Chemistry

Alcohols, Phenols and Ethers

Question:

Write the mechanism of the reaction of HI with methoxybenzene.

Answer:

In case of alkyl aryl ethers, the products are always phenol and an alkyl halide because due to resonance C6H5 – O bond has partial double bond character.
ncert-exemplar-problems-class-12-chemistry-alcohols-phenols-ethers-59

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Alcohols, Phenols and Ethers

Q 1.

The carbon-oxygen bond in phenol is slightly stronger than that in methanol. Why?

Q 2.

Assertion (A): Boiling points of alcohols and ethers are high.
Reason (R): They can form intermolecular hydrogen bonding.

Q 3.

What happens when benzene diazonium chloride is heated with water?

Q 4.

Explain why is OH group in phenols more strongly held as compared to OH group in alcohols.

Q 5.

Explain a process in which a biocatalyst is used in industrial preparation of a compound known to you.

Q 6.

Name the enzymes and write the reactions involved in the preparation of ethanol from sucrose by fermentation.

Q 7.

Give reason for the higher boiling point of ethanol in comparison to methoxymethane.

Q 8.

Arrange the following compounds in decreasing order of acidity:
H2O, R-OH, HC = CH

Q 9.

Explain why are low molecular mass alcohols soluble in water?

Q 10.

Show how would you synthesise the following alcohols from appropriate alkanes?
ncert-solutions-for-class-12-chemistry-alcohols-phenols-and-ether-42

Q 11.

Assertion (A): Bond angle in ethers is slightly less than the tetrahedral angle. Reason (R): There is a repulsion between the two bulky (-R) groups.

Q 12.

Which of the following species can act as the strongest base?
ncert-exemplar-problems-class-12-chemistry-alcohols-phenols-ethers-12

Q 13.

When phenol is treated with bromine water, white precipitate is obtained. Give the structure and the name of the compound formed.

Q 14.

Assertion (A): Ethanol is a weaker acid than phenol.
Reason (R): Sodium ethoxide may be prepared by the reaction of ethanol with aqueous NaOH.

Q 15.

Classify the following as primary, secondary and tertiary alcohols.
ncert-solutions-for-class-12-chemistry-alcohols-phenols-and-ether-1
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Q 16.

Which of the following compounds are/is aromatic alcohol?  
ncert-exemplar-problems-class-12-chemistry-alcohols-phenols-ethers-6

Q 17.

Explain why alcohols and ethers of comparable molecular mass have different boiling points.

Q 18.

Write structures of the compounds whose IUPAC names are as follows:
(i)2-Methylbutan-2-ol
(ii)l-Phcnylpropan-2-ol
(iii)3,5-DimethyIhexane-l,3,5-triol
(iv)2,3-Dicthylphenol
(v)1-Ethoxypropane
(vi)2-Ethoxy-3-methylpentane
(vii) Cyclohexylmethanol
(viii) 3-Cyclohexylpcntan-3-ol
(ix)Cyclopcnt-3-en-l-ol
(x)4-ChIoro-3-ethylbutan-l-ol

Q 19.

Name the factors responsible for the solubility of alcohols in water.

Q 20.

Why is the reactivity of all three classes of alcohols with cone. HCl and ZnCl2 (Lucas reagent) different?

Q 21.

Write the IUPAC name of the compound given below.
ncert-exemplar-problems-class-12-chemistry-alcohols-phenols-ethers-25

Q 22.

Write the structures of the isomers of alcohols with molecular formula C4H10O. Which one of these isomers exhibits optical activity?

Q 23.

Explain why is O = C = O nonpolar while R – O – R is polar.

Q 24.

Explain why is p-nitrophenol more acidic than phenol?

Q 25.

Identify aliylic alcohols in the above examples.

Q 26.

Write the mechanism of the reaction of HI with methoxymethane.

Q 27.

Assertion (A): IUPAC name of the compound
ncert-exemplar-problems-class-12-chemistry-alcohols-phenols-ethers-57
Reason (R): In IUPAC nomenclature, ether is regarded as hydrocarbon derivative in which a hydrogen atom is replaced by -OR or -OAr group [where R = alkyl group and Ar = aryl group]

Q 28.

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

Q 29.

How can propan-2-one be converted into tert-butyl alcohol?

Q 30.

In Kolbe's reaction, instead of phenol, phenoxide ion is treated with carbon dioxide. Why?

Q 31.

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

Q 32.

What is denatured alcohol?

Q 33.

Suggest a reagent for conversion of ethanol to ethanal.

Q 34.

Preparation of alcohols from alkenes involves the electrophilic attack on alkene carbon atom. Explain its mechanism.

Q 35.

Assertion (A): p-Nitrophcnol is more acidic than phenol.
Reason (R): Nitro group helps in the stabilization of the phenoxide ion by dispersal of negative charge due to resonance.

Q 36.

Write the names of reagents and equations for the preparation of the following ethers by Williamson's synthesis:
(i)1-Propoxypropane
(ii)Ethoxybenzene
(iii)2-Methoxy-2-methylpropane
(iv)1-Methoxyethane

Q 37.

Mark the correct increasing order of reactivity of the following compounds with HBr/HCl.
ncert-exemplar-problems-class-12-chemistry-alcohols-phenols-ethers-15

Q 38.

Phenol can be distinguished from ethanol by the reactions with ………….
(a) Br2/water (b) Na
(c) Neutral FeCl3 (d) All of these

Q 39.

Write structures of the products of the following reactions:
ncert-solutions-for-class-12-chemistry-alcohols-phenols-and-ether-11

Q 40.

Give two reactions that show the acidic nature of phenol. Compare its acidity with that of ethanol.

Q 41.

Which of the following reagents can be used to oxidize primary alcohols to aldehydes?
(a) CrO3 in anhydrous medium
(b) KMnO4 in acidic medium
(c) Pyridinium chlorochromate
(d) Heat in the presence of Cu at 573 K

Q 42.

Match the starting materials given in Column I with the products formed by these (Column II) in the reaction with HI.
ncert-exemplar-problems-class-12-chemistry-alcohols-phenols-ethers-50
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Q 43.

Assertion (A): Phenol forms 2,4, 6-tribromophenol on treatment with Br2 in carbon disulphide at 273 K.
Reason (R): Bromine polarizes in carbon disulphide.

Q 44.

Assertion (A): Phenols give o-nitrophenol and p-nitrophenol on nitration with cone. HNO3 and H2SO4 mixture.
Reason (R): -OH group in phenol is o-,p-directing.

Q 45.

Write the mechanism of the reaction of HI with methoxybenzene.

Q 46.

Explain how does the – OH group attached to a carbon of benzene ring activate it towards electrophilic substitution?

Q 47.

Out of o-nitrophenol and o-cresol which is more acidic?

Q 48.

Explain why nucleophilic substitution reactions are not very common in phenols.

Q 49.

What is the correct order of reactivity of alcohols in the following reaction?
ncert-exemplar-problems-class-12-chemistry-alcohols-phenols-ethers-3

Q 50.

Suggest a reagent for the following conversion.
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