Important Questions for CBSE Class 12 Chemistry – Alcohols, Phenols And Ethers

  

Important Questions for CBSE Class 12 Chemistry –  Alcohols, Phenols And Ethers

PREVIOUS YEARS QUESTIONS

2015

Very Short Answer Type Questions [1 Mark]

Question 1:
Write the IUPAC name of the given compound:

Answer:
2,2-Dimethyl propan-l-ol.

Question 2:
Write the IUPAC name of the given compound:

Answer:
1-Phenyl propan-2-ol.

Question 3:
Write the IUPAC name of the given compound:

Answer:
2,4-Dimethyl phenol.

Question 4:
Write the IUPAC name of the given compound:

Answer:
2-Methyl propane 1, 3-diol.

Question 5:
Write the IUPAC name of the given compound:

Answer:
2-methyl prop-2-en-l-ol.

Question 6:
Write the IUPAC name of the given compound:

Answer:
l-Methoxy-propan-2-ol.

Question 7:
Write the IUPAC name of the given compound:

Answer:
2, 5-Dinitro phenol.

Question 8:
Write the IUPAC name of the given compound:

Answer:

Question 9:
Write the IUPAC name of the given compound:

Answer:
3-methyl but-2-en-l-ol

Short Answer Type Questions [II] [3 Marks]

Question 10:
Give reasons for the following:
(i) p-nitrophenol is more acidic than p-methylphenol.
(ii) Bond length of C—O bond in phenol is shorter than that in methanol.
(iii) (CH3)3C—Br on reaction with sodium methoxide (Na+ _OCH3) gives alkene as the main product and not an ether.
Answer:
(i) Due to -I and -R effect of N03, p-nitrophenoxide ion is more stable than p-methyl phenoxide ions ( + 1 and +R effect of—CH3 group)
(ii) It is due to sp2 hybridization (double bond due to resonance) in phenol than single bond (sp3 hybridization) in methanol.
(iii) Tert. halide undergoes P-elimination reaction with strong nucleophile to form alkene and not ether.

Question 11:
Give reasons for the following:
(i) Phenol is more acidic than ethanol.
(ii) Boiling point of ethanol is higher in comparison to methoxymethane.
(iii) (CH3)3C—O—CH3 on reaction with HI gives CH3OH and (CH3)3C—I as the main products and not (CH3)3 C—OH and CH3I
Answer:
(i) It is because phenoxide ion is more stable than methoxide ion.
(ii) It is because ethanol is associated with intermolecular H-bonding, whereas methoxymethane is not.
(iii) It is because (CH3)3C+ (Tert. carbocation) is more stable, reacts with I- to form tert. butyl iodide.

Question 12:
How do you convert the following:
(i) Aniline to phenol
(ii) Prop-l-ene to Propan- l-ol
(iii) Anisole to 2-methoxytoluene
Answer:

Question 13:
What happens when
(i) ethanol is treated with Cu at 573 K,
(ii) phenol is treated with CH3COCl/anhydrous AlCl3,
(iii) ethyl chloride is treated with NaOCH3?
Answer:

Question 14:
How do you convert the following:
(i) Phenol to 2-hydroxyacetophenone
(ii) Ethyl chloride to methoxy ethane
(iii) Acetone to 2-methylpropan-2-ol
Answer:

Question 15:
How do you convert the following:
(i) Phenol to anisole
(ii) Propan-2-ol to 2-methylpropan-2-ol
(iii) Aniline to phenol
Answer:

Question 16:

Answer:

Question 17:
Give reasons for the following:
(i) Phenol is more acidic than methanol.
(ii) The C—O—H bond angle in alcohols is slightly less than the tetrahedral angle (109°28 ).
(iii) (CH3)3C—O—CH3 on reaction with HI gives (CH3)3C—I and CH3—OH as the main products and not (CH3)3C—OH and CH3—I.
Answer:
(i) It is because phenoxide ions are stabilized by resonance, whereas methoxide ions are not.
(ii) It is due to repulsion between lone pair of electrons with bonded pair of electrons.
(iii) It is because tert. carbocation is more stable which combines with 1“ to form Tert. butyl iodide and methanol.

Question 18:
Give reasons for the following:
(i) O-nitrophenol is more acidic than O-methoxyphenol.
(ii) Butan-l-ol has a higher boiling point than diethylether.
(iii) (CH3)3C—O—CHS on reaction with HI gives (CH3)3C—I and,CH3—OH as the main products and not (CH3)3C—OH and CH3—I
Answer:
(i) O-Nitro phenoxide ion is more stable than O-methoxy phenoxide ion.
(ii) Butan-l-ol is associated with intermolecular H-bonding whereas diethyl ether is not.
(iii) Refer Ans. to Q.17 (iii).

Question 19:
Predict the products of the following reaction:

Answer:

Long Answer Type Questions [5 Marks]

Question 20:
(a) How are following obtained:
(i) Toluene from phenol (ii) Phenol from Aniline.

(c) Give chemical test to distinguish between the following pairs of compound :
(i) Ethanol and phenol
(ii) Methanol and Propan-2-ol.
Answer:

(b) (i) 2-Bromo-3-methyl but-2-en-l-ol.
(ii) 3-Phenoxy heptane.
(c) (i) Add neutral FeCl3. Phenol gives violet colour, ethanol does not.
(ii) Add I2 and NaOH. Propan-2-ol gives yellow ppt of iodoform whereas methanol does not.

2014

Very Short Answer Type Questions [1 Mark]

Question 21:
Which of the following isomers is more volatile: o-nitrophenol or p-nitrophenol?
Answer:
o-nitrophenol is more volatile.

Question 22:

Answer:
Propane 1,2,3-triol

Short Answer Type Questions [I] [2 Marks]

Question 23:
Name the reagents used in the following reactions:
(i) Nitration of phenol to 2, 4, 6-trinitrophenol
(ii) Butanal to Butanol .
(iii) Friedel – Crafts acetylation of anisole
(iv) Oxidation of primary alcohol to aldehyde
Answer:

Question 24:
Name the reagents used in the following reactions:
(i) Bromination of phenol to 2,4,6-tribromophenol
(ii) Butan-2-one to Butan-2-ol
(iii) Friedel – Crafts alkylation of anisoie
(iv) Oxidation of primary alcohol to carboxylic acid.
Answer:

Question 25:
Name the different reagents needed to perform the following reactions:
(i) Phenol to Benzene
(ii) Dehydration of propan-2-ol to propene
(iii) Friedel – Crafts acetylation of anisole
(iv) Dehydrogenation of ethanol to ethanal.
Answer:

Short Answer Type Questions [II] [3 Marks]

Question 26:

Answer:

2013

Very Short Answer Type Questions [1 Mark]

Question 27:
Rearrange the following compounds in the increasing order of their boiling points:
CH3—CHO, CH3—CH2—OH, CH3—CH2—CH3
Answer:
CH3CH2CH3 < CH3CHO < CH3CH2OH.

Question 28:
Arrange the following compounds in the increasing order of their acid strengths:
4-Nitrophenol, Phenol, 2,4,6-Trinitrophenol.
Answer:
Phenol < 4-Nitrophenol < 2, 4, 6-Trinitrophenol.

Short Answer Type Questions [I] [2 Marks]

Question 29:

Answer:

Question 30:
How will you convert:
(i) Propene to Propan-2-ol
(ii) Phenol to 2,4,6-trinitrophenol
Answer:

Question 31:
How will you convert the following?
(i) Propan-2-ol to propanone.
(ii) Phenol to 2,4,6-tribromophenol.
Answer:

Question 32:
How will you convert:
(i) Propene to Propan-l-ol?
(ii) Ethanal to Propan-2-ol?
Answer:

Question 33:

Answer:

Question 34:
Write the equations involved in the following reactions:
(i) Reimer-Tiemann reaction
(ii) Williamson’s ether synthesis.
Answer:
(i) Reimer-Tiemann reaction: Phenols, when treated with chloroform or carbon tetrachloride in presence of aqueous alkali at 340 K, followed by hydrolysis, give o-hydroxybenzaldehyde (salicylaldehyde) and jb-hydroxybenzaldehyde.

(ii) Williamson’s ether synthesis: When alkyl halide reacts with sodium alkoxide, ethers are formed.

Short Answer Type Question [II] [3 Marks]

Question 35:
(a) Explain the mechanism of the following reaction:

(b) Name the reagent used in the oxidation of ethanol to ethanoic acid.
Answer:
(a) Refer Ans. to Q.29.
(b) Acidified KMn04 is used in oxidation of ethanol to ethanoic acid.

2012

Very Short Answer Type Questions [1 Mark]

Question 36:
Draw the structure of hex-l-en-3-ol compound.
Answer:

Question 37:
Draw the structural formula of 2-methylpropan-2-ol molecule
Answer:

Question 38:
Write the IUPAC name of the following compound:

Answer:
Hex-4-en-3-ol

Question 39:
Of the two alcohols (a) CH2=CH—CH2OH and (6) CH2=CH—CH2—CH2OH, which one will react more easily with cone. HCl in the presence of ZnCl2?
Answer:

Question 40:
Write the IUPAC name of the following compound:

Answer:
l-Methoxy-2-methyl propane.

Short Answer Type Questions [I] [2 Marks]

Question 41:
Explain the following terms:
(i) Alcohols are more soluble in water than the hydrocarbons of comparable molecular masses.
(ii) Orthonitrophenol is more acidic than orthomethoxy phenol.
Answer:
(i) Alcohol can form H-bonds with water, whereas hydrocarbon cannot.
(ii) Refer Ans. to Q.18 (i).

Question 42:
Explain the mechanism of acid catalysed hydration of an alkene to form corresponding alcohol.
Answer:

Short Answer Type Questions [II] [3 Marks]

Question 43:
Draw the structure and name the product formed if the following alcohols are oxidized. Assume that an excess of oxidizing agent is used.
(i) CH3CH2CH2CH2OH
(ii) 2-butenol
(iii) 2-methyl-1-propanol
Answer:

Question 44:
State the products of the following reactions:

Answer:

2011

Very Short Answer Type Questions [1 Mark]

Question 45:
How would you convert ethanol to ethene?
Answer:

Question 46:
Draw the structure of 2, 6-dimethylphenol.
Answer:

Question 47:
Give the IUPAC name of the following compound:

Answer:
2-Bromo-3-methyl but-2-ene.

Question 48:
Write the chemical equation for the preparation of phenol from benzene using oleum and sodium hydroxide.
Answer:

Short Answer Type Questions [I] [2 Marks]

Question 49:
How would you obtain
(i) Picric acid (2, 4, 6-trinitrophenol) from phenol,
(ii) 2-Methylpropene from 2-methylpropanol?
Answer:

Question 50:
Explain the following giving one example for each:
(i) Reimer-Tiemann reaction
(ii) Friedel-Crafts acetylation of anisole.
Answer:
(i) Refer Ans. to Q.34 (i).
(ii) Refer Ans. to Q.25 (iii).

Short Answer Type Questions [II] [3 Marks]

Question 51:
Account for the following:
(i) Propanol has higher boiling point than butane.
(ii) Orf/ro-nitrophenol is more acidic than ort/io-methoxyphenol.
(iii) Preparation of ethers by acid dehydration of secondary or tertiary alcohols is not a suitable method.
Answer:
(i) It is because alcohols can form H-bonds with water molecules, whereas hydrocarbons do not.
(ii) It is because — N02 group is electron withdrawing and —OCH3 group is electron releasing. Therefore, o-nitrophenoxide ion is more stable than o-methoxy-phenoxide ion.
(iii) It is because secondary and tertiary alcohols, on dehydration lead to the formation of alkene and not ethers due to the stability of 2° and 3° carbocation.

Question 52:
How would you obtain the following:
(i) Benzoquinone from phenol
(ii) 2-methylpropan-2-ol from methyl magnesium bromide
(iii) Propan-2-ol from propene.
Answer:

Question 53:
Account for the following:
(i) The boiling points of alcohols decrease with increase in branching of the alkyl chain.
(ii) Phenol does not give protonation reaction readily.
(iii) Phenylmethyl ether reacts with HI to give Phenol and Methyl iodide and not Iodobenzene and Methyl alcohol.
Answer:
(i) It is because branched chain alcohols have minimum surface area, therefore, minimum force of attraction, hence, they have lower boiling point.
(ii) It is due to +ve charge on 3 out of 5 resonating structures of phenol. It cannot be protonated easily.
(iii) It is because phenoxide ion is stabilized by resonance, whereas methoxide ion is not.

2010

Very Short Answer Type Questions [1 Mark]

Question 54:
Write the structure of the molecule of a compound whose IUPAC name is l-phenylpropan-2-ol.
Answer:

Question 55:
Write the structure of the following compound: 2-Methyl-2-ethoxypentane.
Answer:

Short Answer Type Questions [I] [2 Marks]

Question 56:
Write the mechanism of the following reactions:
(i) Hydration of ethene to ethanol.
(ii) Dehydration of ethanol, giving ethene.
Answer:
(i) Refer Ans. to Q.42.
(ii) Refer Ans. to Q.33.

Question 57:
Illustrate the following name reactions giving a chemical reaction equation for each:
(i) Kolbe’s reaction of phenol.
(ii) Friedel-Crafts acetylation of anisole.
Answer:

Question 58:
Illustrate the following reactions giving a chemical equation for each:
(i) Kolbe’s reaction.
(ii) Williamson synthesis.

Answer:
(i) Refer Ans. to Q.57 (i).
(ii) Refer Ans. to Q.34 (ii).

Question 59:
Explain the following reactions with an example for each
(i) Reimer-Tiemann reaction.
(ii) Friedel-Crafts reaction.
Answer:
(i) Refer Ans. to Q.34 (i).
(ii) Refer Ans. to Q.25 (iii).

Question 60:

Answer:

Question 61:

Answer:

Short Answer Type Questions [II] [3 Marks]

Question 62:
How would you convert the following:
(i) Phenol to benzoquinone
(ii) Propanone to 2-methylpropan-2-ol
(iii) Propene to propan-2-ol
Answer:

2009

Very Short Answer Type Questions [1 Mark]

Question 63:
Give the IUPAC name of the following compound:

Answer:

Question 64:
Write the structure of the following compound:
2- Methyl-2ethoxypentane
Answer:

Question 65:
Give the IUPAC name of the following compound:

Answer:
2-Bromo-3-methyl but-2-en-l-ol.

Short Answer Type Questions [I] [2 Marks]

Question 66:
Give one chemical test each to distinguish between the following pairs of compounds:
(i) Phenol and Benzoic acid
(ii) 1-Propanol and 2-Propanol
Answer:
(i) Add NaHCO3 to each. Phenol will not react, whereas benzoic acid will give brisk effervescence due to C02.
(ii) Add I2 and NaOH. 2-Propanol will give yellow ppt. of iodoform, whereas 1-propanol will not give yellow ppt.

Question 67:

Answer:

Question 68:

Answer:

Question 69:

Answer:

Short Answer Type Questions [II] [3 Marks]

Question 70:
Explain the mechanism of the following reactions:
(i) Addition of Grignard’s reagent to the carbonyl group of a compound forming an adduct followed by hydrolysis.
(ii) Acid catalysed dehydration of an alcohol forming an alkene.
(iii) Acid catalysed hydration of an alkene forming an alcohol.
Answer:

Question 71:
Explain the following observations:
(i) The boiling point of ethanol is higher than that of methoxymethane.
(ii) Phenol is more acidic than ethanol.
(iii) o- and p-nitrophenols are more acidic than phenol.
Answer:
(i) It is because ethanol is associated with intermolecular H-bonding, therefore, ethanol has higher boiling point than that of methoxymethane which is not associated with intermolecular H-bonding.
(ii) Phenol is more acidic than ethanol because phenoxide ion is more stable due to resonance as compared to ethoxide ion which is unstable due to positive inductive effect of ethyl group.
(iii) It is because —N02 group is electron withdrawing (- R effect), it increases the stability of o- and p-nitrophenoxide ion (phenolate ion) as compared to phenoxide ion.