Alcohols, Phenols and Ethers Important Questions

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Very Short Answer Questions (1 Mark Questions)

Ques. Phenol reacts with bromine in CS₂ at low temperature to give;

1. 2,4,6-tribromophenol
2. o-and p-bromophenol
3. m-bromophenol
4. p-bromophenol

Ans. (b) o- and p-bromophenol.

Ques. Phenol on reduction with H₂ in the presence of Ni catalyst gives

1. toluene
2. cyclohexane
3. Cyclohexanol
4. benzene

Ans. (c) cyclohexanol

Ques. The compound obtained by the reaction of ethene with diborane followed by hydrolysis with alkaline H₂O₂ is

1. ethanol
2. propanol
3. triethyl bromide
4. toluene

Ans. (a) Ethanol

Ques. Which of the following is formed when glycerol is heated with oxalic acid at 503K?

1. Methanoic acid
2. Acrolein
3. Glyceric acid
4. Allyl alcohol

Ans. (d) Allyl alcohol

Ques. Which of the alcohol does not react with Lucas reagent?

1. n-butanol
2. tert-butyl alcohol
3. sec-butyl alcohol
4. isobutyl alcohol

Ans. (a) n-butanol

Ques. How many alcohols with the molecular formula C₄H₁₀O are chiral?

1. 1
2. 2
3. 3
4. 4

Ans. (a) (1)

Ques. The process of converting alkyl halides into alcohols involves_____________.

1. rearrangement reaction
2. substitution reaction
3. dehydrohalogenation reaction.
4. addition reaction.

Ans. (B) substitution reaction

Ques. Phenol reacts with bromine in CS₂ at low temperature to give

1. 2,4,6-tribromophrnol
2. M-bromophenol
3. 2,4-dibromophenol
4. o- and p-bromophenol

Ans. (A) 2,4,6-tribromophenol

Ques. Phenol on reduction with H₂in the presence of Ni catalyst gives

1. Cyclohexanol
2. cyclohexane
3. toluene
4. benzene

Ans. (a) cyclohexanol

Ques. Dehydration of alcohol is an example of

1. elimination reaction
2. additional reaction
3. substitution reaction
4. redox reaction

Ans. (b) Addition reaction.

Ques. Which of the following is formed when phenol is exposed to air?

1. o-and p-Benzoquinone
2. p-Benzoquinone
3. o-Benzoquinone
4. Phenoquinone

Ans. (a) o- and p-Benzoquinone

Ques. Which of the following reagents cannot be used to oxidize primary alcohols to aldehydes?

1. Heat in the presence of Cu at 573 K
2. Pyridinium chlorochromate
3. CrO₃ in anhydrous medium
4. KMnO₄ in acidic medium

Ans. d KMnO₄ in an acidic medium

Ques. Which alcohols will give the most stable carbocation during dehydration?

Ans. 2-methyl-2-propanol will give the most stable carbocation during dehydration.

Ques. A compound X with the molecular formula C₂H₈O can be oxidised to another compound Y whose molecular formulae is C₃H₆O₂. The compound X maybe?

Ans. CH₃CH₂CH₂OH

Ques. What happens when tertiary butyl alcohol is passed over heated copper at 300°C?

Ans. 2-methoprene is formed when tertiary butyl alcohol is heated over copper at 300 degrees c.

Ques. The decreasing order of boiling point of the following alcohols is

Ans. Pentan-1-ol > 3-methylbutan-2-ol > 2-methylbutan-2-ol .

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Short Answer Questions ( 2 Marks Questions )

Ques. List down the name of the alcohol that is used to make the following ester

Ans. The alcohol used in the preparation of the above ester is Props-2-ol

Ques. Write down the IUPAC name of the given compound

Ans. The IUPAC name of the compound is 2, 5-dinitrophenol.

Ques. How will you convert ethanol to ethene?

Ans. ethanol to ethene can be converted by the following chemical reaction

Ques. Ortho-nitrophenol is more acidic than Ortho-methoxyphenol, Why?

Ans. The methoxy group is the electron-donating group while NO₂ is the electron-withdrawing group in nature, hence the release of H⁺ is easier from O-nitrophenol while it is difficult from methoxy phenol.

Ques. What happens when phenol is treated with bromine water?

Ans. When Phenol is treated with bromine water, 2-4-6-tribromophenol is formed as a product.

Ques. Write the IUPAC name of the following?

Ans. IUPAC Name is- 2-Bromo-3-Methyl-but02-ene-1-ol

Ques. Give the IUPAC name of

Ans. Hex-1-en-2-ol OR 3-Hexanol

Ques. An unknown alcohol is treated with a “Lucas reagent” to determine whether the alcohol is primary, secondary or tertiary. Which alcohol reacts fastest and by what mechanism?

Ans. Lucas test is used to differentiate between primary, secondary and tertiary alcohols. The test is based on alcohols reactivity with hydrogen halides. tertiary alcohol reacts fastest with the sn₁ mechanism.

Ques. Which alcohol reacts most readily with Lucas reagent?
Ans. Tertiary alcohols react fastest with Lucas’s reagent. Tertiary alcohol reacts easily at room temperature and shows turbidity very quickly. Some most common example is 2-methyl-2-butanol and 2-methyl propane-2-ol

Ques. Propanone on reaction with alkyl magnesium bromide followed by hydrolysis will produce

Ans. Tertiary alcohol, as we know when ketones are treated with Grignard reagents followed by hydrolysis will always yield tertiary alcohol or 3-degree alcohol

Ques. Picric acid is a yellow coloured compound. What is its chemical name?
Ans. Picric acid is 2,4,6-trinitrophenol

Picric acid is a yellow compound that is obtained by the nitration of phenol. it Is used as a dye and in the manufacture of explosives.

Ques. The best reagent to convert pent-3-en-2-vol into pent-3-en- 2-one is?

Ans. The best reagent to convert pent-3-en-2-vol into 3-en-3-one is chromic anhydride in glacial acetic acid. The reaction of conversion is an oxidation reaction. Here alcohol is oxidised to form ketones without affecting the unsaturated bond.

Ques. out of 2-chloroethane and ethanol which is more acidic and why?

Ans. The acidity of 2-chloroethyl Is higher than that of ethanol. The electron density of the Cl atom in H reduces due to the -I effect, as a result, O-H bond of 2 chlooroethanol weakens compared to the O-H bond of ethanol. hence 2-chloroetanol is more acidic than ethanol.

Ques. How are peroxides removed from ethers?

Ans. Peroxides can be easily removed from ethers while shaking well with FeSO₄ Solution.

Ques. What is Lucas’s test?

Ans. Lucas test is used to distinguish between primary, secondary and tertiary alcohols. Alcohol produce turbidity based on their reactiveness. Tertiary alcohol produces fastest while secondary alcohol after some time and primary not at all produce turbidity.

Ques. Arrange the following compound in the increasing order of acid strength?

p-cresol, p =-nitrophenol , phenol

Ans. p-cresol < phenol < p-nitrophenol is the increasing order of acid strength.

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Long Answers Type Questions ( 3 Marks Questions)

Ques. Give the IUPAC name of the following (All India 2009)

Ans. The IUPAC name of the compound Is assigned as per the naming rules;

1. Find the longest continuous carbon chain.
2. Identify the name of the group attached to this chain.
3. Name the chain consecutively.
4. Assemble the name, listing them in alphabetical order.
5. Add the prefixes di, tri as required.

IUPAC name: Hex-1-en-2-ol or 3-Hexenol

Ques. Draw the structure of 2, 6-Dimethylphenol. (All India 2011)

Ans. The structure of 2,6-Dimethylphenol is as follows;

Ques. Draw the structural formula of the 2-methyl propane- 2-ol molecule. (Delhi 2012)

Ans.

1. CH₂= CH – CH(OH) – CH₂– CH₂– CH₃

Ques. The C-O bond is much shorter in phenol than in ethanol. Give reason. (Comput. Delhi 2012)

Ans. The C-O bond of the phenol is sp3, hance is acquired a partial double bond but in ethanol, it is sp3 hybridize which is a single bond, also C-O bond in phenol has resonance effect due to which C-O bond is much shorter in phenol than in ethanol. Also in phenol, there is long pair of oxygen in conjunction with pie electron due to which the C-O acquired a partial double bond character.

Ques. List down a chemical test to distinguish between 2-Pentanol and 3-Pentanol.

Ans. 

2-pentanol when oxidized gives methylketone and this compound has a CH₃C=O group attached. Therefore when the iodoform test is done with CHI₃ and alkali on warming, a yellow ppt crystalline substance is formed.

And 3-pentanol does not show this test.

Ques. Explain; how to obtain acetophenone from phenol?

Ans. The chemical reaction for obtaining acetophenone is as follows

Ques. Write the IUPAC name of the following

Ans. by the rule of IUPAC naming ;

1. Look for the longest carbon chain.
2. Identify the group attached to it.
3. Name the chain continuously
4. Assemble the name alphabetically.

The IUPAC name is 2~Bromo-3-methylbut -2-ene-l-ol

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

Ans. o-nitrophenol forms an intramolecular H bond and p-nitrophenol gets associated with the intramolecular H bond, during the boiling process the strong H intramolecular bond increases the boiling point but the intramolecular H bonding cannot do so, hence O-Nitrophenol is more volatile than P-Nitrophenol.

Ques. What is the result when phenol is oxidized by Na₂Cr₂O₇/H₂SO₄?

Ans. Phenol forms benzoquinone on oxidation with Na₂Cr₂O₇/ H₂SO₄, in the presence of air, phenol slowly oxidized to a dark coloured mixture containing quinones.

Ques. Write the equation of the nitration of anisole

Ans. When anisole is nitrated with a mixture of concentrated HNO₃ and H₂SO₄, gives a mixture of ortho-Nitroanisole and para Nitroanisole as major products.

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Very Long Answer Questions ( 5 Marks Questions)

Ques. What is denatured alcohol?

Ans. Denatured alcohol is ethanol (ethyl alcohol) deliberately made unfit for human consumption by adding poisonous chemicals. Denatured alcohol is used as a solvent and as a fuel for alcohol burners and stoves. Denatured alcohol is ethanol unfit for humans. It is mainly used in the cosmetic industry and pharmaceuticals. when it is diluted, it can be used as a cleaner for glass and remove stains such as inks etc. Thinners also have some quantity of ethanol. in thinners, it works as a viscosity agent. Denatured alcohol is commonly legally available in three forms depending on the concentration of alcohol: industrial denatured alcohol (IDA) (wood naphtha is added); completely denatured alcohol (CDA) (isopropyl alcohol, methyl ethyl ketone and denatonium benzoate are added); and trade-specific denatured alcohol (TSDA).

Ques. What happens when benzene diazonium chloride is heated with water?

Ans. When Benzene Diazonium chloride is heated with water phenol, is formed along with the formation of nitrogen gas and hydrochloric acid as the by-products. The reaction is given as follows.

This process is frequently used to produce phenol from the analine. Diazonium salt is generated when online is treated with NaNO₂/HCL

Ques. Illustrate the following name reactions;

• Reimer-Tiemann reaction
• Williamson synthesis

Ans. I) Reimer-Tiemann Reaction – When phenol is treated with CHCl₃ in presence of aqueous NaOH at 340 K followed by hydrolysis of the same it gives salicylaldehydes

II) Williamson’s Synthesis: This reaction mainly involves the nucleophilic substitutions of the halide ion from the alkyl halide by the alkoxide ion by the SN₂

The reaction is explained below-

Ques.How would you obtain the following :

• Acetophenone from phenol
• 2-Methylpentan-2-ol from 2-methyl-1-pentane
• How is toluene obtained from phenol?

Ans. (i) Acetone from phenol is obtained from the following chemical reactions

(ii) The following chemical reaction is done to obtain the desired compound

(iii) Toluene is obtained from phenol with the help of the following process

Ques. Why is phenol more acidic than ethanol?

Ans. phenols are more acidic than alcohols because phenoxide ions are more stable than ethoxide ions. phenols as compared to alcohols can be explained based on resonance. (Resonance is a way of describing delocalized electron within certain molecules or polyatomic ions where the bond cannot be expressed with the help of the lewis formula) . Phenol based on resonance can be expressed by the following structure

The three structure of Phenol has a positive charge on the oxygen of the -OH group. This oxygen attracts the electron pairs of the O-H bond strongly towards itself, which weakens their bond and therefore facilitates the release of w. the phenoxide ion in resonance is stabilized as the following

We observe that both phenol and phenoxide ions are stabilised by resonance.

Now if we observe the structure the phenoxide ion is more stabilized than phenol. In phenol three contributing structures have both positive and negative charges, therefore, these nuclei are unstable. On the other hand, there is no structure for the phenoxide ion which requires separation thus, the resonance hybrid of phenol is less than phenoxide ion and the reaction is very much in favour of the phenoxide ion. Therefore the phenol is more acidic.

On the other hand, the case with alcohols is a bit different neither alcohol nor the alkoxide ion is stabilised by resonance.

Thus, phenols are more acidic than alcohol.

Ques. Explain the following

• Protonation of phenols Is difficult whereas ethanol easily undergoes protonation
• The boiling point of ethanol is higher than that of dimethyl ether.

Ans. (i) In phenols, a partial positive charge is acquired by the oxygen and therefore it is not easily protonated. On the other hand in ethanol, the alkyl group is an electron-releasing group and increases the electron density on 0 atoms. Therefore ethanol is easily protonated.

(ii) The molecule of ethanol are held together by intermolecular hydrogen bonding while dimethyl molecules have a weaker van der walls force of attraction between themselves. Since the hydrogen has string van der walls force of attraction, hence ethanol has a higher boiling point than dimethyl ether.

Ques. Solve the following

• Explain Friedel-craft reaction
• Show the nitration of anisole
• Explain the bromination of ethanoic acid medium

Ans. (i) In friedal craft reaction the acetylation pf anisole takes place, the reaction is explained below.

(ii) Show the nitration of anisole

(iii) Explain the bromination of ethanoic acid medium.

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