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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 :
Step 1: Theoretical Foundation of Resonance in Alkoxybenzenes
Aryl alkyl ethers, specifically alkoxybenzene ($C_6H_5-OR$, where $R$ is an alkyl group), exhibit unique electronic effects due to the presence of the oxygen atom directly bonded to the aromatic ring. The oxygen atom possesses two lone pairs of electrons, one of which participates in $p\pi-p\pi$ conjugation with the $\pi$-system of the benzene ring.
Step 2: Analysis of Ring Activation (Electrophilic Substitution)
The $+R$ (resonance) effect of the alkoxy group ($-OR$) increases the electron density within the benzene ring. This phenomenon is visualized through the delocalization of the lone pair on oxygen into the aromatic pi-system [Per Resonance Theory].
- The oxygen atom donates electron density to the ring via resonance.
- This increase in electron density makes the ring more nucleophilic.
- Consequently, the ring becomes more susceptible to attack by electrophiles ($E^+$) compared to benzene itself [Ref: Electrophilic Aromatic Substitution (EAS) mechanism].
Step 3: Directing Influence (Ortho and Para Orientation)
The resonance stabilization of the intermediate sigma-complex (arenium ion) determines the orientation of the incoming substituent. Analyzing the resonance structures of an alkoxybenzene:
By drawing canonical structures, we observe that the negative charge is distributed at the ortho and para positions:
| Resonance Position | Electronic Status | Consequence |
|---|---|---|
| Ortho ($o$) | High electron density | Favored for $E^+$ attack |
| Meta ($m$) | Low electron density | Disfavored |
| Para ($p$) | High electron density | Favored for $E^+$ attack |
Step 4: Conclusion of Mechanism
The transition state for the electrophilic attack at the ortho and para positions is significantly stabilized by the $+R$ effect of the $-OR$ group. This stabilization lowers the activation energy for ortho and para substitution relative to meta substitution [Per Transition State Theory].
Final Solution: The alkoxy group ($-OR$) acts as an activating group due to its $+R$ effect, which increases electron density within the benzene ring. Furthermore, because this resonance effect specifically concentrates negative charge at the ortho and para positions, these positions become the most reactive sites for incoming electrophiles, effectively directing them to those locations.
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.
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