Alcohols Phenols and Ethers

Chemistry

NCERT

1   Write $IUPAC$ names of the following compounds.

Solution :

(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$\\$

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.

Solution :

3   (i) Draw the structures of all isomeric alcohols of molecular formula $C _5 H _{12 }O $and give their $IUPAC$ names.$\\$ (ii) Classify the isomers of alcohols in question 11.3 (i) as primary, secondary and tertiary alcohols.

Solution :

(i) The structures of all isomeric alcohols of molecular formula, $C _5 H _{12} O$ are shown below:$\\$ (a)$CH_3-CH_2-CH_2-CH_2-CH_2-OH$$\\$ Pentan-1-ol($1^o)$$\\$ (b)$CH_3-CH_2-\underset{\underset{CH_{3}}{|}}CH-CH_2-OH$$\\$ 2-Methylbutan-1-ol($1^o$)$\\$

(c)$CH_3-\underset{\underset{CH_3}{|}}{CH}-CH_2-CH_2-OH$$\\$ 3-Methylbutan-1-ol($1^o)$$\\$ (d)$CH_3-{\underset{CH_3}{|}}{\overset{CH_3}{|}}{C}-CH_2-OH$$\\$ $2, 2-$Dimethylpropan$-1-$ol ($ 1^o)$$\\$ (e)$CH_3-CH_2-CH_2-\overset{\overset{OH}{|}}{CH}-CH_3$$\\$ Pentan-2-ol($2^o$)$\\$

(f)$CH_3-\overset{\overset{CH_3}{|}}{CH}-\overset{\overset{OH}{|}}{CH}-CH_3$$\\$ 3-Methylbutan-2-ol($2^o$)$\\$ (g)$CH_3-CH_2-\overset{\overset{OH}{|}}{CH}-CH_2-CH_3$$\\$ Pentan-3-ol($2^o$)$\\$

(h)

$2-$Methylbutan$-2-$ol $( 3^o)$$\\$ (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$\\$

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

Solution :

Propanol undergoes intermolecular H-bonding because of the presence of —OH group. On the other hand, butane does not$\\$ $.....\overset{\delta+}{H} -\overset{\delta-} {\underset{\underset{C_3 H _7}{|}}{O}} .........\overset{\delta+}{H} -\overset{\delta-}{\underset{\underset{C_3 H _7}{|}}{O}} ........\overset{\delta+}{H} -\overset{\delta-}{\underset{\underset{C_3 H _7}{|}}{O}}$ $\\$ Therefore, extra energy is required to break hydrogen bonds. For this reason, propanol has a higher boiling point than hydrocarbon butane.

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

Solution :

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

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

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

Solution :

The addition of borane followed by oxidation is known as the hydroboration-oxidation reaction, For example, propan-l-ol is produced by the hydroboration-oxidation reaction of propene. In this reaction, propene reacts with diborane $(BH _3 )_ 2$ to form trialkylborane as an addition product. This addition product is oxidized to alcohol by hydrogen peroxide in the presence of aqueous sodium hydroxide.

7   Give the structures and $IUPAC$ names of monohydric phenols of molecular formula, $C_ 7 H _8 O .$

Solution :

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

Solution :

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

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

Solution :

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

To prepare phenol, cumene is first oxidized in the presence of air of cumene hydroperoxide.

10   Write chemical reaction for the preparation of phenol from chlorobenzene.

Solution :

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