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Q7.29:
Explain the fact that in aryl alkyl ethers (i) the alkoxy group activates the benzene ring towards electrophilic substitution and (ii) it directs the incoming substituents to ortho and para positions in benzene ring.
Solution :
Initial Theoretical Foundation: Resonance in Aryl Alkyl Ethers
In aryl alkyl ethers (represented by the general formula $Ar-O-R$, where $Ar$ is a phenyl group and $R$ is an alkyl group), the oxygen atom possesses two lone pairs of electrons. One of these lone pairs undergoes delocalization into the $\pi$-electron system of the benzene ring. This phenomenon is known as the $+M$ (mesomeric) or resonance effect.
Step 1: Analyzing Activation of the Benzene Ring
The $+M$ effect of the $-OR$ group increases the electron density within the aromatic ring. This enrichment of the $\pi$-electron cloud makes the benzene ring more nucleophilic, thereby increasing its reactivity towards electrophiles. Since electrophilic substitution reactions are governed by the ability of the ring to donate electrons to the incoming electrophile [$E^+$], the increased electron density directly enhances the reaction rate [Per Electrophilic Aromatic Substitution mechanism].
Step 2: Determining Orientation (Ortho/Para Direction)
To understand the directing influence, we must observe the canonical structures formed by the resonance interaction of the $-OR$ group with the benzene ring:
Upon analysis of the resonance contributors, the negative charge is delocalized onto the carbon atoms at the ortho and para positions relative to the alkoxy group. Mathematically and logically:
- The resonance structures indicate that the ortho and para positions have a partial negative charge.
- The electrophile [$E^+$], being electron-deficient, is naturally attracted to these regions of high electron density [Coulombic interaction principles].
- There is no significant increase in electron density at the meta position, explaining the lack of meta-substitution.
Summary of Analytical Results
| Effect | Mechanism | Chemical Consequence |
|---|---|---|
| Activation | $+M$ effect increases ring electron density | Facilitates Electrophilic Substitution |
| Orientation | Negative charge localization at $o-$ and $p-$ | Directs $E^+$ to $o-$ and $p-$ positions |
Final Solution: The alkoxy group activates the benzene ring due to the $+M$ effect, which donates electron density into the ring through resonance. It directs substituents to ortho and para positions because the canonical resonance structures show an increased electron density specifically at these positions, making them the most nucleophilic sites for electrophilic attack.
More Questions from Class 12 Chemistry Alcohols Exercises
- Q7.1: Write IUPAC names of the following compounds:
- Q7.1: Write IUPAC names of the following compounds:
- Q7.1: Write IUPAC names of the following compounds:
- Q7.1: Write IUPAC names of the following compounds:
- Q7.1: Write IUPAC names of the following compounds:
- Q7.1: Write IUPAC names of the following compounds:
- Q7.1: Write IUPAC names of the following compounds:
- Q7.1: Write IUPAC names of the following compounds:
- Q7.1: Write IUPAC names of the following compounds:
- Q7.1: Write IUPAC names of the following compounds:
- Q7.1 (x): Write IUPAC names of the following compounds: \(C_{6}H_{5}–O–C_{2}H_{5}\)
- Q7.1 (xi): Write IUPAC names of the following compounds: \(C_{6}H_{5}–O–C_{7}H_{15}(n–)\)
- Q7.1(i): Write IUPAC names of the following compounds:
- Q7.1(ii): Write IUPAC names of the following compounds:
- Q7.1(iii): Write IUPAC names of the following compounds:
- Q7.1(iv): Write IUPAC names of the following compounds:
- Q7.1(ix): Write IUPAC names of the following compounds:
- Q7.1(v): Write IUPAC names of the following compounds:
- Q7.1(vi): Write IUPAC names of the following compounds:
- Q7.1(vii): Write IUPAC names of the following compounds:
- Q7.1(viii): Write IUPAC names of the following compounds:
- Q7.1(x): Write IUPAC names of the following compounds:
- Q7.1(xi): Write IUPAC names of the following compounds:
- Q7.1(xii): Write IUPAC names of the following compounds:
- Q7.10: Write chemical reaction for the preparation of phenol from chlorobenzene.
- Q7.10: Write chemical reaction for the preparation of phenol from chlorobenzene.
- Q7.11: Write the mechanism of hydration of ethene to yield ethanol.
- Q7.11: Write the mechanism of hydration of ethene to yield ethanol.
- Q7.12: You are given benzene, conc. \(H_{2}SO_{4}\) and \(NaOH\). Write the equations for the preparation of phenol using these reagents.
- Q7.12: You are given benzene, conc. ((H_{2}SO_{4})) and NaOH. Write the equations for the preparation of phenol using these reagents.
- Q7.13 (i): Show how will you synthesise: 1-phenylethanol from a suitable alkene.
- Q7.13 (ii): Show how will you synthesise: cyclohexylmethanol using an alkyl halide by an \(S_{N}2\) reaction.
- Q7.13 (iii): Show how will you synthesise: pentan-1-ol using a suitable alkyl halide?
- Q7.13(i): Show how will you synthesise: 1-phenylethanol from a suitable alkene.
- Q7.13(ii): Show how will you synthesise: cyclohexylmethanol using an alkyl halide by an ((S_{N}2)) reaction.
- Q7.13(iii): Show how will you synthesise: pentan-1-ol using a suitable alkyl halide?
- Q7.14: Give two reactions that show the acidic nature of phenol. Compare acidity of phenol with that of ethanol.
- Q7.14: Give two reactions that show the acidic nature of phenol. Compare acidity of phenol with that of ethanol.
- Q7.15: Explain why is ortho nitrophenol more acidic than ortho methoxyphenol ?
- Q7.15: Explain why is ortho nitrophenol more acidic than ortho methoxyphenol ?
- Q7.16: Explain how does the \(–OH\) group attached to a carbon of benzene ring activate it towards electrophilic substitution?
- Q7.16: Explain how does the –OH group attached to a carbon of benzene ring activate it towards electrophilic substitution?
- Q7.17 (i): Give equations of the following reactions: Oxidation of propan-1-ol with alkaline \(KMnO_{4}\) solution.
- Q7.17 (ii): Give equations of the following reactions: Bromine in \(CS_{2}\) with phenol.
- Q7.17 (iii): Give equations of the following reactions: Dilute \(HNO_{3}\) with phenol.
- Q7.17 (iv): Give equations of the following reactions: Treating phenol wih chloroform in presence of aqueous \(NaOH\).
- Q7.17(i): Give equations of the following reactions: Oxidation of propan-1-ol with alkaline ((KMnO_{4})) solution.
- Q7.17(ii): Give equations of the following reactions: Bromine in ((CS_{2})) with phenol.
- Q7.17(iii): Give equations of the following reactions: Dilute ((HNO_{3})) with phenol.
- Q7.17(iv): Give equations of the following reactions: Treating phenol wih chloroform in presence of aqueous NaOH.
- Q7.18 (i): Explain the following with an example. Kolbe’s reaction.
- Q7.18 (ii): Explain the following with an example. Reimer-Tiemann reaction.
- Q7.18 (iii): Explain the following with an example. Williamson ether synthesis.
- Q7.18 (iv): Explain the following with an example. Unsymmetrical ether.
- Q7.18(i): Explain the following with an example. Kolbe’s reaction.
- Q7.18(ii): Explain the following with an example. Reimer-Tiemann reaction.
- Q7.18(iii): Explain the following with an example. Williamson ether synthesis.
- Q7.18(iv): Explain the following with an example. Unsymmetrical ether.
- Q7.19: Write the mechanism of acid dehydration of ethanol to yield ethene.
- Q7.19: Write the mechanism of acid dehydration of ethanol to yield ethene.
- Q7.2 (i): Write structures of the compounds whose IUPAC names are as follows: 2-Methylbutan-2-ol
- Q7.2 (ii): Write structures of the compounds whose IUPAC names are as follows: 1-Phenylpropan-2-ol
- Q7.2 (iii): Write structures of the compounds whose IUPAC names are as follows: 3,5-Dimethylhexane –1, 3, 5-triol
- Q7.2 (iv): Write structures of the compounds whose IUPAC names are as follows: 2,3 – Diethylphenol
- Q7.2 (ix): Write structures of the compounds whose IUPAC names are as follows: Cyclopent-3-en-1-ol
- Q7.2 (v): Write structures of the compounds whose IUPAC names are as follows: 1 – Ethoxypropane
- Q7.2 (vi): Write structures of the compounds whose IUPAC names are as follows: 2-Ethoxy-3-methylpentane
- Q7.2 (vii): Write structures of the compounds whose IUPAC names are as follows: Cyclohexylmethanol
- Q7.2 (viii): Write structures of the compounds whose IUPAC names are as follows: 3-Cyclohexylpentan-3-ol
- Q7.2 (x): Write structures of the compounds whose IUPAC names are as follows: 4-Chloro-3-ethylbutan-1-ol.
- Q7.2(i): Write structures of the compounds whose IUPAC names are as follows: 2-Methylbutan-2-ol
- Q7.2(ii): Write structures of the compounds whose IUPAC names are as follows: 1-Phenylpropan-2-ol
- Q7.2(iii): Write structures of the compounds whose IUPAC names are as follows: 3,5-Dimethylhexane –1, 3, 5-triol
- Q7.2(iv): Write structures of the compounds whose IUPAC names are as follows: 2,3 – Diethylphenol
- Q7.2(ix): Write structures of the compounds whose IUPAC names are as follows: Cyclopent-3-en-1-ol
- Q7.2(v): Write structures of the compounds whose IUPAC names are as follows: 1 – Ethoxypropane
- Q7.2(vi): Write structures of the compounds whose IUPAC names are as follows: 2-Ethoxy-3-methylpentane
- Q7.2(vii): Write structures of the compounds whose IUPAC names are as follows: Cyclohexylmethanol
- Q7.2(viii): Write structures of the compounds whose IUPAC names are as follows: 3-Cyclohexylpentan-3-ol
- Q7.2(x): Write structures of the compounds whose IUPAC names are as follows: 4-Chloro-3-ethylbutan-1-ol.
- Q7.20 (i): How are the following conversions carried out? Propene \(\rightarrow\) Propan-2-ol.
- Q7.20 (ii): How are the following conversions carried out? Benzyl chloride \(\rightarrow\) Benzyl alcohol.
- Q7.20 (iii): How are the following conversions carried out? Ethyl magnesium chloride \(\rightarrow\) Propan-1-ol.
- Q7.20 (iv): How are the following conversions carried out? Methyl magnesium bromide \(\rightarrow\) 2-Methylpropan-2-ol.
- Q7.20(i): How are the following conversions carried out? Propene ((\rightarrow)) Propan-2-ol.
- Q7.20(ii): How are the following conversions carried out? Benzyl chloride ((\rightarrow)) Benzyl alcohol.
- Q7.20(iii): How are the following conversions carried out? Ethyl magnesium chloride ((\rightarrow)) Propan-1-ol.
- Q7.20(iv): How are the following conversions carried out? Methyl magnesium bromide ((\rightarrow)) 2-Methylpropan-2-ol.
- Q7.21 (i): Name the reagents used in the following reactions: Oxidation of a primary alcohol to carboxylic acid.
- Q7.21 (ii): Name the reagents used in the following reactions: Oxidation of a primary alcohol to aldehyde.
- Q7.21 (iii): Name the reagents used in the following reactions: Bromination of phenol to 2,4,6-tribromophenol.
- Q7.21 (iv): Name the reagents used in the following reactions: Benzyl alcohol to benzoic acid.
- Q7.21 (v): Name the reagents used in the following reactions: Dehydration of propan-2-ol to propene.
- Q7.21 (vi): Name the reagents used in the following reactions: Butan-2-one to butan-2-ol.
- Q7.21(i): Name the reagents used in the following reactions: Oxidation of a primary alcohol to carboxylic acid.
- Q7.21(ii): Name the reagents used in the following reactions: Oxidation of a primary alcohol to aldehyde.
- Q7.21(iii): Name the reagents used in the following reactions: Bromination of phenol to 2,4,6-tribromophenol.
- Q7.21(iv): Name the reagents used in the following reactions: Benzyl alcohol to benzoic acid.
- Q7.21(v): Name the reagents used in the following reactions: Dehydration of propan-2-ol to propene.
- Q7.21(vi): Name the reagents used in the following reactions: Butan-2-one to butan-2-ol.
- Q7.22: Give reason for the higher boiling point of ethanol in comparison to methoxymethane.
- Q7.22: Give reason for the higher boiling point of ethanol in comparison to methoxymethane.
- Q7.23: Give IUPAC names of the following ethers:
- Q7.23: Give IUPAC names of the following ethers:
- Q7.23: Give IUPAC names of the following ethers:
- Q7.23: Give IUPAC names of the following ethers:
- Q7.23: Give IUPAC names of the following ethers:
- Q7.23(i): Give IUPAC names of the following ethers:
- Q7.23(ii): Give IUPAC names of the following ethers:
- Q7.23(iii): Give IUPAC names of the following ethers:
- Q7.23(iv): Give IUPAC names of the following ethers:
- Q7.23(v): Give IUPAC names of the following ethers:
- Q7.23(vi): Give IUPAC names of the following ethers:
- Q7.24 (i): Write the names of reagents and equations for the preparation of the following ethers by Williamson’s synthesis: 1-Propoxypropane
- Q7.24 (ii): Write the names of reagents and equations for the preparation of the following ethers by Williamson’s synthesis: Ethoxybenzene
- Q7.24 (iii): Write the names of reagents and equations for the preparation of the following ethers by Williamson’s synthesis: 2-Methoxy-2-methylpropane
- Q7.24 (iv): Write the names of reagents and equations for the preparation of the following ethers by Williamson’s synthesis: 1-Methoxyethane
- Q7.24(i): Write the names of reagents and equations for the preparation of the following ethers by Williamson’s synthesis: 1-Propoxypropane
- Q7.24(ii): Write the names of reagents and equations for the preparation of the following ethers by Williamson’s synthesis: Ethoxybenzene
- Q7.24(iii): Write the names of reagents and equations for the preparation of the following ethers by Williamson’s synthesis: 2-Methoxy-2-methylpropane
- Q7.24(iv): Write the names of reagents and equations for the preparation of the following ethers by Williamson’s synthesis: 1-Methoxyethane
- Q7.25: Illustrate with examples the limitations of Williamson synthesis for the preparation of certain types of ethers.
- Q7.25: Illustrate with examples the limitations of Williamson synthesis for the preparation of certain types of ethers.
- Q7.26: How is 1-propoxypropane synthesised from propan-1-ol? Write mechanism of this reaction.
- Q7.26: How is 1-propoxypropane synthesised from propan-1-ol? Write mechanism of this reaction.
- Q7.27: Preparation of ethers by acid dehydration of secondary or tertiary alcohols is not a suitable method. Give reason.
- Q7.27: Preparation of ethers by acid dehydration of secondary or tertiary alcohols is not a suitable method. Give reason.
- Q7.28 (i): Write the equation of the reaction of hydrogen iodide with: 1-propoxypropane
- Q7.28 (ii): Write the equation of the reaction of hydrogen iodide with: methoxybenzene
- Q7.28 (iii): Write the equation of the reaction of hydrogen iodide with: benzyl ethyl ether.
- Q7.28(i): Write the equation of the reaction of hydrogen iodide with: 1-propoxypropane
- Q7.28(ii): Write the equation of the reaction of hydrogen iodide with: methoxybenzene
- Q7.28(iii): Write the equation of the reaction of hydrogen iodide with: benzyl ethyl ether.
- Q7.29: Explain the fact that in aryl alkyl ethers (i) the alkoxy group activates the benzene ring towards electrophilic substitution and (ii) it directs the incoming substituents to ortho and para positions in benzene ring.
- Q7.3 (i): Draw the structures of all isomeric alcohols of molecular formula \(C_{5}H_{12}O\) and give their IUPAC names.
- Q7.3 (ii): Classify the isomers of alcohols as primary, secondary and tertiary alcohols.
- Q7.3(i): Draw the structures of all isomeric alcohols of molecular formula ((C_{5}H_{12}O)) and give their IUPAC names.
- Q7.3(ii): Classify the isomers of alcohols as primary, secondary and tertiary alcohols.
- Q7.30: Write the mechanism of the reaction of \(HI\) with methoxymethane.
- Q7.30: Write the mechanism of the reaction of HI with methoxymethane.
- Q7.31 (i): Write equations of the following reactions: Friedel-Crafts reaction – alkylation of anisole.
- Q7.31 (ii): Write equations of the following reactions: Nitration of anisole.
- Q7.31 (iii): Write equations of the following reactions: Bromination of anisole in ethanoic acid medium.
- Q7.31 (iv): Write equations of the following reactions: Friedel-Craft’s acetylation of anisole.
- Q7.31(i): Write equations of the following reactions: Friedel-Crafts reaction – alkylation of anisole.
- Q7.31(ii): Write equations of the following reactions: Nitration of anisole.
- Q7.31(iii): Write equations of the following reactions: Bromination of anisole in ethanoic acid medium.
- Q7.31(iv): Write equations of the following reactions: Friedel-Craft’s acetylation of anisole.
- Q7.32: Show how would you synthesise the following alcohols from appropriate alkenes?
- Q7.32: Show how would you synthesise the following alcohols from appropriate alkenes?
- Q7.32: Show how would you synthesise the following alcohols from appropriate alkenes?
- Q7.32: Show how would you synthesise the following alcohols from appropriate alkenes?
- Q7.32(i): Show how would you synthesise the following alcohols from appropriate alkenes?
- Q7.32(ii): Show how would you synthesise the following alcohols from appropriate alkenes?
- Q7.32(iii): Show how would you synthesise the following alcohols from appropriate alkenes?
- Q7.32(iv): Show how would you synthesise the following alcohols from appropriate alkenes?
- Q7.33: When 3-methylbutan-2-ol is treated with HBr, the following reaction takes place: Give a mechanism for this reaction. (Hint : The secondary carbocation formed in step II rearranges to a more stable tertiary carbocation by a hydride ion shift from 3rd carbon atom.
- Q7.33: When 3-methylbutan-2-ol is treated with HBr, the following reaction takes place: Give a mechanism for this reaction. (Hint : The secondary carbocation formed in step II rearranges to a more stable tertiary carbocation by a hydride ion shift from ((3^{rd})) carbon atom.)
- Q7.4: Explain why propanol has higher boiling point than that of the hydrocarbon, butane?
- Q7.4: Explain why propanol has higher boiling point than that of the hydrocarbon, butane?
- Q7.5: Alcohols are comparatively more soluble in water than hydrocarbons of comparable molecular masses. Explain this fact.
- Q7.5: Alcohols are comparatively more soluble in water than hydrocarbons of comparable molecular masses. Explain this fact.
- Q7.6: What is meant by hydroboration-oxidation reaction? Illustrate it with an example.
- Q7.6: What is meant by hydroboration-oxidation reaction? Illustrate it with an example.
- Q7.7: Give the structures and IUPAC names of monohydric phenols of molecular formula, \(C_{7}H_{8}O\).
- Q7.7: Give the structures and IUPAC names of monohydric phenols of molecular formula, ((C_{7}H_{8}O)).
- Q7.8: While separating a mixture of ortho and para nitrophenols by steam distillation, name the isomer which will be steam volatile. Give reason.
- Q7.8: While separating a mixture of ortho and para nitrophenols by steam distillation, name the isomer which will be steam volatile. Give reason.
- Q7.9: Give the equations of reactions for the preparation of phenol from cumene.
- Q7.9: Give the equations of reactions for the preparation of phenol from cumene.
CBSE Solutions for Class 12 Chemistry Alcohols
Chapters in CBSE - Class 12 Chemistry
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