CBSE Class 12 Chemistry Alcohols Phenols And Ethers Notes Set B

ALCOHOLS, PHENOLS AND ETHERS

IMPORTANT QUESTIONS

1. Alcohols are comparatively more soluble in water than the hydrocarbons of comparable molecular masses? Explain?
Alcohols can form hydrogen bonds with water and therefore these are soluble whereas hydrocarbon cannot form H-bonding and therefore are insoluble in water.

2. Explain why is orthonitrophenol more acidic than orthomethoxy phenol?
The nitro- is an electron withdrawing group .the presence of this group in the ortho position decreases the electron density .As a result, it is easier to lose a proton. Also the orthonitrophenoxide ion formed is stabilized by the resonance. Hence, ortho nitrophenol is a stronger acid On the other hand, methoxy group is an electron-releasing group. Thus, it increases the electron density. Therefore proton cannot be given out easily. So, ortho nitrophenol more acidic than orthomethoxy phenol.

3. Why lower alcohols soluble in water but higher alcohol not?
Due to the formation H-Bonds lower alcohol are soluble in water. Higher alcohol are less soluble due to the resence of higher alcohols.

4. Why phenols have higher boiling point than arenes?
Due to H-Bonding.

5. Prepare phenol from Diazonium salts?

6.How will you distinguish between primary, secondary and tertiary alcohols?
When primary, secondary, tertiary alcohols are treated with Lucas reagent at room temperature, then 

(i) If turbidity appears immediately, alcohols is tertiary

(ii) If turbidity appears in 5 minutes, alcohols is secondary

(iii) If no reaction, alcohols are primary.
(Lucas reagent is conc.HCl +anhydrous zinc chloride)

7. Phenol is acidic in nature.
Phenol is acidic in nature because:
a) phenol , due to resonance, the positive charge rests on oxygen making the shared pair of electrons more towards oxygen and hydrogen as H+

b) The carbon attached to OH is SP2 hybridize and is more electronegative, this decreases the electron density on oxygen, increasing the polarity of O-H bond and ionization of phenol.

c) The phenoxide ion formed by loss of H+ is more resonance stabilized than phenol itself.

8. Diethyl ether does not react with sodium. Explain.
Diethyl ether does not contain any active hydrogen.

9. Write the reaction showing formation of aspirin?

10. What is the main product obtained when vapors of t-butyl alcohol are passed over Copper at 300°C ?
Ans. It undergoes dehydration to form 2- Methylpropene.

11. Phenol has smaller dipole moment than methanol. Why?
Ans. Due to the electron withdrawing effect of phenyl group present in contrast to the electron releasing group present in alcohols.

12. Why are Grignard reagents soluble in ether but not in benzene?
Ans. Because being polar nature of both ether as well as of Grignard reagents ,but benzene is non polar solvent . 

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