Ncert Solutions Chemistry Class 12th

This is a multiple choice answer as classified in NCERT Exemplar

(IV) o-methoxy phenol

The stability of the conjugate base  determines the acidic character of the compound.  Higher the stability of the conjugate base, the higher is the acidic character.

Phenol, O-nitrophenol, O-methyl phenol, and O-methoxy phenol all are aromatic compounds. In aromatic compounds, the negative charge of the conjugate base charge is delocalised. The delocalisation of negative charge gives additional stability to the compound. 

Ethanol is not aromatic and it cannot delocalise the negative charge formed after the  H⁺ ion leaves the c. So, it is the least acidic among the given options. Thus, we can eliminate it.

There are two types of groups, the electron-withdrawing, and the electron releasing group. The methyl group and the methoxy group are electron releasing groups. They release the electrons and hence decreases the stability of the negatively charged conjugate base.

On the other hand, a nitro group is an electron-withdrawing group. They withdraw the electrons from the aromatic ring. Withdrawing the negative charge from the ring will increase the stability of the compound in this case.

Phenoxide is stabilised by resonance effect only and it does not have any electron releasing group. So, it is more acidic than o-methyl phenol and o-methoxy phenol. But the absence of an electron-withdrawing group makes it less acidic than o-nitrophenol.

This is a multiple choice answer as classified in NCERT Exemplar

(II) 2-methoxy-2-methylethane

IUPAC provides consistency to the names of organic compounds. It enables every compound to possess a unique name, which otherwise is not plausible with the common names. The chemical structure of the given compound is shown below:

The given compound is an alkane so suffix in our case will be –ane. An ether functional group is also present so prefix will be Alkoxy-.

To determine the name of a compound, identify the longest and continuous chain of carbon containing the functional group and count the number of carbon atoms in the chain as shown in the table below.

In the given compound, the number of carbon atoms in the longest chain is 2. That means the prefix of alkane in our case is eth-.

Numbering of the carbons in the longest chain of carbon (Remember that If the organic molecule is not an alkane (and has a functional group) you have to initiate numbering such that the functional group is placed on the carbon having the lowest possible number).

In the given compound, we can number as shown below:

In the given compound, either the group and methyl group present on the second carbon will be treated like a branched group. It will be written as 2-methyl methoxy before the main chain name.

Finally, combine the elements of the compound name in the specified order as: branched groups, prefix, suffix according to the functional group and its location along the longest carbon chain.

Therefore, the given compound will have IUPAC name as: 2-methyl methoxy ethane.

Hence, the correct answer is Option (B), the IUPAC name of the given compound is 2-Methyl methoxy ethane. 

This is a multiple choice answer as classified in NCERT Exemplar

(I) 3-methylphenol 

The m-cresol is an organic compound which contains a benzene ring, a -OH group and a methyl group. It has a methyl group substituted to meta position in the phenol ring. According to the IUPAC system, the -OH group is given more priority than the methyl group.

The cresols are also called hydroxytoluene or the methylphenols. These contain a benzene ring with one methyl and one phenol group substituted. There are three forms of cresols which are o-cresol, m-cresol and p-cresol. m- cresol is a colourless liquid and is viscous in nature.

In case of m-cresol, the methyl group and the hydroxyl group at 1st and 3rd position. The structure of m-cresol can be written as-

Now, if we see the IUPAC nomenclature then the -OH group should be given 1st place because it has more priority and the methyl group should be at 3rd position i.e. at meta to OH group.

Thus, the IUPAC name is- 3-Methylphenol