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NCERT Class 12 Chemistry Textbook Chapter 13 With Answer PDF Free Download
Chapter 10: Amines
Amines constitute an important class of organic compounds derived by replacing one or more hydrogen atoms of ammonia molecules with an alkyl/aryl group(s).
In nature, they occur among proteins, vitamins, alkaloids, and hormones. Synthetic examples include polymers, dyestuffs, and drugs.
Two biologically active compounds, namely adrenaline, and ephedrine, both containing secondary amino groups, are used to increase blood pressure.
Novocain, a synthetic amino compound, is used as an anesthetic in dentistry. Benadryl, a well-known antihistaminic drug also contains a tertiary amino group.
Quaternary ammonium salts are used as surfactants. Diazonium salts are intermediates in the
preparation of a variety of aromatic compounds including dyes. In this Unit, you will learn about amines and diazonium salts.
I. AMINES
Amines can be considered derivatives of ammonia, obtained by the replacement of one, two, or all the three hydrogen atoms by alkyl and/or aryl groups.
In the common system, an aliphatic amine is named by prefixing the alkyl group to amine, i.e., alkylamine as one word (e.g., methylamine).
In secondary and tertiary amines, when two or more groups are the same, the prefix di or tri is appended before the name of the alkyl group.
In the IUPAC system, amines are named as alkanamines, derived by the replacement of ‘e’ of alkane by the word amine. For example, CH3NH2 is named methenamine.
In case, more than one amino group is present at different positions in the parent chain, their positions are specified by giving numbers to the carbon atoms bearing –NH2 groups, and suitable prefix such as di, tri, etc. is attached to the amine.
The letter ‘e’ of the suffix of the hydrocarbon part is retained. For example, H2N–CH2–CH2–NH2 is named ethane-1, 2-diamine.
The lower aliphatic amines are gases with a fishy odor. Primary amines with three or more carbon atoms are liquid and still higher ones are solid.
Aniline and other arylamines are usually colorless but get colored on storage due to atmospheric oxidation.
Lower aliphatic amines are soluble in water because they can form hydrogen bonds with water molecules.
However, solubility decreases with an increase in the molar mass of amines due to an increase in the size of the hydrophobic alkyl part.
Higher amines are essentially insoluble in water. Considering the electronegativity of nitrogen of amine and oxygen of alcohol at 3.0 and 3.5 respectively, you can predict the pattern of solubility of amines and alcohols in water.
Out of butan-1-ol and butan-1-amine, which will be more soluble in water and why?
Amines are soluble in organic solvents like alcohol, ether, and benzene. You may remember that alcohols are more polar than amines and form stronger intermolecular hydrogen bonds than amines.
| Author | NCERT |
| Language | English |
| No. of Pages | 22 |
| PDF Size | 1.1 MB |
| Category | Chemistry |
| Source/Credits | ncert.nic.in |
NCERT Solutions Class 12 Chemistry Chapter 13 Amines
Q . 13.1 :
Write IUPAC names of the following compounds and classify them into primary, secondary, and tertiary amines.
(i) ( CH3 )2 CH NH 2
(ii) CH3 ( CH2 )2 NH 2
(iii) CH3 NH CH ( CH3 )2
(iv) ( CH3 )3 CNH 2
(v) C6 H5 NH CH 3
(vi) ( CH3 CH2 )2 N CH3
(vii) m – Br C6 H4 NH2
Solution :
(i) 1 – Methylethanamine ( 10 amine )
(ii) Propan – 1 – amine ( 10 amine )
(iii) N – Methyl – 2 – methyl ethanamine ( 20 amine )
(iv) 2 – Methylpropan – 2 – amine ( 10 amine )
(v) N – Methyl benzamine or N – methylaniline ( 20 amine )
(vi) N – Ethyl – N – methyl ethanamine ( 30 amine )
(vii) 3 – Bromobenzenamine or 3 – bromoaniline ( 10 amine )
Q . 13.2 :
Give one chemical test to distinguish between the following pairs of compounds.
(i) Methylamine and dimethylamine (ii) Secondary and tertiary amines
(iii) Ethylamine and aniline (iv) Aniline and benzylamine
(v) Aniline and N-methylaniline.
Solution :
(i) dimethylamine & Methylamine can be made notable by the carbylamine test.
Carbylamine test: foul-smelling isocyanides or carbylamines are formed when Aliphatic & aromatic primary amines are heated with chloroform & ethanol potassium hydroxide.
Methylamine (being an aliphatic primary amine) gives a positive carbylamine test, but dimethylamine does not.
(ii) Tertiary amines & Secondary can be made notable by allowing them to react with Hinsberg’s reagent ( benzene sulphonyl chloride, C6 H5 SO2 Cl ).
A product which is insoluble in alkali is formed when Secondary amines react with Hinsberg’s reagent to form a product that is insoluble in alkali a For example, N, N – diethyl amine reacts with Hinsberg’s reagent to form N, N – diethyl benzene sulphonamide, which is insoluble in an alkali. Tertiary amines, however, do not react with Hinsberg’s reagent.
(iii) azo – dye test can distinguish aniline & Ethylamine.
When aromatic amines are made to react with HNO 2 ( NaNO 2 + dil. HCl ) at 0 – 5 ° C, A dye is obtained which is followed by making it react with the alkaline solution of 2 – naphthol. The dye is observed to be in the following colours: yellow, red, or orange in colour. A brisk effervescence is given out by Aliphatic amines due to the evolution of N2 gas under analogous conditions.
(iv) benzylamine & Aniline can be made notable by reacting them with nitrous acid, which is made ready in situ from a sodium nitrite & mineral acid. Unstable diazonium salt is formed when nitrous acid reacts with Benzylamine, which gives a by – product as alcohol along with the evolution of N2 gas
In another case, HNO 2 reacts with aniline at a very low temperature which in turn forms stable diazonium salt. Hence, the evolution of nitrogen gas does not happen.
(v) N – methylaniline & Aniline can be made notable by using the Carbylamine test.
On heating Primary amines with ethanolic, chloroform, and potassium hydroxide, foul-smelling isocyanides or carbylamines are formed. As Aniline is a primary aromatic primary, it gives a positive carbylamines test. On the other h&, as, N – methyl aniline is a secondary amine it does not give a positive carbylamines test.
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