Chemistry

Haloalkanes and Haloarenes

Question:

Write the mechanism of the following reaction:

ncert-class-12-solutions-chemistry-chapter-10-haloalkanes-haloarenes-27

Answer:

KCN is a resonance hybrid of the following two contributing structures:
ncert-class-12-solutions-chemistry-chapter-10-haloalkanes-haloarenes-14
Thus, CN–   ion is an ambident nucleophile. Therefore, it can attack the “carbon atom of C-Br bond in n-BuBr either through C or N. Since C – C bond is stronger than C – N bond, therefore, attack occurs through C to form n-butyl cyanide.
ncert-class-12-solutions-chemistry-chapter-10-haloalkanes-haloarenes-15

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Haloalkanes and Haloarenes

Q 1.

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

Q 2.

Write the structures and names of the compounds formed when compound ‘A' with molecular formula, C7H8 is treated with Cl2 in the presence of FeCl3.

Q 3.

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

Q 4.

Assertion (A): The boiling points of alkyl halides decrease in the order: RI > RBr > RCl > RF
Reason (R): The boiling points of alkyl chlorides, bromides and iodides are considerably higher than that of the hydrocarbon of comparable molecular mass.

Q 5.

Write the mechanism of the following reaction:

ncert-class-12-solutions-chemistry-chapter-10-haloalkanes-haloarenes-27

Q 6.

Which of the following is halogen exchange reaction?
(a)
ncert-exemplar-problems-class-12-chemistry-haloalkanes-and-haloarenes-7

Q 8.

Assertion (A): It is difficult to replace chlorine by -OH in chlorobenzene in comparison to that in chloroethane.
Reason (R): Chlorine-carbon (C – Cl) bond in chlorobenzene has a partial double bond character due to resonance.

Q 9.

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.

Q 10.

Assertion (A): Nitration of chlorobenzene leads to the formation of m-nitrochlorobenzene.
Reason (R): N02 group is a w-directing group.

Q 11.

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

Q 12.

Arrange each set of compounds in order of increasing boiling points.
(i)Bromomethane, Bromoform, Chloromethane, Dibromomethane.
(ii)1-Chloropropane, Isopropyl chloride, 1-Chlorobutane.

Q 13.

ncert-exemplar-problems-class-12-chemistry-haloalkanes-and-haloarenes-35

Q 14.

ncert-exemplar-problems-class-12-chemistry-haloalkanes-and-haloarenes-36

Q 15.

Ethylene chloride and ethylidene chloride are isomers. Identify the correct statements.  
(a) Both the compounds form same product on treatment with alcoholic KOH
(b) Both the compounds from same product on treatment with aqueous NaOH
(c) Both the compounds form same product on reduction
(d) Both the compounds are optically active

Q 16.

Write structures of the following compounds:
(i) 2-Chloro-3-methylpentane
(ii) 1-Chloro-4-ethylcydohexane
(iii) 4-tert. Butyl-3-iodoheptane
(iv) 1,4-Dibromobut-2-ene
(v) 1-Bromo-4-sec. butyl-2-methylbenzene.

Q 17.

A hydrocarbon C5H10 does not react with chlorine in dark but gives a single monochloro compound C5H9CI in bright sunlight. Identify the hydrocarbon.

Q 18.

Write the isomers of the compound having formula C4H9Br.

Q 19.

Which of the following structure is enantiomeric with the molecule (A) given below:
ncert-exemplar-problems-class-12-chemistry-haloalkanes-and-haloarenes-14

Q 20.

Which of the carbon atoms present in the molecule given below are asymmetric?
ncert-exemplar-problems-class-12-chemistry-haloalkanes-and-haloarenes-30

Q 21.

Alkyl fluorides are synthesized by heating an alkyl chloride/bromide in presence of or
(a) CaF2 (b) CoF2 (c) Hg,F2 (d) NaF

Q 22.

Which of the products will be major product in the reaction given
ncert-exemplar-problems-class-12-chemistry-haloalkanes-and-haloarenes-53

Q 23.

Benzene < Chlorobenzene < Dichlorobenzene < Bromochlorobenzene Arrange the following compounds in increasing order of their boiling points
ncert-exemplar-problems-class-12-chemistry-haloalkanes-and-haloarenes-11
ncert-exemplar-problems-class-12-chemistry-haloalkanes-and-haloarenes-12

Q 24.

ncert-exemplar-problems-class-12-chemistry-haloalkanes-and-haloarenes-33

Q 25.

Haloalkanes contain halogen atom(s) attached to sp3 hybridised carbon atom of an alkyl group. Identify haloalkane from the following compounds.
(a) 2-Bromopentane (b) Vinyl chloride (chloroethene)
(c) 2-Chloroacetophenone (d) Trichloromethane

Q 26.

Draw other resonance structures related to the following structure and find out whether the functional group present in the molecule is ortho, para directing or meta directing.
ncert-exemplar-problems-class-12-chemistry-haloalkanes-and-haloarenes-54

Q 27.

Aryl halides are extremely less reactive towards nucleophilic substitution. Predict and explain the order of reactivity of the following compounds towards nucleophilic substitution:
ncert-exemplar-problems-class-12-chemistry-haloalkanes-and-haloarenes-75

Q 28.

Assertion (A): In monohaloarenes, further electrophilic substitution occurs at ortho and para positions.
Reason (R): Halogen atom is a ring deactivator.

Q 29.

Consider the following reaction and answer the questions
ncert-exemplar-problems-class-12-chemistry-haloalkanes-and-haloarenes-37

Which of the statements are correct about above reaction?
(a) Both (i) and (v) are nucleophiles
(b) In (iii), carbon atom is sp3 hybridised
(c) In (iii), carbon atom is sp2  hybridised
(d) Both (i) and (v) are electrophiles

Q 30.

Which of the following compounds can be classified  as aryl  halides ? (a) p-ClC6H4CH2CH(CH3)2 (b) p-CH3CHCl(C6H4)CH2CH3  (c) o-BrH2CC6H4CH(CH3)CH2CH3 (d) C6H5Cl

Q 31.

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

Q 32.

How will you obtain monobromobenzene from aniline?

Q 33.

Assertion (A): KCN reacts with methyl chloride to give methyl isocyanide Reason (R): CN–  is an ambident nucleophile.

Q 34.

In the following pairs of halogen compounds, which compound undergoes faster SN1  reaction?
ncert-class-12-solutions-chemistry-chapter-10-haloalkanes-haloarenes-10

Q 35.

Identify A, B, C, D, E, R and  R1 in the following:
ncert-class-12-solutions-chemistry-chapter-10-haloalkanes-haloarenes-13

Q 36.

What are ambident nucleophiles ? Explain with an example.

Q 37.

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

Q 38.

Which of the following alcohol will yield the corresponding alkyl chloride on reaction with concentrated HCl at room temperature?
ncert-exemplar-problems-class-12-chemistry-haloalkanes-and-haloarenes-3

Q 39.

Which of the following is an example of vie-dihalide?
(a) Dichloromethane (b) 1, 2-dichloroethane
(c) Ethylidene chloride (d) Allyl chloride

Q 40.

The reaction of toluene with chloride in the presence of iron and in the absence of light yields
>ncert-exemplar-problems-class-12-chemistry-haloalkanes-and-haloarenes-24

Q 41.

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

Q 42.

In the following questions, a statement of Assertion (A) followed by a statement of Reason (R) is given. Choose the correct option out of the choices given below each question:
(a)Assertion and Reason both are correct and Reason is the correct explanation of Assertion.
(b)Assertion and Reason both are wrong.
(c)Assertion is correct but Reason is wrong.
(d)Assertion is wrong but Reason is correct.
(e)Assertion and Reason both are correct statements but Reason is not the correct explanation of Assertion.

Assertion (A): Phosphorus chlorides (tri and penta) are preferred over thionyl chloride for the preparation of alkyl chlorides from alcohols.
Reason (R): Phosphorus chlorides give pure alkyl halides.

Q 43.

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)CI
(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(CI)CH2CH(CH3)2
(ix)CH3CH=CHC(Br)(CH3)2
(x)P-CIC6H4CH2CH(CH3)2
(xi)m-ClCH2C6H4CH2C(CH3)3
(xii)o-Br -C6H4CH (CH3)CH2CH3

Q 44.

Which reagent will you use for the following reaction?
ncert-exemplar-problems-class-12-chemistry-haloalkanes-and-haloarenes-8

Q 45.

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

Q 46.

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

Q 47.

Assertion (A): tert-Butyl bromide undergoes Wurtz reaction to give 2, 2, 3, 3-tetramethylbutane.
Reason (R): In Wurtz reaction, alkyl halides react with sodium in dry ether to give hydrocarbon containing double the number of carbon atoms present in the halide.

Q 48.

Which one of the following has the highest dipole moment?
(i)CH3CI2 (ii) CHCl3 (iii) CCI4

Q 49.

Write the equations for the preparation of 1-iodoobutanefrom (i)1-butanol (ii)1-chlorobutane (iii) but-l-ene.

Q 50.

Why has iodoform appreciable antiseptic property?