Class 12 Chemistry Notes Chapter 11 Alcohols, Phenols and Ethers

Alcohols, Phenols and Ethers Class 12 Chemistry Notes

11.1 Classify the following as primary, secondary and tertiary alcohols:

primary, secondary and tertiary alcohols

Ans:

  1. Primary alcohol
  2. Primary alcohol
  3. Primary alcohol
  4. Secondary alcohol
  5. Secondary alcohol
  6. Tertiary alcohol

11.2 Identify allylic alcohols in the above examples.

Ans: (ii) and (iv) i.e. H2C=CH – CH2OH and

allylic alcohols

11.3 Name the following compounds according to IUPAC system

IUPAC system

Ans:

  1. 3-Chloromethyl-2-isopropylpentan-1-ol
  2. 2, 5-Dimethylhexane-1, 3-diol
  3. 3-Bromocyclohexanol
  4. Hex-1-en-3-ol
  5. 2-Bromo-3-methylbut-2-en-1-ol

11.4 Show how are the following alcohols prepared by the reaction of a suitable Grignard reagent on methanol?

Grignard reagent on methanol

Ans:

(i) Grignard reagent that reacts with methanol is isopropyl magnesium halide

Grignard reagent on methanol

(ii)

Grignard reagent on methanol

11.5 Write structures of the products of the following reactions:

Alcohols, Phenols and Ethers

Ans:

(i)

Alcohols, Phenols and Ethers

(ii)

Alcohols, Phenols and Ethers

(iii)

Alcohols, Phenols and Ethers

11.6 Give structures of the products you would expect when each of the following alcohol reacts with
(a) HCl –ZnCl2 (b) HBr and (c) SOCl2 .
(i) Butan-1-ol (ii) 2-Methylbutan-2-ol

Ans: (a) (i) Primary alcohols do not react appreciably with Lucas’ reagent (HCl-ZnCl2) at room temperature.

Lucas’ reagent

(ii)

Lucas’ reagent

(b) (i)

HBr

(ii)

(c)(i)

(ii)

11.7 Predict the major product of acid catalysed dehydration of
(i) 1-methylcyclohexanol and (ii) butan-1-ol

Ans: (i) Acid catalysed dehydration of 1-methylcyclohexanol can give two products. However, 1-methylcyclohexene will be  preferably formed according to Satyzeff s rule since it is more substituted.

acid catalysed dehydration of 1-methylcyclohexanol

(ii)

acid catalysed dehydration of butan-1-ol

11.8 Ortho and para nitrophenols are more acidic than phenol. Draw the resonance structures of the corresponding phenoxide ions.

Ans: The attachment of the -NO2 group to the phenol molecule at 0- and p-positions decreases the electron density on oxygen atom. This causes the oxygen atom to pull the bond pair of electrons of the O – H bond towards itself thereby facilitating the release of H as H+.

The resonance structures of the phenoxide ions are:

resonance structures of the phenoxide ions

Resonance structures of o-nitrophenoxide ion

Resonance structures of o-nitrophenoxide

11.9 Write the equations involved in the following reactions:
(i) Reimer – Tiemann reaction (ii) Kolbe’s reaction

Ans: (i)

Reimer  Tiemann reaction and Kolbe’s reaction

11.10 Write the reactions of Williamson synthesis of 2-ethoxy-3-methylpentane starting from ethanol and 3-methylpentan-2-ol.

Ans: In the Williamson’s synthesis, the reactants are alkyl halide and sodium salt of an alcohol. In order to avoid the formation of alkene during the reaction, the alkyl halide should be primary while sodium salt must be of branched chain alcohol

Williamson’s synthesis

11.11 Which of the following is an appropriate set of reactants for the preparation of 1-methoxy-4-nitrobenzene and why?

1-methoxy-4-nitrobenzene

Ans: The second set of reactants is more appropriate to give the products i.e., l-methoxy-4-nitrobenzene. In the first set, cleavage of C – Br bond is involved. It is rather difficult since the carbon atom is sp2 hybridised and the bond has partial double bond character as well. The product is formed as a result of Williamson’s synthesis.

1-methoxy-4-nitrobenzene

11.12 Predict the products of the following reactions:

alcohols

(i) This reaction involves the cleavage of C – 0 bond

(ii) The Br atom of HBr is expected to combine with ethyl group

Br atom of HBr

(iii) The ethoxy group (OC2H5) is an activating group and increases the electron density at the ortho and para positions due to +M effect

ethoxy group

(iv) The reaction follows Sn1 mechanism.

Sn1 mechanism

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