Ncert Solutions Chemistry Class 12th

11.22

There are many ways to this conversion. Two of them are given below:-

(a) In the above conversion, the chlorobenzene is treated with a base such as NaOH, KOH etc. (strong base). The base abstracts the hydrogen from the C-2 position (it can also abstract the hydrogen from the C-6 position, as both are equally acidic) leaving the negative charge at that position.

In the next step Cl^- leaves, leaving behind the positive charge at that carbon. Both the negative charge and positive charge forms a bond resulting Benzyne as the intermediate.

After the formation of the Benzyne intermediate OH^- of the base attacks at the C-1 position and further, the H⁺ attacks to stabilize the negative charge thus resulting in the phenol.

The reaction can start from benzene also. Chlorination of benzene gives Chlorobenzene. When it is further treated with NaOH and H₂O at 350°C it results in the formation of sodium phenoxide which on further treatment H⁺ gives Phenol as the final product.

11.18

The hydroboration-oxidation reaction is a two-step reaction that converts an alkene into a neutral alcohol by the net addition of water across the double bond. The hydrogen and hydroxyl group are added in a syn addition leading to the cis configuration. Hydroboration- oxidation is an anti-Markovnikov reaction, with the hydroxyl group attaching to the less substituted carbon. In first step Addition of Hydroborate group is done and in next step, it is oxidized by hydrogen peroxide.

For example: - When propene undergoes hydroboration-oxidation reaction, then it produces propan-1-ol as product. In this reaction diborane i.e., (BH₃)₂ reacts with propene, which in result generates trialkyl borane as an addition product. Then trialkyl borane is oxidised, by using hydrogen peroxide in the presence of aqueous sodium hydroxide to form alcohol, as final product.

11.15

The structures of all isomeric alcohols of C₅H₁₂O are given below:

Naming is done by the conventional method. The -OH group is attached on the first carbon.

(b) 3-Methylbutan-1-ol

Butane is the longest chain and methyl is the substituent group.

(c) 3-Methylbutan-1-ol

the longest chain is butane and conventional naming method is used.

(d) 2,2-Dimethylpropan-1-ol

Isomer is made by transforming the principal carbon into tertiary type. The longest chain is butane and named accordingly.

(e) Pentan-2-ol

the longest chain is pentane and the numbering is chosen from the minimum position.

Butane is the longest chain, further numbering is done by choosing a minimum position for the

-OH group followed by other substituents.

(g) Pentan-3-ol

Conventional method of naming is used.

(h) 2-Methylbutan-2-ol

Butane is the longest chain and substituents are named accordingly by looking into minimum position.

(f) 3-Methylbutan-2-ol

Butane is the longest chain, further numbering is done by choosing a minimum position for the

-OH group followed by other substituents.

(g) Pentan-3-ol

Conventional method of naming is used.

(h) 2-Methylbutan-2-ol

Butane is the longest chain and substituents are named accordingly by looking into minimum position.

11.14

Butane is the longest chain.

Propane is principle chain and substituents are numbered accordingly.

Hexane is the longest chain. There are three -OH substituents and 2 methyl groups.

-OH of phenol is numbered a 1.

Propane is the principle chain and the alkoxy group is ethyl group.

the longest chain is pentane and substituents are numbered accordingly.

In such cases, cyclo groups are named first, followed by conventional naming methods.

The cyclo group is named first, followed by conventional naming methods.

Cyclo group is named first. Pentane having a double bond is named then with the suffix -OL added to the end.

The longest chain is butane when looked for minimum numbering case.

11.13

2,2,4-Trimethylpentan-3-ol

The naming of the compound usually starts with numbering the carbons in the chain. The lower set of locants are chosen for this purpose, while in this case numbering under this condition is done from the left side. Once the carbons are mentioned, the position of -OH group is numbered and -ol is added as the suffix.

2. 5-Ethylheptane-2,4-diol

Here the longest chain is the straight chain. For such situations, numbering should be such that the functional groups should be denoted by the smallest number. Ethyl group is named at the beginning as it's a side chain.

3. Butane-2,3-diol

In this system, glycols are called as Diols and their class name is Alkane diols. The two-hydroxyl group position is indicated by Arabic numerals. Firstly, the carbon chain is named, the -OH positions are numbered and suffixed with -diol (depends on the number of -OH groups.

4. Propane-1,2,3-triol

Initially carbon chain is named, -OH groups are numbered (can be done from any side as it's a symmetrical compound) and suffixed with triol.

5. 2-Methylphenol

In the IUPAC system, the position of the substituent w.r.t –OH group is indicated by an Arabic numeral, with the carbon carrying the OH group being numbered 1. So, methyl is numbered at the minimum position and phenol is added. The common name is o-cresol (ortho-cresol).

6. 4-Methylphenol

Methyl group is numbered 4 w.r.t to -OH position. The compound is symmetrical. The compound is known by its common name p-cresol (para cresol).

7. 2,5-Dimethylphenol

The position of the substituent w.r.t –OH group is indicated by an Arabic numeral, with the carbon carrying the OH group being numbered 1. The lowest number chain is further chosen. The positions of the methyl group is 2 and 5.

8. 1-Methoxy-2-methylpropane 

the longest carbon chain attached to oxygen is chosen. It is called the principal chain and the other carbon chain is named with -oxy (Alkoxy) suffix at the end. Now the position of alkoxy group is 1

w.r.t the principal chain (propane) and the methyl group

Is 2. Further alphabetically methoxy comes before methyl, therefore named as such.

9. Ethoxybenzene

The principal chain is benzene, so the short chain is named as ethoxy and suffixed with benzene

10. 1-Phenoxyheptane

Principal chain is heptane group having 7 carbon groups. Phenol group is called as substituent alkoxy group and is named.

11. 2-Ethoxybutane

The longest chain here is butane and the ethyl group is attached to the 2^nd carbon.