[PDF] CBSE NCERT Solutions for Class 12 Chemistry Chapter 10

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Class- XII-CBSE-Chemistry Haloalkanes and Haloarenes

Practice more on Haloalkanes and Haloarenes Page - 1 www.embibe.com CBSE NCERT Solutions for Class 12 Chemistry Chapter 10

Back of Chapter Questions

1.Write structure of the following compounds:

(i)2-chloro-3-methypentane (ii)1-chloro-4-ethylcylohexane (iii)4-tert, Buytl-3-iodoheptane (iv)1,4-Dibromobut-2-ene (i)2-chloro-3-methyl pentane

Parent-Carbon Chain = 5 membered (pent)

Prefix ൌ Chloro (െ

(ii)1-chloro-4-ethylcyclohexane

Parent-Carbon Chain ൌ Cyclopent

Primary Prefix ൌ Chloro (-)

Primary suffix ൌ ane

(iii)4-tert-Butyl-3-iodoheptane Class- XII-CBSE-Chemistry Haloalkanes and Haloarenes Practice more on Haloalkanes and Haloarenes Page - 2 www.embibe.com

Parent-Carbon Chain = 7 (hept)

Primary Prefix = െ (Iodo)

Substituent ՜

Primary suffix ൌ ane

(iv) 1,4-Dibromobut-2-ene

Primary Prefixൌെ (Bromo)

Parent-Carbon Chain ൌ͹ (bute)

Primary suffix ൌene

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

Primary Prefix ൌെ (Bromo)

Substituent ՜ െଷ (methyl) and െȁെെ (Secondary butyl)

Primary suffix = ane

Class- XII-CBSE-Chemistry Haloalkanes and Haloarenes

Practice more on Haloalkanes and Haloarenes Page - 3 www.embibe.com 2. Why is sulphuric acid not used during the reaction of alcohols with KI?

Solution:

Thus, the reaction between alcohol and HI to form an alkyl iodide cannot occur. Hence, sulphuric acid is not used during the reaction of alcohols with KI. Instead, a non-oxidizing acid such as ଷସ is used.

3. Write structures of different dihalogen derivates of propane.

Solution:

There are four different dihalogen derivatives of propane. The structure of these derivatives are shown below. (i)

1,1-Dibromopropane

(ii)

2,2-Dibromopropane

(iii)

1,2-Dibromopropane

(iv) Class- XII-CBSE-Chemistry Haloalkanes and Haloarenes Practice more on Haloalkanes and Haloarenes Page - 4 www.embibe.com 1,3-Dibromopropane photochemical chlorination yields (i) A single monochloride (ii) Three isomeric monochlorides. (iii) Four isomeric monochlorides.

Solution:

(i) Only one type of hydrogen atom in the isomer of the alkane of the molecular because the replacement of any hydrogen atom leads to the formation of the same product. Thus the isomer is neopentane.

Neopentane

three different types of H-atoms to have three isomeric monochlorides. Thus, the isomer is n-pentane. The three types of H atoms are labelled as a, b and c. types of H-atoms to have four isomeric monochlorides. Thus, the isomer is 2-methylbutane. The four types of H-atoms are labelled as a,b,c and d.

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

Class- XII-CBSE-Chemistry Haloalkanes and Haloarenes Practice more on Haloalkanes and Haloarenes Page - 5 www.embibe.com (i) (ii) (iii) (iv) (v) ൅՜ (vi)

Solution:

(i) (ii) Class- XII-CBSE-Chemistry Haloalkanes and Haloarenes Practice more on Haloalkanes and Haloarenes Page - 6 www.embibe.com (iv) v (v) (vi)

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

(i) Bromomethane, Bromoform, Chloromethane, Dibromomethane. (ii) 1- Chloropropane, Isopropyl chloride, 1-Chlorobutane.

Solution:

For alkyl halides having the same alkyl group, the boiling point increases with an increase in the atomic mass of the halogen atom. Also, for alkyl halides having the same alkyl group, the boiling point increases with an incr ease in the number of ha lide s. Th erefore , the boiling point of Therefore, the given compounds can be arranged in the order of their increasing boiling points as Class- XII-CBSE-Chemistry Haloalkanes and Haloarenes

Practice more on Haloalkanes and Haloarenes Page - 7 www.embibe.com 7. Which alkyl halide from the following pairs would you expect to react more rapidly

by an ୒ʹ mechanism? Explain your answer. (i) (ii) (iii)

Solution:

(i)

Rate of ୒ʹ ן

ʹെbromobutane is a ʹ୭ alkylhalide whereas ͳെbromobutane is a ͳ୭ alkyl

halide. The a pproach ing of nucleophile is more hindere d in ʹെbromobutane than in ͳെbromobutane. Therefor e, ͳെbromobutane reacts more rapidly than ʹെbromobutane by an ୒ʹ mechanism. (ii)

Rate of ୒ʹ ן

Class- XII-CBSE-Chemistry Haloalkanes and Haloarenes

Practice more on Haloalkanes and Haloarenes Page - 8 www.embibe.com ʹെbromobutane is ʹ୭ alkyl halide whereas ʹെbromoെʹെmethylpropane

is ͵୭ alkyl halide. Thus, greater numbers of substituents are present in ͵୭ alkyl halide than in ʹ୭ alkyl halide for hindering the approaching nucleophile. Therefore, ʹെbromobutane re acts more rapidl y than 2 -bromo-2- methylpropane by an ୒ʹ mechanism. (iii) ʹെmethylെͳെbromobutane is Ⱦ substituted methyl group. So, it is more hindered as compared to 3-methyl-1-bromobutane. Therefore, ୒ʹ reaction rate will be higher in ͵െmethylെͳെbromobutane.

8. In the following pairs of halogen compounds, which compound undergoes faster

୒ͳ reaction? (i) and (ii) and

Solution:

(i) Class- XII-CBSE-Chemistry Haloalkanes and Haloarenes Practice more on Haloalkanes and Haloarenes Page - 9 www.embibe.com ୒ͳ reaction proceeds via the formation of carbocation. The alkyl halide (i) is ͵୭

while (ii) is ʹ୭. Therefore, (I) forms ͵୭ carbocation while (II) forms ʹ୭

Carbocation. Greater the stability of the carbocation, faster is the rate of ୒ͳ reaction. ͵୭ carbocation is more stable due to 9 hyperconjugation and more ൅ effect of ͵െଷ group ʹ୭ carbocation formed has 4 hyperconjugation and ʹെ Therefore, (I), i.e. 2-chloro-2-methylpropane, undergoes faster ୒ͳ reaction than (ii) i.e., 3-chloropentane. (ii)

The alkyl halide (i) is ʹ୭ while (ii) is ͳ୭ǡʹ୭ carbocation is more stable than ͳ୭

carbocation because in ʹ୭ carbocation 4 hyperconjugations are taking are taking place & +I effect of െହଵଵ group. Therefore (I), 2-chloroheptane, undergoes faster ୒ͳ reaction than (II), 1-chlorohexane.

9. Identify A, B, C, D, E, R and ଵ in the following:

Class- XII-CBSE-Chemistry Haloalkanes and Haloarenes Practice more on Haloalkanes and Haloarenes Page - 10 www.embibe.com

Solution:

MgBr is attached, Hence C is

Therefore, the compound

will form when react with alkyl halide. Hence R is Class- XII-CBSE-Chemistry Haloalkanes and Haloarenes Practice more on Haloalkanes and Haloarenes Page - 11 www.embibe.com When an alkyl halide is treated with Na in the presence of dry ether, a hydrocarbon containing double the number of carbon atoms as present in the original halide is obtained as the product. This reaction is known as Wurtz reaction. Therefore, the halide, ଵെǡ is

And, compound E is

Class- XII-CBSE-Chemistry Haloalkanes and Haloarenes Practice more on Haloalkanes and Haloarenes Page - 12 www.embibe.com

Page No.310

1. Name the following halides according to IUPAC system and classify them as alkyl,

allyl, benzyl (primary, secondary, tertiary), vinyl or aryl halides: Class- XII-CBSE-Chemistry Haloalkanes and Haloarenes Practice more on Haloalkanes and Haloarenes Page - 13 www.embibe.com Solution: (i)

Substituent ൌെଷ (Methyl)

Secondary prefix ൌെ (Chloro)

Primary Suffix ൌ ane

IUPAC name ൌ Secondary prefix ൅ Primary prefix ൅ Word root ൅ primary suffix ൅ secondary suffix IUPAC name is ʹെChloroെ͵െmethylbutane (secondary alkyl halide). (ii)

Substituent ൌെଷ (Methyl)

Secondary prefix ൌെ (Chloro)

(Word root) Parent Carbon chain ൌ͸ (hex)

Primary Suffix ൌ ane

IUPAC name ൌ Secondary prefix ൅ Primary prefix ൅ Word root ൅ primary suffix ൅ secondary suffix (iii)

Substitute ൌെଷ (Methyl)

Secondary prefix ൌെ (Iodo)

Class- XII-CBSE-Chemistry Haloalkanes and Haloarenes

Primary Suffix ൌ ane

IUPAC name ൌ Secondary prefix ൅ Primary prefix ൅ Word root ൅ primary suffix ൅ secondary suffix IUPAC name is ͳെെʹǡʹെdimethylbutane (primary alkyl halide). (iv)

Substitute ൌെଷ (Methyl)

Secondary prefix ൌെ (Bromo)

Primary Suffix ൌane

IUPAC name ൌ Secondary prefix ൅ Primary prefix ൅ Word root ൅ primary suffix ൅ secondary suffix (secondary benzyl halide) (v)

Substitute ൌെଷ (Methyl)

Secondary prefix ൌെ (Bromo)

(Word root) Parent Carbon chain = 4 (but)

Primary Suffix = ane

IUPAC name = Secondary prefix + Primary prefix + Word root + primary suffix + secondary suffix (secondary alkyl halide) (vi) Class- XII-CBSE-Chemistry Haloalkanes and Haloarenes Practice more on Haloalkanes and Haloarenes Page - 15 www.embibe.com

Secondary prefix ൌെ (Bromo)

Primary Suffix ൌ ane

IUPAC name ൌ Secondary prefix ൅ Primary prefix ൅ Word root ൅ primary suffix + secondary suffix (primary alkyl halide) (vii)

Substitute െଷ (Methyl)

Secondary prefix ൌെ (Chloro)

(Word root) Parent Carbon chain ൌͷ (pent)

Primary Suffix ൌ ane

IUPAC name ൌ Secondary prefix ൅ Primary prefix ൅ Word root ൅primary suffix ൅ secondary suffix (Tertiary alkyl halide) (viii)quotesdbs_dbs12.pdfusesText_18

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