Amines are organic compounds that contain a nitrogen atom bonded to one or more alkyl or aryl groups. They can be classified as primary, secondary, or tertiary, depending on the number of alkyl or aryl groups attached to the nitrogen atom.

Amines have a basic character due to the presence of a lone pair of electrons on the nitrogen atom, which can accept a proton (H+) to form a positively charged ammonium ion. The basicity of amines depends on the electronic and steric effects of the substituents attached to the nitrogen atom. Amines can be prepared by various methods, such as reduction of nitro compounds, Gabriel phthalimide synthesis, reduction of nitriles, and nucleophilic substitution reactions. We are going to discuss on Class 12 Amines NCERT Solution here.


Class 12 Amines NCERT Solutions


Here are the NCERT solutions for some of the questions related to amines from the class 12 chemistry textbook:


Question : Classify the following amines as primary, secondary and tertiary amines:

(i) CH3NH2

(ii) (CH3)2NH

(iii) (CH3)3N

(iv) C6H5NH2


Answer:

(i) CH3NH2 - Primary amine

(ii) (CH3)2NH - Secondary amine

(iii) (CH3)3N - Tertiary amine

(iv) C6H5NH2 - Primary amine


Question : Write the equations for the preparation of the following compounds from aniline:

(i) Chlorobenzene

(ii) p-nitroaniline

(iii) Benzyl alcohol


Answer:

(i) Chlorobenzene:

C6H5NH2 + HCl → C6H5NH3+Cl-

C6H5NH3+Cl- + NaOH → C6H5Cl + NaCl + H2O


(ii) p-nitroaniline:

C6H5NH2 + HNO3 → C6H5NO2 + H2O

C6H5NO2 + Sn/HCl → p-nitroaniline + H2O + SnCl2


(iii) Benzyl alcohol:

C6H5NH2 + HNO3 → C6H5NO2 + H2O

C6H5NO2 + H2O → C6H5OH + HNO3


Question : What is the difference between a primary amine, a secondary amine and a tertiary amine?

Answer: Primary amines have one alkyl or aryl group attached to the nitrogen atom, while secondary amines have two alkyl or aryl groups attached to the nitrogen atom, and tertiary amines have three alkyl or aryl groups attached to the nitrogen atom.


Question : Explain why aniline is a weaker base than methylamine?

Answer: Aniline is a weaker base than methylamine because the lone pair of electrons on the nitrogen atom in aniline is involved in resonance with the benzene ring. Due to resonance, the lone pair of electrons is delocalized over the benzene ring, making it less available for donation to a proton. This reduces the basicity of aniline.


On the other hand, in methylamine, the lone pair of electrons on the nitrogen atom is not involved in any resonance. Hence, the lone pair is more available for donation to a proton, making it a stronger base than aniline.


Question : Explain why aliphatic primary amines are stronger bases than ammonia?

Answer: Aliphatic primary amines are stronger bases than ammonia because they have an alkyl group attached to the nitrogen atom. The alkyl group is an electron-donating group that increases the electron density on the nitrogen atom, making it more available for donation to a proton. The electron-donating nature of the alkyl group also destabilizes the ammonium ion formed after protonation, making the transfer of a proton more favorable. Hence, aliphatic primary amines are stronger bases than ammonia.


Question : Explain why aromatic amines are weaker bases than aliphatic amines?

Answer: Aromatic amines are weaker bases than aliphatic amines because the lone pair of electrons on the nitrogen atom is involved in resonance with the aromatic ring. This delocalizes the lone pair of electrons over a larger area and reduces its availability for donation to a proton. In contrast, aliphatic amines do not have this resonance stabilization, and hence their lone pair of electrons is more available for donation to a proton.


Question : Write the equation for the preparation of ethanamine from ethanenitrile?

Answer: Ethanamine can be prepared from ethanenitrile by reducing it using LiAlH4 or NaBH4 followed by hydrolysis. The equation for the preparation of ethanamine from ethanenitrile is:


CH3CN + 4[H] → CH3CH2NH2

(CH3CH2NH2 can also be written as C2H5NH2)


Note: [H] represents the reducing agent (LiAlH4 or NaBH4).


Question : Write the structure of the following compounds:

(i) N-methylethanamine

(ii) N,N-dimethylbutan-1-amine

(iii) N-phenylethanamine


Answer:

(i) N-methylethanamine: CH3-NH-CH2-CH3

(ii) N,N-dimethylbutan-1-amine: CH3-N(CH3)-CH2-CH2-CH(CH3)-CH3

(iii) N-phenylethanamine: C6H5-NH-CH2-CH3


Question : What is meant by the term basicity of amines?

Answer: The basicity of amines refers to their ability to accept a proton (H+) from an acid. Amines act as bases because the nitrogen atom has a lone pair of electrons that can accept a proton. The basicity of amines depends on the availability of the lone pair of electrons on the nitrogen atom, which is influenced by factors such as the nature of the substituents attached to the nitrogen atom and the electronic and steric effects of these substituents.



These are some of the NCERT solutions for questions related to amines from the class 12 chemistry textbook. Amines NCERT solutions