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All questions of Alcohols, Phenols and Ethers for NEET Exam

 Fermentation of Glucose to alcohol undergoes in presence of :
  • a)
    ZnO
  • b)
    Cr2O3
  • c)
    Invertase
  • d)
    Zymase
Correct answer is option 'D'. Can you explain this answer?

Lavanya Menon answered
The correct answer is option D
Zymase is an enzyme complex that catalyzes the fermentation of sugar into ethanol and carbon dioxide. It occurs naturally in yeasts. Zymase activity varies among yeast strains. Zymase is also the brand name of the drug pancrelipase.

C2H5OH and CH3OCH3 are:
  • a)
    Position isomers
  • b)
    Functional isomers
  • c)
    Chain isomer
  • d)
    Metamers
Correct answer is option 'B'. Can you explain this answer?

Vivek Rana answered
Alkyl alcohol and ether having same molecular formula ( Here C2H6O) are functional isomers of each other. As both having different functional group first one has -OH & second one has -O- functional group in the same carbon chain respectively .

Which alkene is obtained on dehydration of the following alcohol in the presence of H2SO4 ?
  • a)
  • b)
  • c)
  • d)
      None of the above
Correct answer is option 'B'. Can you explain this answer?

Mohit Rajpoot answered
 
Carbonium ion formed in 1st step undergoes rearrangement to give tert. carbonium ion since tert-carbonium ions are more stable than secondary one.

 Phenol is acidic due to resonance stabilization of its conjugate base :
  • a)
    O-H
  • b)
    Benzyl alcohol
  • c)
    Alkoxide ion
  • d)
    Phenoxide ion
Correct answer is option 'D'. Can you explain this answer?

Rishika Patel answered
Polarity of Phenol

Phenol, also known as benzenol or carbolic acid, is an aromatic compound that consists of a benzene ring bonded to a hydroxyl group (-OH). The presence of the hydroxyl group makes phenol a polar molecule because oxygen is more electronegative than carbon and hydrogen.

Acidity of Phenol

Phenol is considered an acid because it can donate a proton (H+) and form a conjugate base. The acidity of phenol is attributed to resonance stabilization of its conjugate base, the phenoxide ion.

Resonance Stabilization of Phenoxide Ion

When phenol loses a proton, it forms the phenoxide ion (C6H5O-). The phenoxide ion is resonance stabilized, which means that the negative charge can be delocalized over the entire ring system through resonance structures.

Resonance Structures of Phenoxide Ion

The resonance structures of the phenoxide ion can be represented as follows:

1. In the first resonance structure, the lone pair on the oxygen atom forms a double bond with carbon, while the negative charge is located on the oxygen atom.

2. In the second resonance structure, the lone pair on the oxygen atom forms a double bond with one of the carbon atoms in the ring, while the negative charge is located on that carbon atom.

3. In the third resonance structure, the lone pair on the oxygen atom forms a double bond with another carbon atom in the ring, while the negative charge is located on that carbon atom.

The resonance structures demonstrate that the negative charge of the phenoxide ion is delocalized over the entire ring system, resulting in stability.

Comparison with Other Options

a) O-H: The O-H bond in phenol is the source of acidity, but it does not explain the resonance stabilization of the conjugate base.

b) Benzyl alcohol: While benzyl alcohol also has an -OH group, it lacks the aromatic ring required for resonance stabilization of the conjugate base.

c) Alkoxide ion: Alkoxide ions are formed when an alcohol loses a proton, but they do not have the same resonance stabilization as the phenoxide ion.

Conclusion

The correct answer is option 'D' (Phenoxide ion) because the resonance stabilization of the phenoxide ion is responsible for the acidity of phenol. The delocalization of the negative charge over the aromatic ring system increases the stability of the conjugate base, making phenol acidic.

 When aryl halide is heated with 6-8% NaOH solution ,at 623 K under 300 atm pressure we get:
  • a)
    Phenol
  • b)
    Benzyl ether
  • c)
    Ethyl alcohol
  • d)
    Cumene
Correct answer is option 'A'. Can you explain this answer?

Divey Sethi answered
The correct answer is Option A.
 
The aryl halide is heated with 6-8%. NaOH solution at 623K under 300 atm pressure 1) it gives sodium phenoxide 2) sodium phenoxide treated with HCl(acidification) then it gives phenol.

 Nitration of anisole gives majorly:
  • a)
    Nitroanisole
  • b)
    para-Nitroanisole
  • c)
    ortho-Nitroanisole
  • d)
    meta-Nitroanisole
Correct answer is option 'B'. Can you explain this answer?

When anisole is nitrated with a mixture of conc HNO3 and H2SO4 it gives a mixture of ortho-Nitroanisole and para-Nitroanisole (major) products.

 Identify the alcohol or phenol having a stronger acidic nature from the following.
  • a)
    CH3CH2OH
  • b)
    C6H5OH
  • c)
    CH3CHOHCH2CH3
  • d)
    CH3CH2CH2CH2OH
Correct answer is option 'B'. Can you explain this answer?

Mohit Rajpoot answered
- Phenol (C₆H₅OH) is more acidic than typical alcohols.
- This is due to the resonance stabilization of the phenoxide ion formed when phenol loses a hydrogen ion (H⁺).
- The negative charge on the oxygen atom in phenoxide ion is delocalized over the aromatic ring, increasing stability and acidity.
- In contrast, alcohols like ethanol (CH₃CH₂OH) do not have such resonance stabilization, making them less acidic.
- Therefore, phenol is the strongest acid among the given options.

Which of the following statement is correct?
  • a)
    The -OH group in phenol is meta directing.
  • b)
    The electron releasing groups increase the acidic character of phenols.
  • c)
    Phenols are less acidic than aromatic alcohols.
  • d)
    Boiling point of phenol is higher than that of toluene of comparable molecular mass.
Correct answer is option 'D'. Can you explain this answer?

Divey Sethi answered
The correct answer is Option D.
Phenols have higher boiling point than toluene due to the presence of intermolecular hydrogen bonding in phenols. The formation of hydrogen bonds increases the intermolecular force of attraction between the phenol molecules and thereby increases its boiling point.

Can you explain the answer of this question below:

The acidity of phenols is due to

  • A:

    Oxidation process

  • B:

    Resonance stabilization of its ions.

  • C:

    Hybridisation

  • D:

    Presence of O-H group

The answer is b.

Rahul Bansal answered
The acidity of phenols is due to its ability to lose hydrogen ion to form phenoxide ions. In a phenol molecule, the sp2hybridised carbon atom of benzene ring attached directly to the hydroxyl group acts as an electron withdrawing group. This sp2 hybridized carbon atom of benzene ring attached directly to the hydroxyl group has higher electronegativity in comparison to hydroxyl group. Due to the higher electronegativity of this carbon atom in comparison to the hydroxyl group attached, electron density decreases on oxygen atom. The decrease in electron density increases the polarity of O-H bond and results in the increase in ionization of phenols. Thus, the phenoxide ion is formed. The phenoxide ion formed is stabilized by the delocalization of negative charge due to the resonance in benzene ring. Phenoxide ion has greater stability than phenols, as in case of phenol charge separation takes place during resonance.The resonance structures of phenoxide ions explain the delocalization of negative charge. In case of substituted phenols, acidity of phenols increases in the presence of electron withdrawing group. This is due to the stability of the phenoxide ion generated. The acidity of phenols further increases if these groups are attached at ortho and para positions. This is due to the fact that the negative charge in phenoxide ion is mainly delocalized at ortho and para positions of the attached benzene ring. On the other hand, the acidity of phenols decreases in presence of electron donating groups as they prohibit the formation of phenoxide ion.

 We can obtain picric acid from phenol by:
  • a)
    Sulphonation of phenol
  • b)
    By Reimer Tiemann reaction
  • c)
    Nitration of phenol
  • d)
    Halogenation of phenol
Correct answer is option 'C'. Can you explain this answer?

Shreya Gupta answered
Phenol heated with sulphuric acid gives phenol disulphonic acid, which further on reaction with nitric acid forms picric acid (2,4,6-trinitrophenol).

IUPAC name of m-cresol is ___________.
  • a)
    3-methylphenol
  • b)
    3-chlorophenol
  • c)
     3-methoxyphenol
  • d)
    benzene-1,3-diol
Correct answer is option 'A'. Can you explain this answer?

Preeti Iyer answered
Meta-Cresol, also 3-methylphenol, is an organic compound with the formula CH3C6H4(OH). It is a colourless, viscous liquid that is used as an intermediate in the production of other chemicals. It is a derivative of phenol and is an isomer of p-cresol and o-cresol.

Which catalyst is used in Fischer-Speier esterification?
  • a)
    Concentrated H2SO4   
  • b)
    Dry HCl gas
  • c)
    Concentrated HNO3
  • d)
    Pyridine
Correct answer is option 'A'. Can you explain this answer?

Pooja Mehta answered
Esterification is a relatively slow process at room temperature and does not proceed to completion. Concentrated sulfuric acid is used as a catalyst, and has a dual role: Speeds up the reaction. Acts as a dehydrating agent, forcing the equilibrium to the right and resulting in a greater yield of ester.

 Williamsons synthesis is an example of :
  • a)
    Electrophilic substitution
  • b)
    Electrophilic addition
  • c)
    Nucleophilic substitution reaction
  • d)
    Nucleophilic addition
Correct answer is option 'C'. Can you explain this answer?

Shreya Gupta answered
The Williamson ether synthesis is an organic reaction used to convert an alcohol and an alkyl halide to an ether using a base such as NaOH. The mechanism begins with the base abstracting the proton from the alcohol to form an alkoxide intermediate. The alkoxide then attacks the alkyl halide in a nucleophilic substi-tution reaction (SN2), which results in the formation of the final ether product and a metal halide by-product.


Phenol can be distinguished from ethanol by the reactions with _________.
  • a)
    Br2/water
  • b)
    Na
  • c)
    Neutral FeCl3
  • d)
    A and C
Correct answer is option 'D'. Can you explain this answer?

Nisha Banerjee answered
  • Phenol can be distinguished from ethanol using Br2/water and Neutral FeCl3.
  • Br2/water: Phenol reacts with bromine water to give a white precipitate of 2,4,6-tribromophenol, while ethanol does not react.
  • Neutral FeCl3: Phenol forms a violet complex with neutral ferric chloride, whereas ethanol shows no color change.
  • Therefore, options A and C are correct for distinguishing phenol from ethanol.

Ethers may be used as solvents because they react only with which of the following reactants?
  • a)
    Acids
  • b)
    Bases
  • c)
    Oxidising agent
  • d)
    Reducing agents
Correct answer is option 'A'. Can you explain this answer?

Geetika Shah answered
Ethers resist the attack of nucleophiles and bases. However, they are very good solvents in many organic reactions due to their ability to solvate cations by donating the electron pair from oxygen atom. Ethers are generally less reactive and react only with acids.

Isopropyl alcohol on oxidation forms:
  • a)
    Acetone
  • b)
    Ether
  • c)
    Acetaldehyde
  • d)
    Methane
Correct answer is option 'A'. Can you explain this answer?

Rahul Bansal answered
The oxidation of isopropyl alcohol by potassium dichromate (K 2Cr 2O 7) gives acetone, the simplest ketone: Unlike aldehydes, ketones are relatively resistant to further oxidation, so no special precautions are required to isolate them as they form.

Which of the following compounds will react with sodium hydroxide solution in water?
  • a)
    C6H5OH
  • b)
    C6H5CH2OH
  • c)
    (CH3)3COH
  • d)
    C2H5OH
Correct answer is option 'A'. Can you explain this answer?

Vijay Bansal answered
When phenol reacts with sodium hydroxide solution it gives a colourless solution containing sodium phenoxide.

In this reaction, the hydrogen ion has been removed by the strongly basic hydroxide ion in the sodium hydroxide solution.

An organic compound X is oxidised by using acidified K2Cr2O7. The product obtained reacts with Phenyl hydrazine but does not answer silver mirror test. The possible structure of X is
  • a)
    CH3CH2OH
  • b)
    CH3CHO
  • c)
    (CH3)2CHOH 
  • d)
    None of the these
Correct answer is option 'C'. Can you explain this answer?

Baby Ghosh answered
Yup...it will be propan-2-ol..by oxidation it..it will convert into acetone and it reacts with phenyl hydrazine,it produces acetone phenyl hydrazone and there is no aldehyde grp in acetone. so it doesn't react in silver mirror test means with tollen's reagent..

Which reaction(s) given below gives dicarbonyl?
  • a)
  • b)
  • c)
  • d)
Correct answer is option 'A,D'. Can you explain this answer?

Gunjan Lakhani answered
Syn vicinal diols undergo oxidative cleavage with HIO4 giving diols, Option (b) and option (c) are anti diol and have restricted rotation.

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