11- ALCOHALS, PHENOLS AND ETHERS


Here we are going through the ncert solutions for class 12 chemistry chapter 11 – alcohals phenols and ether . so before going through the ncert solutions make sure to go through the textbook that helps you to understand the solutions more easily

 ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ Chapter 11 - Alcohols, Phenols And Ethers

 

 ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​ ​​​​ INTEXT ANSWERS

 

Question 11.1:

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

(i)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5883/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_3eba5a72.jpg

(ii) https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5883/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_4480daa3.jpg

(iii) https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5883/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_9c30609.jpg

(iv)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5883/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_m41e5498.jpg

(v)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5883/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_4649f4df.jpg

(vi)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5883/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_m187f7826.jpg

ANSWER:

Primary alcohol → (i), (ii), (iii)

Secondary alcohol → (iv), (v)

Tertiary alcohol → (vi)

 

Question 11.2:

Identify allylic alcohols in the above examples.

ANSWER:

The​​ alcohols given in (ii) and (vi) are allylic alcohols.



Question 11.3:

Name the following compounds according to IUPAC system.

(i)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5885/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_2afd1234.jpg

(ii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5885/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_5352af0e.jpg

(iii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5885/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_3ac3663e.jpg

(iv)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5885/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_6bac1636.jpg

(v)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5885/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_m2effa79f.jpg

ANSWER:

(i) 3-Chloromethyl-2-isopropylpentan-1-ol

(ii) 2, 5-Dimethylhexane-1, 3-diol

(iii) 3-Bromocyclohexanol

(iv) Hex-1-en-3-ol

(v) 2-Bromo-3-methylbut-2-en-1-ol


Question 11.4:

Show how are the following alcohols prepared by the reaction of a suitable

Grignard reagent on methanal?

(i)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5886/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_465c3cc7.jpg

(ii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5886/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_m472de6ea.jpg

ANSWER:

(i)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5886/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_134675c.jpg

(ii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5886/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_m58022bb3.jpg

 

Question 11.5:

Write​​ structures of the products of the following reactions:

(i)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5887/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_m28469f48.jpg

(ii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5887/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_28b31455.jpg

(iii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5887/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_m2c2fb23d.jpg

ANSWER:

(i)

 

https://img-nm.mnimgs.com/img/study_content/content_ck_images/images/3%20(2).png

(ii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5887/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_m782cd1cf.jpg

(iii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5887/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_m2f33774e.jpg


Question 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

ANSWER:

(a)

(i)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5888/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_6eb4c42a.gif

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

(ii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5888/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_m4d24dc31.jpg

Tertiary alcohols react immediately with Lucas’ reagent.

(b)

(i)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5888/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_d85e47a.gif

(ii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5888/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_6c1929e4.jpg

(c)

(i)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5888/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_m1c4aab5b.gif

(ii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5888/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_m38e4e1c9.jpg

 

Question 11.7:

Predict the major product of acid catalysed dehydration of

(i) 1-Methylcyclohexanol and

(ii) Butan-1-ol

ANSWER:

  •  

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5889/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_m489c21ee.jpg

(ii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5889/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_m11920ce1.gif

 

Question 11.8:

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

ANSWER:

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5890/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_4969df05.jpg

Resonance structure of the phenoxide ion

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5890/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_m238cc3e6.jpg

Resonance structures of p-nitrophenoxide ion

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5890/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_m2b7eb666.jpg

Resonance structures of o-nitrophenoxide ion

It can be observed that the presence of nitro groups increases the stability of​​ phenoxide ion.

 

Question 11.9:

Write the equations involved in the following reactions:

(i) Reimer-Tiemann reaction

(ii) Kolbe’s reaction

ANSWER:

  • Reimer-Tiemann reaction

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5891/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_m7c3f060f.jpg

  • Kolbe’s reaction

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5891/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_m3db4662d.jpg



Question 11.10:

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

ANSWER:

In Williamson synthesis, an alkyl halide reacts with an alkoxide ion. Also, it is an SN2 reaction. In the reaction, alkyl halides should be primary having the least steric​​ hindrance. Hence, an alkyl halide is obtained from ethanol and alkoxide ion from 3-methylpentan-2-ol.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5892/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_m21c11564.gif

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5892/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_6c8640ce.jpg

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5892/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_1a2b25f6.jpg

 

Question 11.11:

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

(i)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5893/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_79ef8b31.jpg

(ii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5893/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_m3776b39a.jpg

ANSWER:

Set (ii) is an appropriate set of reactants for the preparation of 1-methoxy-4-nitrobenzene.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5893/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_m1ce8e46d.jpg

In set (i), sodium methoxide (CH3ONa) is a strong nucleophile as well as a strong base. Hence, an elimination reaction predominates over a substitution​​ reaction.



Question 11.12:

Predict the products of the following reactions:

(i) https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5894/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_30ab4089.gif

(ii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5894/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_38cf5ad8.jpg

(iii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5894/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_760a9be0.jpg

(iv) https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5894/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_4afe6ded.gif

ANSWER:

(i)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5894/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_71425aee.gif

(ii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5894/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_63c5ba52.jpg

(iii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5894/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_m4fd657dc.jpg

(iv)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5894/NS_25-11-08_Utpal_12_Chemistry_11_12_GSX_html_67552236.gif



EXERCISE ANSWERS

 

Question 11.1:

Write IUPAC names of the following compounds:

(i)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5851/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_22ef776e.jpg

(ii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5851/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_325f8b3d.jpg

(iii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5851/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_m497ebc9f.jpg

(iv)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5851/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_4f9bf86e.jpg

(v)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5851/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_63178557.jpg

(vi)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5851/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_m22f6b68.jpg

(vii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5851/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_m326f6c2f.jpg

(viii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5851/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_m555ef319.jpg

(ix)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5851/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_m5574e30c.jpg

(x) https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5851/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_m52b8292.gif

(xi) https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5851/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_m2f7cc44a.gif

(xii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5851/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_6e3ba14a.jpg

ANSWER:

(i) 2, 2, 4-Trimethylpentan-3-ol

(ii) 5-Ethylheptane-2, 4-diol

(iii) Butane-2, 3-diol

(iv) Propane-1, 2, 3-triol

(v) 2-Methylphenol

(vi) 4-Methylphenol

(vii) 2, 5-Dimethylphenol

(viii) 2,​​ 6-Dimethylphenol

(ix) 1-Methoxy-2-methylpropane

(x) Ethoxybenzene

(xi) 1-Phenoxyheptane

(xii) 2-Ethoxybutane

 

Question 11.2:

Write structures of the compounds whose IUPAC names are as follows:

(i) 2-Methylbutan-2-ol

(ii) 1-Phenylpropan-2-ol

(iii) 3,5-Dimethylhexane −1, 3, 5-triol

(iv) 2,3 − Diethylphenol

(v) 1 − Ethoxypropane

(vi) 2-Ethoxy-3-methylpentane

(vii) Cyclohexylmethanol

(viii) 3-Cyclohexylpentan-3-ol

(ix) Cyclopent-3-en-1-ol

(x) 3-Chloromethylpentan-1-ol.

ANSWER:

(i)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5852/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_1026f97.jpg

(ii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5852/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_mdc6572b.jpg

(iii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5852/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_m7263149a.jpg

(iv)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5852/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_dc03a33.jpg

(v)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5852/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_6b094b12.gif

(vi)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5852/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_5b0e14da.jpg

(vii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5852/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_m70c65f0b.jpg

(viii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5852/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_3cb48a19.jpg

(ix)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5852/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_78361613.jpg

(x)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5852/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_503aa0af.jpg

 

Question 11.3:

(i) Draw the structures of all isomeric alcohols of molecular formula C5H12O and give their IUPAC names.

(ii) Classify the isomers of alcohols in question 11.3 (i) as primary, secondary and​​ tertiary alcohols.

ANSWER:

(i) The structures of all isomeric alcohols of molecular formula, C5H12O are shown below:

(a) https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5869/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_7ffa6f4d.gif

Pentan-1-ol (1°)

(b)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5869/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_7695e19b.jpg

2-Methylbutan-1-ol (1°)

(c)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5869/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_72285cf.jpg

3-Methylbutan-1-ol (1°)

(d)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5869/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_2eb5fb30.jpg

2, 2-Dimethylpropan-1-ol (1°)

(e)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5869/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_47188706.jpg

Pentan-2-ol​​ (2°)

(f)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5869/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_m322b84ff.jpg

3-Methylbutan-2-ol (2°)

(g)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5869/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_705c3b37.jpg

Pentan-3-ol (2°)

(h)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5869/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_m4fee7e8b.jpg

2-Methylbutan-2-ol (3°)

(ii) Primary alcohol: Pentan-1-ol; 2-Methylbutan-1-ol;

3-Methylbutan-1-ol; 2, 2−Dimethylpropan-1-ol

Secondary alcohol: Pentan-2-ol; 3-Methylbutan-2-ol;

Pentan-3-ol

Tertiary alcohol: 2-methylbutan-2-ol

 

Question 11.4:

Explain why propanol has higher boiling point than that of the hydrocarbon, butane?

ANSWER:

Propanol undergoes intermolecular H-bonding because of the presence of −OH group. On the other hand, butane does​​ not

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5854/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_27520688.jpg

Therefore, extra energy is required to break hydrogen bonds. For this reason, propanol has a higher boiling point than hydrocarbon butane.

 

Question 11.5:

Alcohols are comparatively more soluble in water than hydrocarbons of comparable molecular masses. Explain this fact.

ANSWER:

Alcohols form H-bonds with water due to the presence of −OH group. However, hydrocarbons cannot form H-bonds with water.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5855/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_mf63c515.jpg

As a result, alcohols are comparatively more soluble in water than hydrocarbons of comparable​​ molecular masses.

 

Question 11.6:

What is meant by hydroboration-oxidation reaction? Illustrate it with an example.

ANSWER:

The addition of borane followed by oxidation is known as the hydroboration-oxidation reaction. For example, propan-1-ol is produced​​ by the hydroboration-oxidation reaction of propene. In this reaction, propene reacts with diborane (BH3)2 to form trialkyl borane as an addition product. This addition product is oxidized to alcohol by hydrogen peroxide in the presence of aqueous sodium​​ hydroxide.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5875/NS_25-11-08_Utpal_12_Chemistry_11_8_GSX_html_m50c385e7.jpg

 

Question 11.7:

Give the structures and IUPAC names of monohydric phenols of molecular formula, C7H8O.

ANSWER:

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5857/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_10035447.jpg

 

Question 11.8:

While separating a mixture of ortho and para nitrophenols by steam distillation, name the isomer which will be​​ steam volatile. Give reason.

ANSWER:

Intramolecular H-bonding is present in o-nitrophenol. In p-nitrophenol, the molecules are strongly associated due to the presence of intermolecular bonding. Hence, o-nitrophenol is steam volatile.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5858/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_m3400c57.jpg

 

Question 11.9:

Give​​ the equations of reactions for the preparation of phenol from cumene.

ANSWER:

To prepare phenol, cumene is first oxidized in the presence of air of cumene hydro-peroxide.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5859/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_344e7fc6.jpg

Then, cumene hydroxide is treated with dilute acid to prepare phenol and acetone​​ as by-products.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5859/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_510918fe.jpg

 

Question 11.10:

Write chemical reaction for the preparation of phenol from chlorobenzene.

ANSWER:

Chlorobenzene is fused with NaOH (at 623 K and 320 atm pressure) to produce sodium phenoxide, which gives phenol on acidification.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5861/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_m28df612c.jpg

 

Question 11.11:

Write the mechanism of hydration of ethene to yield ethanol.

ANSWER:

The mechanism of hydration of ethene to form ethanol involves three steps.

Step 1:

Protonation of ethene to form carbocation by electrophilic attack of H3O+:

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5876/NS_25-11-08_Utpal_12_Chemistry_11_8_GSX_html_1f35a9a.jpg

Step 2:

Nucleophilic attack of water on carbocation:

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5876/NS_25-11-08_Utpal_12_Chemistry_11_8_GSX_html_1331990.jpg

Step 3:

Deprotonation to form ethanol:

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5876/NS_25-11-08_Utpal_12_Chemistry_11_8_GSX_html_32aef1b3.jpg

 

Question 11.12:

You are given benzene, conc. H2SO4 and NaOH. Write the equations for the preparation of phenol using these reagents.

ANSWER:

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5864/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_7bf3042e.jpg



Question 11.13:

Show​​ how will you synthesize:

(i) 1-phenylethanol from a suitable alkene.

(ii) cyclohexylmethanol using an alkyl halide by an SN2 reaction.

(iii) pentan-1-ol using a suitable alkyl halide?

ANSWER:

(i) By acid-catalyzed hydration of ethylbenzene (styrene), 1-phenylethanol can be synthesized.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5832/NCERT_26-11-08_Utpal_12_Chemistry_11_11_GSX_html_m3f1a5714.jpg

(ii) When chloromethylcyclohexane is treated with sodium hydroxide, cyclohexylmethanol is obtained.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5832/NCERT_26-11-08_Utpal_12_Chemistry_11_11_GSX_html_22e27f01.jpg

(iii) When 1-chloropentane is treated with NaOH, pentan-1-ol is produced.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5832/NCERT_26-11-08_Utpal_12_Chemistry_11_11_GSX_html_m523876d.gif

 

Question 11.14:

Give two reactions that show​​ the acidic nature of phenol. Compare acidity of phenol with that of ethanol.

ANSWER:

The acidic nature of phenol can be represented by the following two reactions:

(i) Phenol reacts with sodium to give sodium phenoxide, liberating H2.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5833/NCERT_26-11-08_Utpal_12_Chemistry_11_11_GSX_html_17ab1f91.jpg

(ii) Phenol reacts​​ with sodium hydroxide to give sodium phenoxide and water as by-products.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5833/NCERT_26-11-08_Utpal_12_Chemistry_11_11_GSX_html_m206fb24f.jpg

The acidity of phenol is more than that of ethanol. This is because after losing a proton, the phenoxide ion undergoes resonance and gets stabilized whereas ethoxide ion does not.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5833/NCERT_26-11-08_Utpal_12_Chemistry_11_11_GSX_html_dc05edb.jpg

 

Question 11.15:

Explain why is ortho nitrophenol more acidic than ortho methoxyphenol?

ANSWER:

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5834/NCERT_26-11-08_Utpal_12_Chemistry_11_11_GSX_html_m3ba5f81e.jpg

The nitro-group is an electron-withdrawing group. The presence of this group in the ortho position decreases the electron density in the O−H bond. As a​​ result, it is easier to lose a proton. Also, the o-nitrophenoxide ion formed after the loss of protons is stabilized by 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 in the O−H bond and hence, the proton cannot be given out easily.

For this reason, ortho-nitrophenol is more acidic than ortho-methoxyphenol.

 

Question 11.16:

Explain how does the −OH group attached to a carbon of benzene ring activate it towards electrophilic substitution?

ANSWER:

The −OH group is an electron-donating group. Thus, it increases the electron density in the benzene ring as shown in the given resonance structure of phenol.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5835/NCERT_26-11-08_Utpal_12_Chemistry_11_11_GSX_html_3373216b.jpg

As a result, the benzene ring is activated towards electrophilic substitution.

 

Question 11.17:

Give equations of the following reactions:

(i) Oxidation of propan-1-ol with alkaline KMnO4 solution.

(ii) Bromine in CS2 with phenol.

(iii) Dilute HNO3 with phenol.

(iv) Treating phenol with​​ chloroform in presence of aqueous NaOH.

ANSWER:

(i) https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5880/NS_25-11-08_Utpal_12_Chemistry_11_8_GSX_html_m43670e1e.gif

(ii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5880/NS_25-11-08_Utpal_12_Chemistry_11_8_GSX_html_m325734.jpg

(iii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5880/NS_25-11-08_Utpal_12_Chemistry_11_8_GSX_html_m4c697bd4.jpg

(iv)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5880/NS_25-11-08_Utpal_12_Chemistry_11_8_GSX_html_mb7235e4.jpg

 

Question 11.18:

Explain the following with an example.

(i) Kolbe’s reaction.

(ii) Reimer-Tiemann reaction.

(iii) Williamson ether synthesis.

(iv) Unsymmetrical ether.

ANSWER:

(i) Kolbe’s reaction:

When phenol is treated with sodium hydroxide, sodium phenoxide is produced. This sodium phenoxide when treated with carbon dioxide, followed by acidification, undergoes electrophilic substitution to give ortho-hydroxybenzoic acid as the main product. This reaction is known as Kolbe’s reaction.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5836/NCERT_26-11-08_Utpal_12_Chemistry_11_11_GSX_html_m59d450ff.jpg

(ii) Reimer-Tiemann reaction:

When phenol is treated with chloroform (CHCl3) in the presence of sodium hydroxide, a −CHO group is introduced at the ortho position of the benzene ring.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5836/NCERT_26-11-08_Utpal_12_Chemistry_11_11_GSX_html_m1825c3f5.jpg

This​​ reaction is known as the Reimer-Tiemann reaction.

The intermediate is hydrolyzed in the presence of alkalis to produce salicyclaldehyde.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5836/NCERT_26-11-08_Utpal_12_Chemistry_11_11_GSX_html_m2bda19d7.jpg

(iii) Williamson ether synthesis:

Williamson ether synthesis is a laboratory method to prepare symmetrical and unsymmetrical ethers by allowing alkyl halides to react with sodium alkoxides.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5836/NCERT_26-11-08_Utpal_12_Chemistry_11_11_GSX_html_3a0ab0ad.jpg

This reaction involves SN2 attack of the alkoxide ion on the alkyl halide. Better results are obtained in case of primary alkyl halides.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5836/NCERT_26-11-08_Utpal_12_Chemistry_11_11_GSX_html_m423ad888.jpg

If the alkyl halide is secondary or tertiary, then elimination competes over substitution.

(iv) Unsymmetrical ether:

An unsymmetrical ether is an ether where two groups on the two sides of an oxygen atom differ (i.e., have an unequal number of carbon atoms). For example: ethyl methyl ether (CH3−O−CH2CH3).

 

Question 11.19:

Write the mechanism of acid-catalysed dehydration of ethanol to yield ethene.

ANSWER:

The mechanism of acid dehydration of ethanol to yield ethene involves the following three steps:

Step 1:

Protonation of ethanol to form ethyl​​ oxonium ion:

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5879/NS_25-11-08_Utpal_12_Chemistry_11_8_GSX_html_3676e20a.jpg

Step 2:

Formation of carbocation (rate determining step):

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5879/NS_25-11-08_Utpal_12_Chemistry_11_8_GSX_html_1d145240.jpg

Step 3:

Elimination of a proton to form ethene:

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5879/NS_25-11-08_Utpal_12_Chemistry_11_8_GSX_html_m333d7217.jpg

The acid consumed in step 1 is released in Step 3. After the formation of ethene, it is removed to shift the equilibrium in a​​ forward direction.

 

Question 11.20:

How are the following conversions carried out?

(i) Propene → Propan-2-ol

(ii) Benzyl chloride → Benzyl alcohol

(iii) Ethyl magnesium chloride → Propan-1-ol.

(iv) Methyl magnesium bromide → 2-Methylpropan-2-ol.

ANSWER:

(i) If propene is allowed to react with water in the presence of an acid as a catalyst, then propan-2-ol is obtained.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5837/NCERT_26-11-08_Utpal_12_Chemistry_11_11_GSX_html_m27bc4b33.jpg

(ii) If benzyl chloride is treated with NaOH (followed by acidification) then benzyl alcohol is produced.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5837/NCERT_26-11-08_Utpal_12_Chemistry_11_11_GSX_html_m668c5cdc.jpg

(iii) When ethyl magnesium chloride is treated with methanal, an adduct is the produced which gives propan-1-ol on hydrolysis.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5837/NCERT_26-11-08_Utpal_12_Chemistry_11_11_GSX_html_m74382e01.jpg

(iv) When methyl magnesium bromide is treated with propane, an adduct is the product which gives 2-methylpropane-2-ol on hydrolysis.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5837/NCERT_26-11-08_Utpal_12_Chemistry_11_11_GSX_html_35785c74.jpg

 

Question 11.21:

Name the reagents used in the following reactions:

(i) Oxidation of a primary alcohol to carboxylic acid.

(ii) Oxidation of a primary alcohol to aldehyde.

(iii) Bromination of phenol to 2,4,6-tribromophenol.

(iv) Benzyl alcohol to benzoic acid.

(v) Dehydration of propan-2-ol to propene.

(vi) Butan-2-one to butan-2-ol.

ANSWER:

(i) Acidified potassium permanganate

(ii) Pyridinium chlorochromate (PCC)

(iii) Bromine water

(iv) Acidified potassium permanganate

(v) 85% phosphoric acid

(vi) NaBH4 or LiAlH4

 

Question 11.22:

Give reason for the higher boiling point of ethanol in comparison to methoxymethane.

ANSWER:

Ethanol undergoes intermolecular H-bonding due to the presence of −OH group, resulting in the association of molecules. Extra energy is required to​​ break these hydrogen bonds. On the other hand, methoxymethane does not undergo H-bonding. Hence, the boiling point of ethanol is higher than that of methoxymethane.

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5865/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_4a5e43c.jpg



 

Question 11.23:

Give IUPAC names of the following ethers:

(i)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5868/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_481f47fa.jpg

(ii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5868/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_m1f90bfb9.jpg

(iii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5868/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_m1946919b.jpg

(iv)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5868/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_3d56305c.jpg

(v)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5868/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_6bb5423b.jpg

(vi)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5868/NS_24-11-08_Utpal_12_Chemistry_11_12_GSX_html_5f95f1f1.jpg

ANSWER:

(i) 1-Ethoxy-2-methylpropane

(ii) 2-Chloro-1-methoxyethane

(iii) 4-Nitroanisole

(iv) 1-Methoxypropane

(v) 1-Ethoxy-4, 4-dimethylcyclohexane

(vi) Ethoxybenzene

 

Question 11.24:

Write the names of reagents and equations for the​​ preparation of the following ethers by Williamson’s synthesis:

(i) 1-Propoxypropane

(ii) Ethoxybenzene

(iii) 2-Methoxy-2-methylpropane

(iv) 1-Methoxyethane

ANSWER:

(i) https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5878/NS_25-11-08_Utpal_12_Chemistry_11_8_GSX_html_mcb9ae7c.gif

(ii)

https://img-nm.mnimgs.com/img/study_content/curr/1/12/17/270/5878/NS_25-11-08_Utpal_12_Chemistry_11_8_GSX_html_45d4a126.jpg

(iii)