Alcohols, Phenols And Ethers Class 12th Chemistry Part Ii CBSE Solution

Class 12^th Chemistry Part Ii CBSE Solution

Intext Questions Pg-317

1. Classify the following as primary, secondary and tertiary alcohols:…
2. H2C = CH - CH2OH Classify the following as primary, secondary and tertiary alcohols:…
3. CH3 - CH2 - CH2 - OH Classify the following as primary, secondary and tertiary alcohols:…
4. Classify the following as primary, secondary and tertiary alcohols:…
5. Classify the following as primary, secondary and tertiary alcohols:…
6. Classify the following as primary, secondary and tertiary alcohols:…
7. Identify allylic alcohols in the above examples.

Intext Questions Pg-320

1. Name the following compounds according to IUPAC system.(i) (ii) (iii) (iv) (v)…

Intext Questions Pg-325

1. Show how are the following alcohols prepared by the reaction of a suitable Grignard…
2. Show how are the following alcohols prepared by the reaction of a suitable Grignard…
3. Write structures of the products of the following reactions:
4. Write structures of the products of the following reactions:
5. Write structures of the products of the following reactions:

Intext Questions Pg-335

1. Give structures of the products you would expect when each of the following alcohol reacts…
2. Predict the major product of acid catalyzed dehydration of (i) 1-methyl cyclohexanol and…
3. Ortho and para nitrophenols are more acidic than phenol. Draw the resonance structures of…
4. Reimer - Tiemann reaction Write the equations involved in the following reactions:…
5. Kolbe’s reaction Write the equations involved in the following reactions:…

Intext Questions Pg-342

1. Write the reactions of Williamson synthesis of 2-ethoxy-3-methyl pentane starting from…
2. Which of the following is an appropriate set of reactants for the preparation of…
3. CH3 - CH2 - CH2 - O - CH3 + HBr → Predict the products of the following reactions:…
4. Predict the products of the following reactions:
5. Predict the products of the following reactions:
6. Predict the products of the following reactions:

Exercises

1. Write IUPAC names of the following compounds:
2. Write IUPAC names of the following compounds:
3. Write IUPAC names of the following compounds:
4. Write IUPAC names of the following compounds:
5. Write IUPAC names of the following compounds:
6. Write IUPAC names of the following compounds:
7. Write IUPAC names of the following compounds:
8. Write IUPAC names of the following compounds:
9. Write IUPAC names of the following compounds:
10. C6H5-O-C2H5 Write IUPAC names of the following compounds:
11. C6H5-O-C7H15(n-) Write IUPAC names of the following compounds:
12. Write IUPAC names of the following compounds:
13. 2-Methylbutan-2-ol Write structures of the compounds whose IUPAC names are as follows:…
14. 1-Phenylpropan-2-ol Write structures of the compounds whose IUPAC names are as follows:…
15. 3,5-Dimethylhexane -1, 3, 5-triol Write structures of the compounds whose IUPAC names are…
16. 2,3 - Diethylphenol Write structures of the compounds whose IUPAC names are as follows:…
17. 1 - Ethoxypropane Write structures of the compounds whose IUPAC names are as follows:…
18. 2-Ethoxy-3-methylpentane Write structures of the compounds whose IUPAC names are as…
19. Cyclohexylmethanol Write structures of the compounds whose IUPAC names are as follows:…
20. 3-Cyclohexylpentan-3-ol Write structures of the compounds whose IUPAC names are as…
21. Cyclopent-3-en-1-ol Write structures of the compounds whose IUPAC names are as follows:…
22. 4-Chloro-3-ethylbutan-1-ol. Write structures of the compounds whose IUPAC names are as…
23. Draw the structures of all isomeric alcohols of molecular formula C5H12O and give their…
24. Classify the isomers of alcohols in question 3. (i) as primary, secondary and tertiary…
25. Explain why propanol has higher boiling point than that of the hydrocarbon, butane?…
26. Alcohols are comparatively more soluble in water than hydrocarbons of comparable molecular…
27. What is meant by the hydroboration-oxidation reaction? Illustrate it with an example.…
28. Give the structures and IUPAC names of monohydric phenols of molecular formula, C7H8O.…
29. While separating a mixture of ortho and para nitrophenols by steam distillation, name the…
30. Give the equations of reactions for the preparation of phenol from cumene.…
31. Write chemical reaction for the preparation of phenol from chlorobenzene.…
32. Write the mechanism of hydration of ethene to yield ethanol.
33. You are given benzene, conc. H2SO4 and NaOH. Write the equations for the preparation of…
34. 1-phenylethanol from a suitable alkene. Show how will you synthesise:…
35. cyclohexylmethanol using an alkyl halide by an SN2 reaction. Show how will you synthesise:…
36. pentan-1-ol using a suitable alkyl halide? Show how will you synthesise:…
37. Give two reactions that show the acidic nature of phenol. Compare acidity of phenol with…
38. Explain why is ortho nitrophenol more acidic than ortho methoxyphenol ?…
39. Explain how does the -OH group attached to a carbon of benzene ring activate it towards…
40. Oxidation of propan-1-ol with an alkaline KMnO4 solution. Give equations of the following…
41. Bromine in CS2 with phenol. Give equations of the following reactions:…
42. Dilute HNO3 with phenol. Give equations of the following reactions:…
43. Treating phenol with chloroform in presence of aqueous NaOH Give equations of the…
44. Kolbe’s reaction. Explain the following with an example.
45. Reimer-Tiemann reaction. Explain the following with an example.
46. Williamson ether synthesis. Explain the following with an example.…
47. Unsymmetrical ether Explain the following with an example.
48. Write the mechanism of acid dehydration of ethanol to yield ethene…
49. Propene → Propane-2-ol. How are the following conversions carried out?…
50. Benzyl chloride → Benzyl alcohol. How are the following conversions carried out?…
51. Ethyl magnesium chloride → Propane-1-ol. How are the following conversions carried out?…
52. Methyl magnesium bromide → 2-Methylpropan-2-ol How are the following conversions carried…
53. Oxidation of a primary alcohol to carboxylic acid. Name the reagents used in the following…
54. Oxidation of a primary alcohol to an aldehyde. Name the reagents used in the following…
55. Bromination of phenol to 2,4,6-tribromophenol. Name the reagents used in the following…
56. Benzyl alcohol to benzoic acid. Name the reagents used in the following reactions:…
57. Dehydration of propan-2-ol to propene. Name the reagents used in the following reactions:…
58. Butan-2-one to butan-2-ol. Name the reagents used in the following reactions:…
59. Give a reason for the higher boiling point of ethanol in comparison to methoxymethane.…
60. Give IUPAC names of the following ethers:
61. CH3OCH2CH2Cl Give IUPAC names of the following ethers:
62. O2N-C6H4-OCH3(p) Give IUPAC names of the following ethers:
63. CH3 CH2CH2OCH3 Give IUPAC names of the following ethers:
64. Give IUPAC names of the following ethers:
65. Give IUPAC names of the following ethers:
66. 1-Propoxypropane. Write the names of reagents and equations for the preparation of the…
67. Ethoxybenzene Write the names of reagents and equations for the preparation of the…
68. 2-Methoxy-2-methylpropane Write the names of reagents and equations for the preparation of…
69. 1-Methoxyethane Write the names of reagents and equations for the preparation of the…
70. Illustrate with examples the limitations of Williamson synthesis for the preparation of…
71. How is 1-propoxypropane synthesized from propan-1-ol? Write mechanism of this reaction.…
72. Preparation of ethers by acid dehydration of secondary or tertiary alcohols is not a…
73. 1-propoxypropane Write the equation of the reaction of hydrogen iodide with:…
74. methoxybenzene and Write the equation of the reaction of hydrogen iodide with:…
75. benzyl ethyl ether. Write the equation of the reaction of hydrogen iodide with:…
76. Explain the fact that in aryl alkyl ethers (i) the alkoxy group activates the benzene ring…
77. Write the mechanism of the reaction of HI with methoxymethane.
78. Friedel-Crafts reaction - alkylation of anisole. Write equations of the following…
79. Nitration of anisole. Write equations of the following reactions:…
80. Bromination of anisole in ethanoic acid medium. Write equations of the following…
81. Friedel-Craft’s acetylation of anisole. Write equations of the following reactions:…
82. Show how would you synthesise the following alcohols from appropriate alkenes?…
83. Show how would you synthesise the following alcohols from appropriate alkenes?…
84. Show how would you synthesise the following alcohols from appropriate alkenes?…
85. Show how would you synthesise the following alcohols from appropriate alkenes?…
86. When 3-methylbutan-2-ol is treated with HBr, the following reaction takes place: Give a…

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Intext Questions Pg-317

Question 1.

Classify the following as primary, secondary and tertiary alcohols:

Answer:

It is primary alcohol because carbon which carries the –OH group is only attached to one alkyl group.

Question 2.

Classify the following as primary, secondary and tertiary alcohols:

H₂C = CH – CH₂OH

Answer:

It is primary alcohol because carbon which carries the –OH group is only attached to one alkene group.

Question 3.

Classify the following as primary, secondary and tertiary alcohols:

CH₃ – CH₂ – CH₂ – OH

Answer:

It is primary alcohol because the carbon which carries the –OH group is only attached to one propyl group.

Question 4.

Classify the following as primary, secondary and tertiary alcohols:

Answer:

It is secondary alcohol because the carbon which carries the –OH group is joined directly to methyl and benzene.

Question 5.

Classify the following as primary, secondary and tertiary alcohols:

Answer:

It is secondary alcohol because the carbon which carries the –OH group is joined directly to two different alkyl groups.

Question 6.

Classify the following as primary, secondary and tertiary alcohols:

Answer:

It is tertiary alcohol because the carbon which carries the –OH group is joined directly to three different alkyl groups. Here two of the alkyl group is methyl and the third one is 1-ethylbenzene.

Question 7.

Identify allylic alcohols in the above examples.

Answer:

Allylic alcohol is an organic compound which has the structural formula CH₂ = CHCH₂OH. In other words, in these alcohols, the the-OH group is attached to sp² hybridized carbon next to the carbon-carbon double bond, that is to an allylic carbon. Therefore, in the above examples, the following are the allylic alcohols.

(ii) H₂C = CH – CH₂OH and

(vi)

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Intext Questions Pg-320

Question 1.

Name the following compounds according to IUPAC system.

(i) 

(ii) 

(iii) 

(iv) 

(v) 

Answer:

(i) 3-chloroethyl-2-isopropylpentan-1-ol

(ii) 2,5-Dimethylhexane-1,3-diol

(iii) 3-Bromocyclohexanol

(iv) Hex-1-en-3-ol

(v) 2-Bromo-3-methylbut-2-en-1-ol

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Intext Questions Pg-325

Question 1.

Show how are the following alcohols prepared by the reaction of a suitable Grignard reagent on methanal?

Answer:

In the Grignard reagent reaction, the first step of the reaction is the nucleophilic addition of Grignard reagent to the carbonyl group to form an adduct, Hydrolysis of adduct results in the formation of alcohol.

Here, is the general reaction with Grignard reagent below:-

From here, it is clear that HCHO gives CH₂OH groups, so R of Grignard reagent is the remaining part of given alcohols. Thus, select the suitable Grignard reagent by substituting the value of R. Now we can see the reaction given below:-

Methanal reacts with iso-propyl magnesium bromide, in presence of dry ether gives an additional compound. And this additional compound on reaction with H₂O /H⁺ gives iso-butyl alcohol (i.e., 2-methylpropane-1-ol) as one of the final product.

Question 2.

Show how are the following alcohols prepared by the reaction of a suitable Grignard reagent on methanal?

Answer:

Methanal reacts with cyclohexyl magnesium bromide, in presence of dry ether, which gives an intermediate product. This intermediate product when reacts with given reagent, as shown above, gives cyclohexyl methanol as a product.

Question 3.

Write structures of the products of the following reactions:

Answer:

In this reaction, when propene reacts with the given reagent then the double bond of propene breaks down with charges on them. So, H⁺ gets placed on the carbon which already has two hydrogen atom and OH^- gets substituted on center carbon because it has the more positive charge which attracts OH^-. Thus we get propene-2-or as a product.

Question 4.

Write structures of the products of the following reactions:

Answer:

In this reaction, when Methyl ( 2-oxocyclohexyl) ethanoate reacts with the given reagent then the double bond between the oxygen atom and cyclohexyl gets breaks down, such that O has a negative charge and that particular carbon will have a positive charge on it. So, to neutralize it, H⁺ gets substituted to that carbon and with O^- to form the structure of alcohol. Thus we get Methyl (2-hydroxycyclohexyl) ethanoate as a product.

Question 5.

Write structures of the products of the following reactions:

Answer:

In this reaction, when 2-Methylbutanal reacts with the given reagent NaBH₄, then the double bond between carbon and oxygen gets to break down in the above aldehyde compound, where carbon has positive charge and oxygen will have a negative charge on them. So, H⁺ gets placed on the carbon to complete its octet and H⁺ gets substituted on O^- to form OH, i.e, an alcohol. Thus we get 2-Methylbutan-1-ol as a product.

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Intext Questions Pg-335

Question 1.

Give structures of the products you would expect when each of the following alcohol reacts with

(a) HCl –ZnCl₂

(b) HBr and

(c) SOCl₂.

(i) Butan-1-or (ii) 2-Methylbutan-2-ol

Answer:

(a)

(i) Primary alcohols do no react appreciably with Lucas’ reagent (HCl –ZnCl₂) at room temperature.

(ii) Tertiary alcohol reacts immediately with Lucas ‘reagent.

(b) (i)

(ii) 

(c) (i)

(ii)

Question 2.

Predict the major product of acid catalyzed dehydration of

(i) 1-methyl cyclohexanol and (ii) butan-1-ol

Answer:

Question 3.

Ortho and para nitrophenols are more acidic than phenol. Draw the resonance structures of the corresponding phenoxide ions.

Answer:

Resonating structures of o-nitrophenoxide ions that are formed by the loss of a proton from o-nitrophenol are as follows:

Resonating structures of p-nitrophenoxide ions that are formed by the loss of a proton from p-nitrophenol are as follows:

Resonating structures of phenoxide ions that are formed by the loss of a proton from phenol are as follows:

It is clearly evident from the above structures that due to —R-effect of— NO₂NO₂ group, o-and p-nitrophenoxide ions are more stable than phenoxide ions. Consequently, o- and p-nitrophenols are more acidic than phenols.

Question 4.

Write the equations involved in the following reactions:

Reimer - Tiemann reaction

Answer:

Phenol on mixing with chloroform and NaOH at 340K followed by Acidic hydrolysis, salicyl aldehyde is formed. When carbon tetrachloride (CCl₄) is used at the place of chloroform salicylic acid is formed. This type of reaction is known as Reimer - Tiemann reaction.

Question 5.

Write the equations involved in the following reactions:

Kolbe’s reaction

Answer:

The sodium phenoxide reacts with CO₂ under pressure 4-7 atm at a 400K temperature to form sodium salicylate, which on acidification yields salicylic acid. This type of reaction is known as Kolbe’s reaction.

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Intext Questions Pg-342

Question 1.

Write the reactions of Williamson synthesis of 2-ethoxy-3-methyl pentane starting from ethanol and 3-methyl pentane-2-ol.

Answer:

During Williamson synthesis of ethers, an alkyl halide reacts with an alkoxide(ion with –ve charge on the oxygen of alcohol and + ve charge on alkali metal like Na) ion. it is an S_N2 reaction. In the reaction, alkyl halides should be least hindered. Hence, an alkyl halide is obtained from ethanol and alkoxide ion from 3-methylpentan-2-ol. The reactions are shown below:

Question 2.

Which of the following is an appropriate set of reactants for the preparation of 1-methoxy-4-nitrobenzene and why?

(i) 

(ii) 

Answer:

Set (ii) is appropriate Because CH₃Br is only a nucleophile whereas CH₃ONa is nucleophile as well as strong base, so the elimination reaction can occur,

Question 3.

Predict the products of the following reactions:

CH₃ – CH₂ – CH₂ – O – CH₃ + HBr →

Answer:

When N –propyl methyl ether reacts with HBr, it forms propanol and bromomethane, n-propyl methyl ether will cleave at O . and H⁺ will attack at O, and Br^- will attack CH₃⁺

Question 4.

Predict the products of the following reactions:

Answer:

When Ethoxybenzene Reacts with HBr, it forms Phenol and bromoethane, Ethoxybenzene cleaves at O. H⁺ will attack at O, and Br^- will attack C₂H₅⁺

Question 5.

Predict the products of the following reactions:

Answer:

When nitrating mixture reacts with ethoxy benzene introduction of nitro group is occurred at para position as it will give the stable product without hindrance.

Question 6.

Predict the products of the following reactions:

Answer:

As HI is a strong nucleophile it will protonate the oxygen , to form a good leaving group. And I^- will attack at C(CH₃)₃⁺ to give tert- butyl iodide and ethanol.

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Exercises

Question 1.

Write IUPAC names of the following compounds:

Answer:

2,2,4-Trimethylpentan-3-ol

The naming of the compound usually starts with numbering the carbons in the chain. The lower set of locants are chosen for this purpose, while in this case numbering under this condition is done from the left side. Once the carbons are mentioned, the position of -OH group is numbered and -ol is added as the suffix.

Question 2.

Write IUPAC names of the following compounds:

Answer:

5-Ethylheptane-2,4-diol

Here the longest chain is the straight chain. For such situations, numbering should be such that the functional groups should be denoted by the smallest number. Ethyl group is named at the beginning as it’s a side chain.

Question 3.

Write IUPAC names of the following compounds:

Answer:

Butane-2,3-diol

In this system, glycols are called as Diols and their class name is Alkane diols. The two-hydroxyl group position is indicated by Arabic numerals. Firstly, the carbon chain is named, the -OH positions are numbered and suffixed with -diol (depends on the number of -OH groups.

Question 4.

Write IUPAC names of the following compounds:

Answer:

Propane-1,2,3-triol

Initially carbon chain is named, -OH groups are numbered (can be done from any side as it’s a symmetrical compound) and suffixed with triol.

Question 5.

Write IUPAC names of the following compounds:

Answer:

2-Methylphenol

In the IUPAC system, the position of the substituent w.r.t –OH group is indicated by an Arabic numeral, with the carbon carrying the OH group being numbered 1. So, methyl is numbered at the minimum position and phenol is added. The common name is o-cresol (ortho-cresol).

Question 6.

Write IUPAC names of the following compounds:

Answer:

4-Methylphenol

Methyl group is numbered 4 w.r.t to -OH position. The compound is symmetrical. The compound is known by its common name p-cresol (para cresol).

Question 7.

Write IUPAC names of the following compounds:

Answer:

2,5-Dimethylphenol

The position of the substituent w.r.t –OH group is indicated by an Arabic numeral, with the carbon carrying the OH group being numbered 1. The lowest number chain is further chosen. The positions of the methyl group is 2 and 5.

Question 8.

Write IUPAC names of the following compounds:

Answer:

2,6-Dimethylphenol

The position of the substituent w.r.t –OH group is indicated by an Arabic numeral, with the carbon carrying the OH group being numbered 1. The lowest number chain is further chosen. The positions of the methyl group are 2 and 6 from both sides.

Question 9.

Write IUPAC names of the following compounds:

Answer:

1-Methoxy-2-methylpropane

Longest carbon chain attached to oxygen is chosen. It is called the principal chain and the other carbon chain is named with -oxy(Alkoxy) suffix at the end. Now the position of alkoxy group is 1 w.r.t the principal chain(propane) and the methyl group

Is 2. Further alphabetically methoxy comes before methyl, therefore named as such.

Question 10.

Write IUPAC names of the following compounds:

C₆H₅–O–C₂H₅

Answer:

Ethoxybenzene

The principal chain is benzene, so the short chain is named as ethoxy and suffixed with benzene

Question 11.

Write IUPAC names of the following compounds:

C₆H₅–O–C₇H₁₅(n-)

Answer:

1-Phenoxyheptane

Principal chain is heptane group having 7 carbon groups. Phenol group is called as substituent alkoxy group and is named.

Question 12.

Write IUPAC names of the following compounds:

Answer:

2-Ethoxybutane

The longest chain here is butane and the ethyl group is attached to the 2^nd carbon.

Question 13.

Write structures of the compounds whose IUPAC names are as follows:

2-Methylbutan-2-ol

Answer:

Butane is the longest chain.

Question 14.

Write structures of the compounds whose IUPAC names are as follows:

1-Phenylpropan-2-ol

Answer:

Propane is principle chain and substituents are numbered accordingly.

Question 15.

Write structures of the compounds whose IUPAC names are as follows:

3,5-Dimethylhexane –1, 3, 5-triol

Answer:

Hexane is the longest chain. There are three -OH substituents and 2 methyl groups.

Question 16.

Write structures of the compounds whose IUPAC names are as follows:

2,3 – Diethylphenol

Answer:

-OH of phenol is numbered a 1.

Question 17.

Write structures of the compounds whose IUPAC names are as follows:

1 – Ethoxypropane

Answer:

Propane is the principle chain and the alkoxy group is ethyl group.

Question 18.

Write structures of the compounds whose IUPAC names are as follows:

2-Ethoxy-3-methylpentane

Answer:

Longest chain is pentane and substituents are numbered accordingly.

Question 19.

Write structures of the compounds whose IUPAC names are as follows:

Cyclohexylmethanol

Answer:

In such cases, cyclo groups are named first, followed by conventional naming methods.

Question 20.

Write structures of the compounds whose IUPAC names are as follows:

3-Cyclohexylpentan-3-ol

Answer:

The cyclo group is named first, followed by conventional naming methods.

Question 21.

Write structures of the compounds whose IUPAC names are as follows:

Cyclopent-3-en-1-ol

Answer:

Cyclo group is named first. Pentane having a double bond is named then with the suffix -OL added to the end.

Question 22.

Write structures of the compounds whose IUPAC names are as follows:

4-Chloro-3-ethylbutan-1-ol.

Answer:

The longest chain is butane when looked for minimum numbering case.

Question 23.

Draw the structures of all isomeric alcohols of molecular formula C₅H₁₂O and give their IUPAC names.

Answer:

The structures of all isomeric alcohols of C₅H₁₂O are given below:

(a) 

Naming is done by the conventional method. The -OH group is attached on the first carbon.

(b) 

3-Methylbutan-1-ol

Butane is the longest chain and methyl is the substituent group.

(c) 

3-Methylbutan-1-ol

Longest chain is butane and conventional naming method is used.

(d) 

2,2-Dimethylpropan-1-ol

Isomer is made by transforming the principal carbon into tertiary type. The longest chain is butane and named accordingly.

(e) 

Pentan-2-ol

Longest chain is pentane and the numbering is chosen from the minimum position.

(f) 

3-Methylbutan-2-ol

Butane is the longest chain, further numbering is done by choosing a minimum position for the -OH group followed by other substituents.

(g) 

Pentan-3-ol

Conventional method of naming is used.

(h) 

2-Methylbutan-2-ol

Butane is the longest chain and substituents are named accordingly by looking into minimum position.

Question 24.

Classify the isomers of alcohols in question 3. (i) as primary, secondary and tertiary alcohols.

Answer:

Question 25.

Explain why propanol has higher boiling point than that of the hydrocarbon, butane?

Answer:

Here, propanol undergoes intermolecular H-bonding because of the presence of -OH group while butane has no such property.

(intermolecular Hydrogen bonding in propanol)

Therefore, extra energy will be required to break those hydrogen bonds which in turn causes higher boiling point for propanol when compared to butane.

Question 26.

Alcohols are comparatively more soluble in water than hydrocarbons of comparable molecular masses. Explain this fact.

Answer:

Due to the presence of –OH group, alcohols form hydrogen-bonds with water but hydrocarbons cannot form hydrogen-bonds with water.

Due to inter moleculer hydrogen bonding between Alcohol and water molecular they remain tightly bounded to water molecules and have higher solubility. Whereas in case of hydrocarbon there is no chance of hydrogen bonding.

Question 27.

What is meant by the hydroboration-oxidation reaction? Illustrate it with an example.

Answer:

The hydroboration-oxidation reaction is a two-step reaction that converts an alkene into a neutral alcohol by the net addition of water across the double bond. The hydrogen and hydroxyl group are added in a syn addition leading to the cis configuration. Hydroboration-oxidation is an anti-Markovnikov reaction, with the hydroxyl group attaching to the less substituted carbon. In first step Addition of Hydroborate group is done and in next step, it is oxidized by hydrogen peroxide.

For example: - When propene undergoes hydroboration-oxidation reaction, then it produces propan-1-ol as product. In this reaction diborane i.e., (BH₃)₂ reacts with propene, which in result generates trialkyl borane as an addition product. Then trialkyl borane is oxidised, by using hydrogen peroxide in the presence of aqueous sodium hydroxide to form alcohol, as final product.

Question 28.

Give the structures and IUPAC names of monohydric phenols of molecular formula, C₇H₈O.

Answer:

The different forms of cresol is formed with given molecular formula:

(I) 2-methylphenol

(II) 3-methylphenol

(III) 4-methylphenol

Question 29.

While separating a mixture of ortho and para nitrophenols by steam distillation, name the isomer which will be steam volatile. Give reason.

Answer:

In ortho nitrophenol there is intra-molecular H bonding, whereas in para-nitrophenol there is inter-molecular H bonding, as shown below:

And because of that para-nitrophenol get tightly bounded with water and ortho nitrophenol is steam volatile and it will leave the solution.

Question 30.

Give the equations of reactions for the preparation of phenol from cumene.

Answer:

The conversion of Phenol from Cumene requires the air oxidation of cumene.

The air oxidation of cumene (isopropyl benzene) leads to the production of both phenol and acetone (costlier than phenol).

The air oxidation of cumene gives cumene hydro peroxide as an intermediate which on further hydrolysis (H₃O⁺) gives phenol and acetone.

Question 31.

Write chemical reaction for the preparation of phenol from chlorobenzene.

Answer:

There are many ways to this conversion. Two of them are given below:-

(a) 

In the above conversion, the chlorobenzene is treated with a base such as NaOH, KOH etc. (strong base). The base abstracts the hydrogen from the C-2 position (it can also abstract the hydrogen from the C-6 position, as both are equally acidic) leaving the negative charge at that position.

In the next step Cl^- leaves, leaving behind the positive charge at that carbon. Both the negative charge and positive charge forms a bond resulting Benzyne as the intermediate.

After the formation of the Benzyne intermediate OH^- of the base attacks at the C-1 position and further, the H⁺ attacks to stabilize the negative charge thus resulting in the phenol.

(b) The second method is as follows:

The reaction can start from benzene also. Chlorination of benzene gives Chlorobenzene. When it is further treated with NaOH and H₂O at 350°C it results in the formation of sodium phenoxide which on further treatment H⁺ gives Phenol as the final product.

Question 32.

Write the mechanism of hydration of ethene to yield ethanol.

Answer:

Step 1:- Protonation of ethene to form carbocation by electrophilic attack of H₃O⁺.

Step 2:-Nucleophilic attack of water on carbocation.

Step 3:- Deprotonation to form ethanol.

Question 33.

You are given benzene, conc. H₂SO₄ and NaOH. Write the equations for the preparation of phenol using these reagents.

Answer:

The reaction given below is:

Benzene reacts with concern. H₂SO₄ and undergoes the following mechanism:-

Step 1: The equilibrium produces SO₃ in concentrated H₂SO₄, as shown below:

Step 2: SO₃ is the electrophile which reacts with benzene to form arenium ion, as shown below:

Step 3: A proton is removed from the arenium ion to form benzenesulfonate ion.

Step 4: The benzenesulfonate ion accepts a proton to become benzene-sulphonic acid, as shown below:

Step 5: The benzene sulphonic acid then reacts with NaOH to give phenol as the final product, as shown below:

Question 34.

Show how will you synthesise:

1-phenylethanol from a suitable alkene.

Answer:

1-phenylethanol from a suitable alkene.

The addition of water takes place according to Markovnikov rule. The alkene taken is styrene. And According to the rule, the positive charge i.e. H⁺ goes to the carbon of the double bond which has more number of hydrogens and the negative part i.e. OH- goes to the carbon that has less number of hydrogens. Therefore resulting the final product as 1-phenyl ethanol.

Question 35.

Show how will you synthesise:

cyclohexylmethanol using an alkyl halide by an SN2 reaction.

Answer: