Organic Compounds containing Nitrogen is a quite significant topic in JEE Main Chemistry. It holds a crucial place within the broader subject area of General Organic Chemistry and about 1-2 questions get asked from the section that bear a total of around 4 marks. Thus, the complete weightage of this chapter is about 1-2% in JEE Main. If you study the theory from this chapter thoroughly, the questions are generally pretty simple to answer and score. A few of the concepts tested from Organic Compounds containing Nitrogen are - Amines, their Properties, and Reactions. Read Complete JEE Main Syllabus

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Amines: Structure, Properties and Preparation

The nitrogen is in sp3 hybridization with 3 sigma bonds and 1 lone pair of electrons for amines. Amines have tetrahedral geometry. However, the bond angle within their structure is usually lower than 109.50 as the nitrogen atom holds a lone pair of electrons that lessens the bond angle.

Classification of Amines

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Basicity of Amines

a) Aliphatic Amine

Basic Strength: NH3 < RNH2 < R2NH < R3N,

b) Aromatic Amine

Basic Strength: NH3 > Ar- NH2 > Ar2- NH2

The benzene ring lowers the electron density over the N atoms because of the resonance effect.

Preparation of Amines

Amines can be made with the use of the methods given below - 

1. Reduction of Nitro Compounds
   Reduction happens with hydrogen gas for nitro compounds when finely divided nickel, palladium or platinum is present to give amines. Also, reduction with metals in an acidic medium provides amines.
   
   

2. Ammonolysis (Hoffmann’s method)
   Ammonolysis is the process of cleavage of the C-X bond by ammonia molecule.
   
   The order of reactivity of halides with amines is given as, RI >RBr > RCl.

3. Reduction of Nitriles
   Nitriles when reduced with LiAlH4 or catalytic hydrogenation give primary amines. This method is utilized for the preparation of amines that contain one carbon atom greater than the original amine.

4. Reduction of Amides
   Amides when reduced with LiAlH4 produces amines.

5. Gabriel pthalimide synthesis
   This method is utilized to prepare primary amines. Pthalimide when reacted with ethanolic solution of KOH gives the potassium salt of phthalimide. This salt when heated with alkyl halide through alkaline hydrolysis produces the respective primary amine.

6. Hoffmann bromamide degradation reaction
   Through this method, primary amines are produced through the treatment of an amide with bromine in an aqueous or ethanolic solution of NaOH. In this degradation reaction, the migration of an alkyl or aryl group happens from the carbonyl carbon of the amide to the nitrogen atom. The amine thus produced has one carbon atom lower than the original amide.

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Reaction of Amines

1. Acylation reaction

Acylation is the process of introduction of an acyl group (R–CO–) into the molecule. The reaction is formed when a stronger base than the amine is present, like pyridine, that eliminates the HCl created and moves the equilibrium towards the product side.

2. Carbylamine reaction

When heated, aliphatic and aromatic primary amines with chloroform and ethanolic KOH, produce isocyanides or carbylamines that do not have a foul smell. Secondary and tertiary amines do not display such a reaction. This reaction has been utilized as a test for primary amines.

3. Reaction with Nitrous acid

Primary aliphatic amines when reacted with nitrous acid produce aliphatic diazonium salts. Aromatic amines when treated with nitrous acid at a low temperature give diazonium salts that can be used in the synthesis of a range of aromatic compounds. Secondary and tertiary amines are seen to react with nitrous acid in another manner.

4. Reaction with aryl sulfonyl chloride

Hinsberg’s reagent or benzenesulfonyl chloride (C6H5SO2Cl) shows reaction with primary amines and secondary amines to produce sulphonamides. Primary amine react with benzenesulfonyl chloride to give N-ethylbenzenesulphonyl amide.

With secondary amines, N,N-dimethyl-benzenesulfonamide is produced.
N, N-diethylbenzene sulphonamide does not have any H atom linked to the nitrogen atom. Therefore, it is not acidic and is thus insoluble in alkali. Tertiary amines have no reaction with benzenesulfonyl chloride. The reaction of amines with benzene sulphonyl chloride in another manner is utilized for the differentiation of primary, secondary, and tertiary amines.

5. Electrophilic substitution

Ortho- and para-positions of the -NH2 group turn into centres which have a high electron density. Thus, the -NH2 group is ortho and para directional and is also a strong activating group.

1. Bromination 

Aniline has a reaction with bromine water at room temperature to produce a white precipitate of 2, 4, 6-tribromoaniline.

2. Nitration

Nitric acid is a nitrating agent and a good oxidising agent. Therefore, the direct oxidation of aromatic amines is not beneficial because it provides tarry oxidation products along with a few nitro derivatives. In a powerful acidic medium, aniline gets protonated to give the anilinium ion that is meta directing. Hence, apart from the ortho and para derivatives, a good amount of meta derivative also gets produced.

3. Sulphonation 

Aniline when reacted with sulphuric acid gives anilinium hydrogen sulphate. This, when heated with sulphuric acid at 453-473K, produces p-aminobenzene sulfonic acid as the significant product.

6. Reactions involving displacement of Nitrogen

The diazonium group is quite a good leaving group which gets substituted by other groups like Cl-, Br-,I-,CN- and OH- that displace nitrogen from the aromatic ring. The nitrogen that gets released from the reaction mixture leaves as a gas.

7. Replacement by halide or cyanide ion

This reaction is known as the Sandmeyer reaction. Here, the nucleophiles such as Cl-,Br- and CN- can be conveniently introduced in the benzene ring when the Cu(I) ion is present.

In an alternative manner, chlorine or bromine could also be added in the benzene ring by treating the diazonium salt solution with respective halogen acid when Cu powder is present. This is known as the Gatterman reaction.

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Points to Remember for Organic Compounds containing Nitrogen 

Classification of Amines

Amines are classified according to the number of alkyl or aryl groups that are linked to the nitrogen atom. 

Classification of amines

Preparation of Amines 

• Reduction of Nitro Compounds: Here, the nitro compounds get reduced by the (H2 / Pd) reagent to form amines.

• Reduction of Nitriles: Here, the nitriles get reduced to amines by one other equally powerful reducing agent like H2 / Ni.

• Hoffmann bromamide degradation reaction: Here, the amide gets treated with bromine when an aqueous solution of NaOH is present There is a conversion of amide to a primary amine that has 1 carbon lower than the amide.

Physical Properties of Amines

• Gases that have a fishy smell are lower aliphatic amines and higher aliphatic amines are liquid.
• Lower aliphatic amines are soluble in water owing to the capacity of hydrogen bonding with the water molecules.
• Amines are soluble in organic solvents and alcohol, ether, and benzene. 
• The boiling point of amines follows an order as given below -
  Primary > Secondary> Tertiary
• The intermolecular interaction of amines is present in primary amines more than in secondary amines and such an interaction is absent with tertiary amines. 

Chemical Reactions

 a) Acylation

RNH2 + R'COCl→ R'CO NHR an N-substituted amide

R2NH + R'COCl → R'CO.NR2 an N,N disubstituted amide

b) Benzoylation (Schotten Baumann Reaction)

Primary amine has a reaction with benzoyl chloride to produce the acylated product

c) Carbylamine Reaction (Given Only by Primary Amines)

C2H5NH2 + CHCl3 + 3KOH → C2H5NC + 3KCl + 3H2O

C6H5 NH2 + CHCl3 + 3KOH → C6H5NC + 3KCl + 3H2O

d) Action with Aldehyde and Ketone

 

e) Hofmann Mustard Oil Reaction

f) Reaction with Carbonyl Chloride

C2H5 – NH2 + COCl2 → C2H5NCO + 2HCl

g) Hofmann Elimination

When a quaternary ammonium hydroxide gets strongly heated at125° or higher, it decomposes to give water, a tertiary amine and an alkene.

 h) The diazonium salts of amines

 

i) Reaction of Tertiary amines with Nitrous acid

When a tertiary aliphatic amine gets blended with nitrous acid, an equilibrium gets formed between the tertiary amine, its salt, and an N-Nitroso Ammonium compound.

j) Coupling Reactions of Arene Diazonium Salts

k) Ring Substitution in Aromatic Amines

l) Aniline -X rearrangement

These kinds of compounds are not very stable. Therefore, the group X migrates primarily at the p-position.

1. Fisher-Hepp rearrangement

2. Phenylhydroxylamine - p-aminophenol rearrangement.

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Separation of a Mixture of Amines

a) Hinsberg’s Method

Primary amine: RNH2 + C6H5SO2Cl ¾® C6H5– SO2 – NH – R + HCl 

C6H5– SO2 – NH – R : N-alkyl benzene sulfonamides

(Dissolves in NaOH because of the acidic H-attached to Nitrogen)

Secondary amine:

Tertiary amine : Tertiary amines do not have a reaction with Hinsberg’s reagent.

b) Hofmann’s Method

The mixture of amines gets treated with diethyl oxalate that forms a solid oxamide with primary amine, a liquid oxime ester with secondary amine. The tertiary amine has no reaction.

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Test for Amines

Primary amine gets treated with a strong base when chloroform is present. An isocyanide gets produced which has a very foul odour. 

Secondary amine gets converted into nitrosamine when treating the amine with nitrous acid. The resultant solutions are warmed with phenol and concentrated H2SO4. A brown or red colour gets formed first and soon, it turns blue and then green. The colour further changes to red on dilution and to greenish blue when treated with alkali.

Tertiary arylamines react with nitrous acid to produce an o-nitroso aromatic compound

Previous Year Solved Question on Amines

Question: 1 Compare the basicities of

a) H2C = CHCH2NH2, CH3CH2CH2NH2 and HC º CCH2NH2, and

b) C6H5CH2NH2, cyclohexyl – CH2NH2 and p-NO2C6H4CH2NH2.

Solution:

a The major difference between these three bases is the type of hybrid orbital utilized by Cb — the more s character it possesses, the more electron-withdrawing through induction and base weakening will it be. The HO situations are H2C = CbHCH2NH2(sp2), CH3CbH2CH2NH2(sp3), and HC º CbCH2NH2(sp). The rising order of electron–attraction is propargyl > allyl > propyl >, and the decreasing order of basicity is CH3CH2CH2NH2> H2C = CHCH2NH2 > HC º CCH2NH2

b) The decreasing order is, 

The Cb is cyclohexyl – CH2NH2 utilizes sp3 HO’s while the Cb in the benzylamines makes use of the sp2 HO’s. The electron-withdrawing p-NO2 makes the phenyl ring more electron–withdrawing and base weakening.

Question: 2 A compound X that has seven carbon atoms when treated with Br2 and KOH produces Y. Y forms carbylamine test and after diazotization and coupling with phenol forms s azodye. X is?

(A) C6H5CONH2

(B) CH­3 – (CH2)5 – CONH2

(C) CH3 –C(CH3)2- CH­2 – CH2 – CONH2

(D) O – CH3 – C6H4NH2

Solution: (A)

Question: 3 A compound (A) when reacting with PCl5 and then with NH3 gives (B), (B) when treated with Br2 and KOH gives (C). (C) when treated with NaNO2 and HCl at 0°C and the boiling with water gives o-cresol. Compound A is?

(A) o-toluic acid

(B) o-chlorotoluene

(C) o-bromo toluene

(D) m-toluic acid

Solution: (A)

Question: 4 

Solution: (D)

Question: 5

Solution: (C)

Tricks to Solve Questions from Organic Compounds containing Nitrogen 

• Questions that are from this chapter are always theory-based. It is very important that you memorize the concepts and their associated reactions thoroughly.
• Write the reactions down multiple times until you are sure that you will remember them. 
• Answer questions from inside the chapter and those given at the end of the chapter for a more intensive practice.
• Make sure to study from NCERT books to give yourself a strong launching point.
• For MCQs in which you have to identify the products or reactants, think of the whole process before you select an answer. 

Study Tips for JEE Main Chemistry 

• Build an effective study timetable for Chemistry. 
• It is essential for you to regularly read all the significant concepts and reactions as Chemistry is a huge subject area having a vast amount of theory. 
• Study from NCERT books because almost all questions from JEE Main are asked directly from them.
• Make use of additional reference books such as O.P Tandon and J.D Lee. 
• Allot more time and effort to more important chapters such as Thermodynamics, GOC, Electrochemistry, Coordination Compounds, Periodic Table, and Chemical Bonding. 
• Solve chapter-wise questions to assess your knowledge and retention. 
• Attempt as many previous years’ questions and mock tests as possible. 

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