Alcohols, Phenols, and Ethers - Class 12 Chemistry
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Questions and Answers

What is the IUPAC name of glycerol and its structural formula?

The IUPAC name of glycerol is propan-1,2,3-triol. Its structural formula is a three-carbon chain with hydroxyl groups on each carbon.

What is the IUPAC name for the compound 3-ethyl-5-methylhexane-2,4-diol?

The IUPAC name for the compound is 3-ethyl-5-methylhexane-2,4-diol.

Explain the factors affecting the solubility of alcohols in water.

The solubility of alcohols in water is influenced mainly by the presence of hydroxyl groups, which facilitate hydrogen bonding, and the hydrophobic hydrocarbon chain.

What is denatured alcohol and how is it made?

<p>Denatured alcohol is ethanol made unfit for human consumption by adding chemicals like methanol. This process typically involves adding at least 5% methanol to ethanol.</p> Signup and view all the answers

Suggest a reagent to oxidize a secondary alcohol to a ketone.

<p>Chromic acid (CrO3) or pyridinium chlorochromate can be used to oxidize a secondary alcohol to a ketone.</p> Signup and view all the answers

Which is more acidic, 2-chloroethanol or ethanol, and why?

<p>2-chloroethanol is more acidic than ethanol because the chlorine atom withdraws electron density from the O-H bond, weakening it.</p> Signup and view all the answers

What is the IUPAC name of 3-methylpent-2-ene-1,2-diol?

<p>The IUPAC name of the compound is 3-methylpent-2-ene-1,2-diol.</p> Signup and view all the answers

Describe the reaction of a secondary alcohol upon oxidation.

<p>A secondary alcohol, when oxidized, typically converts to a ketone without affecting any adjacent double bonds.</p> Signup and view all the answers

What reagent is suggested for the conversion of ethanol to ethanal?

<p>Pyridinium chlorochromate is suggested for the conversion.</p> Signup and view all the answers

Which compounds are used to convert ethanol into ethanoic acid?

<p>Ethanol can be converted into ethanoic acid using acidified KMnO4 or K2Cr2O7.</p> Signup and view all the answers

Explain why o-nitrophenol is more volatile than p-nitrophenol.

<p>O-nitrophenol is more volatile due to intramolecular hydrogen bonding, while p-nitrophenol has intermolecular hydrogen bonding.</p> Signup and view all the answers

Which is more acidic, o-nitrophenol or o-cresol, and why?

<p>O-nitrophenol is more acidic than o-cresol due to the electron-withdrawing effect of the nitro group stabilizing the phenoxide ion.</p> Signup and view all the answers

What compound precipitates when phenol is treated with bromine water?

<p>A white precipitate of 2,4,6-tribromophenol is formed.</p> Signup and view all the answers

Arrange phenol, o-nitrophenol, and o-cresol in increasing order of acidity.

<p>Increasing order of acidity is: o-cresol &lt; phenol &lt; o-nitrophenol.</p> Signup and view all the answers

What is the decreasing order of reactivity of sodium metal towards primary, secondary, and tertiary alcohols?

<p>The order of reactivity is: primary &gt; secondary &gt; tertiary alcohols.</p> Signup and view all the answers

What are the products formed when benzene diazonium chloride is heated with water?

<p>Phenol, nitrogen gas, and hydrochloric acid are formed.</p> Signup and view all the answers

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

<p>Propan-2-one can be treated with Grignard reagents to give tert-butyl alcohol.</p> Signup and view all the answers

List the alcohol isomers with the molecular formula C4H10O and state which exhibits optical activity.

<p>The isomers are butan-1-ol, butan-2-ol, tert-butanol, and isobutanol. Butan-2-ol exhibits optical activity.</p> Signup and view all the answers

Why is the OH group in phenols more strongly held compared to that in alcohols?

<p>The OH group in phenols is more strongly held due to its direct attachment to sp2 hybridized carbon, granting partial double bond character.</p> Signup and view all the answers

Why are nucleophilic substitution reactions uncommon in phenols?

<p>Nucleophilic substitution is uncommon in phenols due to the high electron density on the benzene ring repelling nucleophiles.</p> Signup and view all the answers

What is the mechanism involved in the preparation of alcohols from alkenes?

<p>Alcohols are prepared from alkenes through direct hydration or indirect hydration involving sulfuric acid.</p> Signup and view all the answers

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

<p>O=C=O is nonpolar because its C=O dipoles cancel each other, while R-O-R is polar due to the asymmetry and presence of dipole moments.</p> Signup and view all the answers

What factor affects the reactivity of alcohols with Lucas reagent?

<p>The stability of carbocations affects reactivity, with tertiary carbocations being the most stable and reactive, followed by secondary and primary.</p> Signup and view all the answers

Describe the first step in converting phenol to aspirin.

<p>The first step is creating a phenoxide ion by treating phenol with NaOH.</p> Signup and view all the answers

Why is phenol more easily nitrated than benzene?

<p>The -OH group in phenol increases electron density at the ortho and para positions, making it more reactive than benzene.</p> Signup and view all the answers

Why is phenoxide ion used instead of phenol in Kolbe's reaction?

<p>Phenoxide ion is more reactive than phenol in electrophilic aromatic substitution, which is essential for reacting with carbon dioxide.</p> Signup and view all the answers

Explain why the dipole moment of phenol is smaller than that of methanol.

<p>The carbon in phenol is sp2 hybridized, causing a less polar C-O bond compared to the sp3 hybridized carbon in methanol.</p> Signup and view all the answers

Why can't di-tert-butyl ether be prepared using Williamson synthesis?

<p>The reaction of tert-butyl bromide with sodium tert-butoxide leads to elimination instead of substitution.</p> Signup and view all the answers

What explains the lower bond angle in alcohols compared to the tetrahedral angle?

<p>In alcohols, two lone pairs of electrons on oxygen cause increased repulsion, resulting in a smaller bond angle.</p> Signup and view all the answers

How do molecular mass and hydrogen bonding impact the solubility of alcohols in water?

<p>Lower molecular mass alcohols have smaller hydrocarbon parts, allowing them to form more hydrogen bonds with water and increasing solubility.</p> Signup and view all the answers

What role does the nitro group play in the acidity of p-nitrophenol compared to phenol?

<p>The nitro group withdraws electron density from the O-H bond in p-nitrophenol, making it more acidic than phenol.</p> Signup and view all the answers

Why do alcohols and ethers show different boiling points even if they have comparable molecular masses?

<p>Alcohols can form strong hydrogen bonds, while ethers cannot, leading to higher boiling points for alcohols.</p> Signup and view all the answers

What makes the C-O bond in phenol stronger than in methanol?

<p>In phenol, the resonance with the aromatic ring confers partial double bond character to the C–O bond, making it stronger.</p> Signup and view all the answers

What is the significance of carbocation stability in the reactivity of alcohols?

<p>Carbocation stability dictates the reactivity of alcohols, with more stable carbocations leading to higher reactivity.</p> Signup and view all the answers

How does the hybridization of carbon atoms affect dipole moments in alcohols compared to ethers?

<p>The sp2 hybridization in phenolic compounds leads to different electronic effects compared to sp3 in alcohols, affecting dipole moments.</p> Signup and view all the answers

In what way does the presence of bulky R groups influence the C-O-C bond angle in ethers?

<p>The presence of bulky R groups increases the bond angle in ethers, causing it to be slightly greater than the tetrahedral angle.</p> Signup and view all the answers

What is the relationship between sp2 hybridization and the stability of the C-O bond in phenol compared to methanol?

<p>The C-O bond in phenol, which is sp2 hybridized, is more stable than that in methanol due to the partial double bond character from resonance.</p> Signup and view all the answers

Arrange water, ethanol, and phenol in increasing order of acidity and explain your reasoning.

<p>The order is ethanol &lt; water &lt; phenol because phenol is resonance stabilized after losing a proton, while ethanol has an electron-releasing ethyl group that destabilizes its conjugate base.</p> Signup and view all the answers

What is the starting material used in the industrial preparation of phenol?

<p>The starting material is cumene.</p> Signup and view all the answers

Why is a Lewis acid not required for the bromination of phenol?

<p>A Lewis acid is not needed because the oxygen atom in phenol polarizes Br2 to create the reactive electrophile Br+ without external assistance.</p> Signup and view all the answers

Describe the mechanism by which phenol can be converted to aspirin.

<p>Phenol is converted to aspirin by first forming sodium salicylate through carbon dioxide absorption and heating, then acetylating salicylic acid with acetic anhydride.</p> Signup and view all the answers

What role do biocatalysts play in the industrial production of ethanol?

<p>Biocatalysts, specifically enzymes from yeast, facilitate the fermentation of sugars in molasses to produce ethanol.</p> Signup and view all the answers

What is the significance of the proton shift in the conversion of sodium phenoxide to salicylic acid?

<p>The proton shift is crucial as it allows the formation of an unstable intermediate, which later becomes sodium salicylate before being acidified to salicylic acid.</p> Signup and view all the answers

Why does the ethyl group in ethanol make it a weaker acid compared to phenol?

<p>The ethyl group in ethanol increases the electron density on the O-H bond, making it harder for the proton to be released compared to phenol.</p> Signup and view all the answers

Explain how the C6H5-O bond in anisole is affected when a proton is added during the reaction with HI.

<p>Protonation of anisole forms a methyl phenyl oxonium ion, weakening the C-O bond (O-CH3) compared to the stable partial double bond character of O-C6H5.</p> Signup and view all the answers

What happens when bromine water is used on phenol?

<p>Bromine water replaces all hydrogen atoms at the ortho and para positions of phenol with bromine due to the activation by phenoxide ions.</p> Signup and view all the answers

Study Notes

Alcohols, Phenols, and Ethers - Class 12 Chemistry

  • Glycerol: Trihydric alcohol; IUPAC name: propan-1,2,3-triol. Structure shown in provided text.

IUPAC Nomenclature

  • Example IUPAC names for compounds provided.
    • 3-ethyl-5-methylhexane-2,4-diol
    • 1-methoxy-3-nitrocyclohexane
    • 3-methylpent-2-ene-1,2-diol

Solubility of Alcohols in Water

  • Lower molecular weight alcohols are soluble in water due to hydrogen bonding with water molecules.

Denatured Alcohol

  • Denatured alcohol is ethanol made unfit for human consumption by adding other chemicals. This process of denaturing doesn't alter the chemical structure but makes it unsuitable for drinking. Methanol is often used in denaturing solutions for fuels and solvents.

Alcohol Reactions - Reagents

  • Primary alcohol to ketone/aldehyde: CrO₃ or pyridinium chlorochromate.
  • Ethanol to ethanal: Pyridinium chlorochromate.
  • Ethanol to ethanoic acid: Acidified KMnO₄ or K₂Cr₂O₇ (powerful oxidizers).

Acidity of Alcohols and Phenols

  • 2-chloroethanol vs. ethanol: 2-chloroethanol is more acidic due to the electron-withdrawing chlorine atom (-I effect) that weakens the O-H bond.
  • o-nitrophenol vs. p-nitrophenol: o-nitrophenol is more volatile due to intramolecular hydrogen bonding, while p-nitrophenol has intermolecular hydrogen bonding.
  • o-nitrophenol vs. o-cresol: o-nitrophenol is more acidic due to the electron-withdrawing nitro group (−NO₂), which stabilizes the phenoxide ion. O-cresol is less acidic due to the electron-releasing methyl group (−CH₃).
  • Increasing acidity: o-cresol < phenol < o-nitrophenol (given specific examples)

Reactions of Phenol

  • Bromination: Bromination of phenol produces 2,4,6-tribromophenol (white precipitate).
  • Mechanism: The reaction proceeds by electrophilic substitution, but the hydroxyl group on phenol activates the ring more effectively in this case (important concept for the reaction).

Alcohols and Sodium Metal

  • Reactivity Decreasing order for reacting with sodium metal is primary > secondary > tertiary alcohols. The +I effect increases the electron density on oxygen which makes the O-H bond weaker and thus reactivity decreases.

Benzene Diazonium Chloride

  • Heated with water to form phenol as well as nitrogen gas and hydrochloric acid.

Acidity Comparison

  • Acidity order: H₂O > ROH > HC≡CH (water > alcohol > acetylene, Water being the strongest acid among the others cited)

Ethanol Production by Fermentation

  • Enzymes: Invertase and zymase are used in industrial fermentation.
  • Reactions: Sucrose is converted into glucose and fructose, then further into ethanol and CO₂.

Conversion of Propan-2-one to tert-butyl alcohol

  • Propan-2-one (a ketone) can be converted into tert-butyl alcohol using Grignard reagents.

C₄H₁₀O Isomers

  • Four isomers of C₄H₁₀O exist, as given. Some exhibit optical activity.

Bond Strength in Phenols and Alcohols

  • Phenol's O-H bond is stronger than in alcohols due to resonance with benzene ring. The conjugated nature of the structure makes the C-O bond in phenol have some double bond character

Nucleophilic Substitution in Phenols

  • Nucleophilic substitution reactions are uncommon due to the high electron density on the benzene ring, discouraging approach by the nucleophile

Alcohol Preparation from Alkenes

  • Alcohols are prepared from alkenes through hydration (direct or indirect) mechanisms in the presence of catalysts.

Dipole Moments

  • O=C=O (Carbon dioxide): Nonpolar due to cancellation of opposing dipole moments.

  • ROR (Ether): Polar due to the unequal sharing of electrons.

Reactivity of Alcohols with Lucas Reagent

  • Reactivity order with Lucas reagent: Tertiary > Secondary > Primary. This is due to the stability of the carbocation formed during SN1 reactions

Converting Phenol to Aspirin

  • Phenol can be converted to aspirin via a multi-step process. This process uses alkali, base, carbon dioxide (and pressure), then acetylation to obtain the final product of aspirin.

Industrial Preparation via Biocatalysts (Ethanol)

  • Enzymes (biocatalysts) are used in converting molasses to ethanol. Fermentation is the method of accomplishing this.

Nitration of Benzene and Phenol

  • Phenol is more easily nitrated than benzene because the hydroxyl group increases electron density at the ortho and para positions, activating the ring towards electrophilic substitution.


Williamson Ether Synthesis

  • Williamson synthesis is not feasible for di-tert-butyl ether due to elimination competing with the desired substitution reaction when using strong bases.


Bond Angles in Alcohols and Ethers

  • C-O-H bond angle in alcohol is slightly less than tetrahedral due to lone pair repulsions.

  • C-O-C bond angle in ethers is slightly greater than tetrahedral due to repulsions from larger alkyl groups.

Solubility in Water and Boiling Points

  • Low molecular weight alcohols are soluble in water due to extensive hydrogen bonding.

  • Alcohols and ethers of comparable molar mass have vastly different boiling points due to hydrogen bonding in alcohols and no hydrogen bonding in ethers.

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Test your knowledge on the properties and reactions of alcohols, phenols, and ethers with this quiz designed for Class 12 Chemistry. Topics include IUPAC nomenclature, solubility in water, and denatured alcohol. Understand the key concepts and reactions involving these important organic compounds.

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