Amines are an important class of organic compounds. They are widely found in both plants and animals. They are found among proteins, vitamins, alkaloids, hormones, etc. Synthetic examples include polymers, drugs, dyestuff, etc. These amines are widely used. For example, quinine is an important anti-malarial drug, adrenaline and ephedrine are used to raise blood pressure, Novocaine is used as an anesthetic in dentistry, codeine is used as an analgesic (as a pain reliever). Benadryl is used as an antihistamine drug. Quaternary ammonium salts are used as surfactants.
Amines are considered to be derivatives of ammonia in which one, two, or all three hydrogen atoms are replaced by an alkyl or aryl group.
Table of Contents
Classification of Amines
Amines are broken down as primary (1°), secondary (2°), or tertiary (3°) because one, two, or three hydrogens of the ammonia molecule are displaced by alkyl or aryl groups in the ammonia molecule. However, we get RNH, or ArNH2 if one hydrogen atom of ammonia is replaced by an alkyl (R) or aryl group (Ar). Nevertheless, we take R-NH-R, which is the 2° amine, if the two H atoms of the ammonia H atom of RNH are replaced by another alkyl (R) or Ar group. And the alkyl or aryl groups may be the same or different.
Displacement of all three H atoms of ammonia or the other H of R-NH-R by an alkyl (prime high) or aryl group gives Rn(prime) prime which can be 3° amines (R”) equal or unequal. R or R’).
The characteristic groups in primary, secondary, and tertiary amines are amino, imino, and tert- nitrogen.
In addition to these three types of amines, there is another class of compounds known as quaternary ammonium pounds. These compounds can be thought of as derivatives of ammonium salts in which all four H-atoms are held by alkyl or aryl groups. for example, Tetramethylammonium iodide, Tetramethylammonium Chloride, Tetra methyl ammonium bromide, etc.
Amines can be further divided into two categories:
Aliphatic Amines: Amines in which the nitrogen atom is directly bonded to one or more alkyl groups are called aliphatic amines. For example, methylamine (1°), dimethylamine (2°), and trimethylamine (3°).
Arylalkyl amines or side-chain substituted amines: Amines in which the nitrogen atom is attached to a side chain of an aromatic ring are called alkylamines. for example, Benzylamine (1°), dibenzylamine (2°) and tribenzylamine (3°).
Simple and mixed amines. Secondary and tertiary amines may be classified as simple or mixed amines according to as all the alkyl or aryl groups attached to the nitrogen atoms are the same or different. For example,
Physical Properties of Amines
Solubility: Aliphatic amines (1°, 2°, and 3°) form H-bonds with water and are therefore soluble in water. However, aromatic amines are insoluble in water due in large part to hydrocarbons.
Boiling points- The 1° amine has a higher boiling point than the 3° amine due to the presence of two H-atoms directly attached to N, resulting in a higher H-bonding in the 1° amine.
Basic Character of Amines
Aliphatic Amines
All aliphatic amines are more basic than ammonia.
In aqueous solutions, methylamine follows the basicity order (CH₂)₂NH > CH₂NH₂ > (CH₂), N (fe 2° 1 > 3º), but for ethylamine and all other higher amines, the basicity order is R₂NH > R₂N > RNH. follows. (ie 2° > 3° > 1°).
The order of basicity in the gaseous state is 3° > 2° > 1º amines.
The higher the value of Kp or the smaller the value of pKb the stronger the base.
Aromatic Amines
All aromatic amines are weaker bases than ammonia.
Electron donating groups like -CH3, – OCH3, -NH2 increase basicity while electron-withdrawing substances like -NO2, -CN, -(halogens) decrease the basicity of amine. The effect of these substances is more pronounced at p- than at m- conditions.
o-substituted anilines are weaker bases than anilines, regardless of the electron-donating or electron-withdrawing nature of the substituents. This is called the ortho effect and is caused by steric hindrance.
Aliphatic amines are more basic than aromatic amines. Like aromatic amines, the lone pair of electrons present on nitrogen participates in resonance and is therefore not available for donation, whereas it is available in aliphatic amines.
Sample Questions(FAQs)
Question 1: Give a chemical test to differentiate between ethylamine and aniline.
Answer:
Ethylamine is a primary aliphatic amine whereas aniline is a primary aromatic amine. Both can be identified by the azo dye test. When aniline is treated with HNO, (NaNO₂+ dil. HCl) at 273K, followed by treatment with an alkaline solution of 2-naphthol, the orange color is obtained, but due to the formation of ethylamine. With N2 gas gives strong effervescence of 1 alcohol.
Question 2: Give a chemical test to differentiate between aniline and N-methylamine.
Answer:
Aniline is a primary aromatic amine while N-methyl aniline is a secondary aromatic amine. The two can be separated by the carbylamine reaction. Upon mixing CHCl3 and KOH, aniline will give off an offensive odor due to the formation of phenyl carbylamine (phenyl isocyanide), while N-methyl aniline will not react.
Question 3: Why does electrophilic substitution occur more readily in aromatic amines than in benzene?
Answer:
Due to the strong activating group -NH₂, the electrons on the N-atom in aniline are denoted above the benzene ring. As a result, the electron density on the benzene ring increases as compared to benzene. Therefore, aniline becomes activated and electrophilic substitution occurs more easily in aniline.
Question 4: Give a chemical test to differentiate between aniline and benzylamine.
Answer:
Aniline and benzylamine can be separated by azo dye test. Aniline reacts with NO2 at 273-278 K to form stable benzene diazonium chloride which gives orange color on reaction with an alkaline solution of β-naphthol. Whereas benzylamine does not give this test.
Question 5: p-methoxy aniline is a stronger base than aniline but p-nitro aniline is a weaker base than amines. Explain.
Answer:
The methoxy group (-OCH3) is the electron freeing group and increases the electron density on the N atom. Therefore, it has a tendency to donate more electrons than aniline and thus is a stronger base than aniline. On the other hand, the nitro group is the electron withdrawing group and hence, the electron density on the nitrogen atom decreases. Consequently, p-nitroaniline is a weaker base than aniline.
Question 6: Can we prepare aniline by Gabriel’s phthalimide reaction?
Answer:
The Gabriel phthalimide reaction to aniline cannot be made because it requires treatment of potassium phthalimide with C6H5Cl or C6H5Br. Since aryl halides do not undergo nucleophilic substitution reactions under normal conditions, the reaction does not occur. Therefore, aniline cannot be prepared by this method.
Neeraj Anand, Param Anand
Er. Neeraj K.Anand is a freelance mentor and writer who specializes in Engineering & Science subjects. Neeraj Anand received a B.Tech degree in Electronics and Communication Engineering from N.I.T Warangal & M.Tech Post Graduation from IETE, New Delhi. He has over 30 years of teaching experience and serves as the Head of Department of ANAND CLASSES. He concentrated all his energy and experiences in academics and subsequently grew up as one of the best mentors in the country for students aspiring for success in competitive examinations.
In parallel, he started a Technical Publication "ANAND TECHNICAL PUBLISHERS" in 2002 and Educational Newspaper "NATIONAL EDUCATION NEWS" in 2014 at Jalandhar. Now he is a Director of leading publication "ANAND TECHNICAL PUBLISHERS", "ANAND CLASSES" and "NATIONAL EDUCATION NEWS".
He has published more than hundred books in the field of Physics, Mathematics, Computers and Information Technology. Besides this he has written many books to help students prepare for IIT-JEE and AIPMT entrance exams. He is an executive member of the IEEE (Institute of Electrical & Electronics Engineers. USA) and honorary member of many Indian scientific societies such as Institution of Electronics & Telecommunication Engineers, Aeronautical Society of India, Bioinformatics Institute of India, Institution of Engineers. He has got award from American Biographical Institute Board of International Research in the year 2005.
Below is the CBSE Class 12 Syllabus along with the marking scheme and time duration of the Chemistry exam.
S.No
Title
No. of Periods
Marks
1
Solutions
10
7
2
Electrochemistry
12
9
3
Chemical Kinetics
10
7
4
d -and f -Block Elements
12
7
5
Coordination Compounds
12
7
6
Haloalkanes and Haloarenes
10
6
7
Alcohols, Phenols and Ethers
10
6
8
Aldehydes, Ketones and Carboxylic Acids
10
8
9
Amines
10
6
10
Biomolecules
12
7
Total
70
CBSE Class 12 Chemistry Practical Syllabus along with Marking Scheme
The following is a breakdown of the marks for practical, project work, class records, and viva. The total number of marks for all parts is 15. The marks for both terms are provided in the table below.
Evaluation Scheme for Examination
Marks
Volumetric Analysis
08
Salt Analysis
08
Content-Based Experiment
06
Project Work and Viva
04
Class record and Viva
04
Total
30
CBSE Class 12 Chemistry Syllabus (Chapter-wise)
Unit -1: Solutions
Raoult's law.
Colligative properties - relative lowering of vapour pressure, elevation of boiling point, depression of freezing point, osmotic pressure, determination of molecular masses using colligative properties, abnormal molecular mass.
Solutions, Types of solutions, expression of concentration of solutions of solids in liquids, solubility of gases in liquids, solid solutions.
Van't Hoff factor.
Unit -2: Electrochemistry
Redox reactions, EMF of a cell, standard electrode potential
Nernst equation and its application to chemical cells
Relation between Gibbs energy change and EMF of a cell
Kohlrausch's Law
Electrolysis and law of electrolysis (elementary idea)
Dry cell-electrolytic cells and Galvanic cells
Conductance in electrolytic solutions, specific and molar conductivity, variations of conductivity with concentration.
Lead accumulator
Fuel cells
Unit -3: Chemical Kinetics
Rate of a reaction (Average and instantaneous)
Rate law and specific rate constant
Integrated rate equations and half-life (only for zerfirst-order order reactions)
Concept of collision theory (elementary idea, no mathematical treatment)
Factors affecting rate of reaction: concentration, temperature, catalyst;
Order and molecularity of a reaction
Activation energy
Arrhenius equation
Unit -4: d and f Block Elements
Lanthanoids- Electronic configuration, oxidation states, chemical reactivity and lanthanoid contraction and its consequences.
Actinoids- Electronic configuration, oxidation states and comparison with lanthanoids.
General introduction, electronic configuration, occurrence and characteristics of transition metals, general trends in properties of the first-row transition metals – metallic character, ionization enthalpy, oxidation states, ionic radii, color, catalytic property, magnetic properties, interstitial compounds, alloy formation, preparation and properties of K2Cr2O7 and KMnO4.
Unit -5: Coordination Compounds
Coordination compounds - Introduction, ligands, coordination number, color, magnetic properties and shapes
The importance of coordination compounds (in qualitative analysis, extraction of metals and biological system).
IUPAC nomenclature of mononuclear coordination compounds.
Bonding
Werner's theory, VBT, and CFT; structure and stereoisomerism
Unit -6: Haloalkanes and Haloarenes
Haloarenes: Nature of C–X bond, substitution reactions (Directive influence of halogen in monosubstituted compounds only). Uses and environmental effects of - dichloromethane, trichloro methane, tetrachloromethane, iodoform, freons, DDT.
Haloalkanes: Nomenclature, nature of C–X bond, physical and chemical properties, optical rotation mechanism of substitution reactions.
Unit -7: Alcohols, Phenols and Ethers
Phenols: Nomenclature, methods of preparation, physical and chemical properties, acidic nature of phenol, electrophilic substitution reactions, uses of phenols.
Ethers: Nomenclature, methods of preparation, physical and chemical properties, uses.
Alcohols: Nomenclature, methods of preparation, physical and chemical properties (of primary alcohols only), identification of primary, secondary and tertiary alcohols, mechanism of dehydration, and uses with special reference to methanol and ethanol.
Unit -8: Aldehydes, Ketones and Carboxylic Acids
Carboxylic Acids: Nomenclature, acidic nature, methods of preparation, physical and chemical properties; uses.
Aldehydes and Ketones: Nomenclature, nature of carbonyl group, methods of preparation, physical and chemical properties, mechanism of nucleophilic addition, the reactivity of alpha hydrogen in aldehydes, uses.
Unit -9: Amines
Diazonium salts: Preparation, chemical reactions and importance in synthetic organic chemistry.
Amines: Nomenclature, classification, structure, methods of preparation, physical and chemical properties, uses, and identification of primary, secondary and tertiary amines.
Unit -10: Biomolecules
Proteins -Elementary idea of - amino acids, peptide bond, polypeptides, proteins, structure of proteins - primary, secondary, tertiary structure and quaternary structures (qualitative idea only), denaturation of proteins; enzymes. Hormones - Elementary idea excluding structure.
Vitamins - Classification and functions.
Carbohydrates - Classification (aldoses and ketoses), monosaccharides (glucose and fructose), D-L configuration oligosaccharides (sucrose, lactose, maltose), polysaccharides (starch, cellulose, glycogen); Importance of carbohydrates.
Nucleic Acids: DNA and RNA.
The syllabus is divided into three parts: Part A, Part B, and Part C. Part A consist of Basic Concepts of Chemistry, which covers topics such as atomic structure, chemical bonding, states of matter, and thermochemistry. Part B consists of Topics in Physical Chemistry, which includes topics such as chemical kinetics, equilibrium, and electrochemistry. Part C consists of Topics in Organic Chemistry, which covers topics such as alkanes, alkenes, alkynes, and aromatic compounds.
Basic Concepts of Chemistry:
Atomic structure: This section covers the fundamental concepts of atomic structure, including the electronic configuration of atoms, the Bohr model of the atom, and the wave nature of matter.
Chemical bonding: This section covers the different types of chemical bonds, including ionic, covalent, and metallic bonds, as well as the concept of hybridization.
States of the matter: This section covers the three states of matter - solid, liquid, and gas - and the factors that influence their properties.
Thermochemistry: This section covers the principles of thermochemistry, including the laws of thermodynamics and the concept of enthalpy.
Chapters in Physical Chemistry:
Chemical kinetics: This section covers the study of the rate of chemical reactions and the factors that influence it, including the concentration of reactants, temperature, and the presence of catalysts.
Equilibrium: This section covers the principles of chemical equilibrium, including the concept of Le Chatelier's principle and the equilibrium constant.
Electrochemistry: This section covers the principles of electrochemistry, including the concept of half-cell reactions, galvanic cells, and electrolysis.
Chapters in Organic Chemistry:
Alkanes: This section covers the properties and reactions of alkanes, including their structure, isomerism, and combustion.
Alkenes: This section covers the properties and reactions of alkenes, including their structure, isomerism, and addition reactions.
Alkynes: This section covers the properties and reactions of alkynes, including their structure, isomerism, and addition reactions.
Aromatic compounds: This section covers the properties and reactions of aromatic compounds, including their structure, isomerism, and electrophilic substitution reactions.
In addition to the topics covered in the syllabus, the CBSE Class 12 Chemistry exam also tests students on their analytical and problem-solving skills, as well as their ability to apply the concepts learned in the classroom to real-world situations.
Students can also check out the Tips for the Class 12 Chemistry Exam. They can easily access the Class 12 study material in one place by visiting the CBSE Class 12 page at ANAND CLASSES (A School Of Competitions). Moreover, to get interactive lessons and study videos, download the ANAND CLASSES (A School Of Competitions) App.
Frequently Asked Questions on CBSE Class 12 Chemistry Syllabus
Q1
How many chapters are there in the CBSE Class 12 Chemistry as per the syllabus?
There are 10 chapters in the CBSE Class 12 Chemistry as per Syllabus. Students can learn all these chapters efficiently using the study materials provided at ANAND CLASSES (A School Of Competitions).
Q2
What is the marking scheme for CBSE Class 12 Chemistry practical exam according to the syllabus?
The marking scheme for CBSE Class 12 Chemistry practical exam, according to the syllabus, is 8 marks for volumetric analysis, 8 marks for salt analysis, 6 marks for the content-based experiment, 4 marks for the project and viva and 4 marks for class record and viva.
Q3
Which is the scoring chapter in Chemistry as per CBSE Class 12 syllabus?
The chapter Electrochemistry in Chemistry is the scoring chapter as per CBSE Class 12 syllabus.
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