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-} {O}\underset{C_3 H _7}{|} .........\overset{\delta+}{H} -\overset{\delta-} {O}\underset{C_3 H _7}{|} ........\overset{\delta+}{H} -\overset{\delta-} {O}\underset{C_3 H _7}{|}$$\\$ Therefore, extra energy is required to break hydrogen bonds. For this reason, propanol has a higher boiling point than hydrocarbon butane.

5   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.