Alkyl halide (haloalkane) and aryl halide (haloarene) are formed when hydrogen atoms in an aliphatic or aromatic hydrocarbon are replaced by halogen atoms. Haloalkanes have halogen atom(s) attached to an alkyl group’s sp3 hybridized carbon atom(s), whereas haloarenes have halogen atom(s) attached to an aryl group’s sp2 hybridized carbon atom(s). Many halogen-containing organic compounds exist in nature, and some of them have clinical applications.
Table of Contents
Examples of Haloalkanes and Haloarenes:
Methods of Preparation of Haloalkanes
There are various methods to prepare haloalkanes. Haloalkanes can be prepared from alcohol, from hydrocarbons. Let’s take a look at all the methods,
From Alcohol
When alcohol reacts with concentrated halogen acids, phosphorus halides, or thionyl chloride, the hydroxyl group is replaced by halogen. Thionyl chloride is preferred because alkyl halide is formed in this reaction along with the gases SO2 and HCl. Because the two gaseous products are escapable, the reaction yields pure alkyl halides. The presence of a catalyst, ZnCl2, is required for the reactions of primary and secondary alcohols with HCl. (R – Alkyl group)
ZnCl2
R-OH + HCl —————–> R-Cl + H2O
R-OH + PCl3 —————> R-Cl + POCl3 + HCl
R-OH + NaBr + H2SO4 —————–> R-Br + NaHSO4 + H2O
3R-OH + PX3 —————> 3R-X + H3PO3 (X = Cl, Br)
red P/X2
R-OH —————> R-X
X2 = Br2, I2
R-OH + SOCl2 —————> R-Cl + SO2 + HCl
Alkyl chloride is produced by either passing dry hydrogen chloride gas through an alcohol solution or heating an alcohol-concentrated aqueous halogen acid mixture.
Addition of hydrogen halides: A reaction with hydrogen chloride, hydrogen bromide, or hydrogen iodide converts an alkene to the corresponding alkyl halide.
(CH3)2C=C(CH3)2 + HX —————–> (CH3)2C-CX(CH3)2
Propene yields two products:
CH3CH=CH2 + H-I ——————–> CH3CH2CH2I + CH3CHICH3
(Minor) (Major)
Addition of halogens
In the laboratory, adding bromine in CCl4 to an alkene results in the release of a reddish-brown color of bromine, which is an important method for detecting a double bond in a molecule. The reaction results in the formation of colorless vic-dibromides.
CCl4
CH2=CH2 + Br2 ————————> BrCH2-CH2Br
(vic-Dibromides)
Halogen Exchange
Alkyl iodides are frequently synthesized by reacting alkyl chlorides/bromides with NaI in dry acetone. This reaction is also known as the Finkelstein reaction.
R-X + NaI ————–> R-I + NaX (X = Cl, Br)
Heat an alkyl chloride/bromide in the presence of a metallic fluoride to produce alkyl fluorides. such as AgF (silver fluoride), Hg2F2, CoF2, or SbF3. Swarts reaction is the name given to this reaction.
H3C-Br + AgF ————–> H3C-F + AgBr
Method of Preparation of Haloarenes
Haloarenes can be prepared by various means, for instance, they can be prepared from hydrocarbons, amines. Let’s take a look at these methods in detail,
From hydrocarbons
Aryl chlorides and bromides can be easily synthesized by electrophilic substitution of arenes with chlorine or bromine in the presence of Lewis acid catalysts such as iron or iron(III) chloride.
Because of the large difference in melting points, the ortho and para isomers can be easily separated.
From amines
From amines, haloarenes are made using Sandmeyer’s reaction. When an aromatic amine is dissolved in the solution of sodium nitrite then, a diazonium salt is formed. Freshly prepared diazonium salt is mixed with cuprous chloride or cuprous bromide, the diazonium group is replaced by the –Cl or –Br group.
The presence of cuprous halide is not required for iodine replacement of the diazonium group, which can be accomplished simply by shaking the diazonium salt with potassium iodide.
Conceptual questions
Question 1: Why isn’t sulphuric acid used in the alcohol-KI reaction?
Answer :
We know that (H2SO4) sulfuric acid is an oxidizing agent, if we use it in an alcoholic KI reaction, it will convert KI to corresponding HI and oxidize the HI. That’s why sulfuric acid can not be used in the reaction of alcohols with KI.
Question 2: Identify all of the monochloro structural isomers that are likely to be formed during free radical monochlorination of (CH3)2CHCH2CH3.
Answer :
When the monochlorination occurs the following 4 product will produce-
(CH3)2CHCH2CH2Cl,
(CH3)2CHCH(Cl)CH3,
(CH3)2C(Cl)CH2CH3 and
CH3CH(CH2Cl)CH2CH3.
Question 3: How to distinguish between C2H5Br and C6H5Br give chemical reaction test.
Answer :
Aqueous NaOH is used to heat both. C2H5Br produces ethanol and NaBr, which when combined with AgNO3 produces a yellow precipitate of AgBr. This test yields no results for C6H5Br.
Question 4: What will be the major product when cyclohexene react with bromine in presence of heat-
Answer:
The above reaction gives 3-Bromocyclohexene.
Question 5: Why do haloalkanes dissolve so easily in organic solvents?
Answer:
Because the new forces of attraction formed between haloalkanes and solvent molecules are as strong as the forces of attraction that are being broken.
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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