Methods of Preparation of Haloalkanes and Haloarenes, Reactions, FAQs

Examples of Haloalkanes and Haloarenes:

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.

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 + H2SO —————–> 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.

From Hydrocarbons 

  1. From alkanes by free radical halogenation 

A complex mixture of isomeric mono- and polyhaloalkanes is formed when free radicals chlorinate or bromate alkanes, which is difficult to separate as pure compounds. As a result, the yield of any single compound is extremely low.

                                          Cl2 / UV Light

  • CH3CH2CH2CH3 ——————–> CH3CH2CH2CH2Cl + CH3CH2CHClCH3

                                               or Heat

       2. From alkenes 

  • 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.

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.

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.

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.

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.

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.

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-

  1. (CH3)2CHCH2CH2Cl, 
  2. (CH3)2CHCH(Cl)CH3
  3. (CH3)2C(Cl)CH2CH3 and 
  4. 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- 

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.

Answer:    

The above reaction gives 3-Bromocyclohexene.

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.

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.

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.

CBSE Class 12 Chemistry Syllabus Download PDF

Below is the CBSE Class 12 Syllabus along with the marking scheme and time duration of the Chemistry exam.

S.NoTitleNo. of PeriodsMarks
1Solutions107
2Electrochemistry129
3Chemical Kinetics107
4d -and f -Block Elements127
5Coordination Compounds127
6Haloalkanes and Haloarenes106
7Alcohols, Phenols and Ethers106
8Aldehydes, Ketones and Carboxylic Acids108
9Amines106
10Biomolecules127
Total70

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 ExaminationMarks
Volumetric Analysis08
Salt Analysis08
Content-Based Experiment06
Project Work and Viva04
Class record and Viva04
Total30

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.