four isomeric monochlorides.

Write structures of different dihalogen derivatives of propane

Why is sulphuric acid not used during the reaction of alcohols with KI?

Write structures of the following compounds:

(i) 2-Chloro-3-methylpentane

(ii) 1-Chloro-4-ethylcyclohexane

(iii) 4-tert. Butyl-3-iodoheptane

(iv) 1,4-Dibromobut-2-ene

(v) 1-Bromo-4-sec. butyl-2-methylbenzene