Grade 11
  1. Basic concepts of chemistry  1.1. Importance of Chemistry  1.2. Nature and scope of chemistry  1.3. laws of chemical combination  1.3.1. Law of conservation of mass  1.3.2. Law of definite proportions  1.3.3. Law of multiple proportions  1.3.4. Law of gaseous volume  1.3.5. Avogadro's Law  1.4. Dalton's atomic theory  1.5. Mole concept and molar mass  1.6. Percent composition  1.7. Empirical and molecular formula  1.8. Stoichiometry and Stoichiometric Calculations  1.9. Limiting reagent concept
  2. Structure of the atom  2.1. Discovery of the electron, proton, and neutron  2.2. Atomic Model  2.2.1. Thomson's model  2.2.2. Rutherford's model  2.2.3. Bohr's model  2.3. Quantum mechanical model of the atom  2.4. Dual nature of matter and radiation  2.5. Heisenberg's uncertainty principle  2.6. Quantum numbers  2.7. Atomic orbitals and their shapes  2.8. Electronic configuration of elements  2.9. Aufbau principle  2.10. Pauli's exclusion principle  2.11. Hund's maximum multiplicity rule  2.12. de Broglie's hypothesis  2.13. Photoelectric effect
  3. Classification of elements and periodicity in properties  3.1. Historical development of the periodic table  3.2. Modern Periodic Law and Periodic Table  3.3. Periodic trends in properties  3.3.1. Atomic and Ionic Radius  3.3.2. Ionization enthalpy  3.3.3. Electron gain enthalpy  3.3.4. Electronegativity  3.3.5. Valency  3.3.6. Metallic and Non-Metallic Properties  3.3.7. Oxidation states  3.4. Unusual Properties of the First Elements
  4. Chemical Bonding and Molecular Structure  4.1. Kossel–Lewis approach to chemical bonding  4.2. Ionic or electrovalent bond  4.3. Covalent bond and its features  4.4. Bond parameters  4.5. VSEPR Theory  4.6. Valence bond theory  4.7. Hybridization and its types  4.8. Molecular orbital theory  4.8.1. Bond order and stability  4.9. Hydrogen bonding
  5. States of matter  5.1. Intermolecular forces  5.2. Gas Laws  5.2.1. Boyle's law  5.2.2. Charles's Law  5.2.3. Avogadro's Law  5.2.4. Dalton's law of partial pressure  5.2.5. Graham's law of spread  5.3. Ideal Gas Equation and Applications  5.4. Real gases and deviations from ideal behaviour  5.5. Kinetic molecular theory of gases  5.6. Liquefaction of gases  5.7. Properties of Liquids  5.8. Surface tension and viscosity
  6. Thermodynamics  6.1. System and environment  6.2. Types of systems in thermodynamics  6.3. Types of procedures  6.4. First law of thermodynamics  6.5. Internal energy and enthalpy  6.6. Heat capacity and specific heat  6.7. Hess's law of constant heat summation  6.8. Bond dissociation enthalpy  6.9. Enthalpy of formation and combustion  6.10. Enthalpy of solution and neutralization  6.11. Spontaneity and the second law of thermodynamics  6.12. Gibbs free energy and its applications
  7. Balance  7.1. The concept of balance  7.2. Equilibrium constant and its applications  7.3. Le Chatelier's principle  7.4. Ionic equilibrium in solutions  7.5. Acid and Base Theory  7.5.1. Arrhenius concept  7.5.2. Bronsted-Lowry concept  7.5.3. Lewis concept  7.6. pH Scale and pOH  7.7. Common ion effect  7.8. Hydrolysis of salts  7.9. Buffer solutions and their mechanism of action  7.10. Solubility equilibrium of sparingly soluble salts
  8. Redox reactions  8.1. Oxidation and reduction concepts  8.2. Oxidation number and its applications  8.3. Redox reactions in terms of electron transfer  8.4. Balancing redox reactions (oxidation number and ion-electron methods)  8.5. Types of redox reactions  8.6. Electrochemical Cells and Redox Reactions
  9. Hydrogen  9.1. Position of Hydrogen in the Periodic Table  9.2. Isotopes of hydrogen  9.3. Preparation of Hydrogen  9.4. Properties of Hydrogen  9.5. Hydrides and their classification  9.6. Water and heavy water  9.7. Hydrogen peroxide and its properties  9.8. Uses of Hydrogen and Its Compounds
  10. S-block elements (alkali and alkaline earth metals)  10.1. Group 1 Elements - Properties and Trends  10.2. Group 2 Elements - Properties and Trends  10.3. Unusual properties of lithium and beryllium  10.4. Important compounds of sodium and their uses  10.5. Important Compounds of Magnesium and Calcium
  11. Some p-block elements  11.1. General Introduction to p-Block Elements  11.2. Group 13 Elements  11.2.1. Boron and its compounds  11.3. Group 14 Elements  11.3.1. Carbon and its allotropes  11.3.2. Important Compounds of Carbon and Silicon
  12. Organic Chemistry - Some Basic Principles and Techniques  12.1. Classification and Nomenclature of Organic Compounds  12.2. Structural representation of organic compounds  12.3. Classification of organic reactions  12.4. Electronic Effects in Organic Chemistry  12.4.1. Inductive effect  12.4.2. Resonance effect  12.4.3. Hyperconjugation  12.5. Reaction mechanism and intermediate species  12.6. Purification and qualitative analysis of organic compounds
  13. Hydrocarbons  13.1. Hydrocarbons  13.1.1. Preparation and Properties of Alkenes  13.2. alkene  13.2.1. Preparation and Properties of Alkenes  13.2.2. Electrophilic addition reactions  13.3. Alkynes  13.3.1. Preparation and Properties of Alkynes  13.4. Aromatic hydrocarbons  13.4.1. Structure and properties of benzene  13.4.2. Electrophilic substitution reactions of benzene
  14. Environmental Chemistry  14.1. Environmental Pollution  14.2. Atmospheric pollution and the greenhouse effect  14.3. Water pollution and treatment methods  14.4. Soil pollution and its effects  14.5. Industrial waste and its treatment  14.6. Strategies for pollution control

Grade 11 → Hydrocarbons → alkene ↓


Electrophilic addition reactions


Electrophilic addition reactions are a class of reactions in organic chemistry where an electrophile, which is a species that is attracted to electrons, reacts with a nucleophile, which is a species that donates an electron pair. These reactions are specific to alkenes. Alkenes are hydrocarbons that contain at least one carbon–carbon double bond. The presence of this double bond causes alkenes to be more reactive than alkenes in many reactions, especially electrophilic addition reactions.

Nature of the double bond

In alkenes, the carbon-carbon double bond consists of a sigma (σ) bond and a pi (π) bond. The sigma bond is formed due to the head-on overlapping of atomic orbitals, while the pi bond is formed due to the side-by-side overlap of pi orbitals. The pi bond is usually weaker than the sigma bond and is easily broken in chemical reactions.

C = C
,
haha

The electrons in the pi bond are essentially exposed and prone to being attacked by an electrophile. An electrophile usually has a positive charge or electron-deficient site. During an electrophilic addition reaction, the electrophile will be attracted to the electron-rich pi bond of the alkene.

General mechanism of electrophilic addition reactions

The mechanism of an electrophilic addition reaction generally involves the following steps:

  1. Formation of carbocation: The first step is the attack of the alkene on the electrophile. The pi electrons form a new bond with the electrophile, resulting in a positively charged intermediate known as a carbocation.
  2. Attack by a nucleophile: Once the carbocation is formed, it is attacked by a nucleophile, completing the addition and forming the final product.
c = c + e step 1 C–C–E

where E represents the electrophile that attacks the double bond.

Markovnikov's law

Markovnikov's rule is an important principle that helps predict the outcome of electrophilic addition reactions for asymmetric alkenes. According to this rule, in the addition of HX (where X is a halogen) to an asymmetric alkane, the hydrogen atom will attach to the carbon with the greater number of hydrogen atoms, and the halogen will attach to the carbon with the fewer number of hydrogen atoms. In other words, "the rich get richer".

CH3-CH=CH2 + HCl → CH3-CHCl-CH3

In the example above, propane (CH3-CH=CH2) reacts with hydrogen chloride (HCl). The H from HCl attaches to the terminal carbon with more hydrogen, and the Cl attaches to the carbon with fewer hydrogens.

Examples of electrophilic addition reactions

1. Addition of hydrogen halides

Hydrogen halides such as hydrogen chloride (HCl), hydrogen bromide (HBr) and hydrogen iodide (HI) readily add to alkanes. Let us consider the addition of HBr:

HBR C = C CC-BR

This reaction follows the process discussed earlier, with the pi electrons attacking hydrogen, forming a carbocation, which is then attacked by the bromide ions.

2. Addition of water (hydration)

The addition of water to an alkene is called hydration and usually requires an acid catalyst such as sulfuric acid. This reaction usually proceeds with the formation of an alcohol.

CH2=CH2 + H2O → CH3-CH2OH

Ethene reacts with water in the presence of acid to form ethanol.

3. Halogenation

Halogens such as chlorine (Cl2) and bromine (Br2) can add to the alkene double bond. Let us consider below the addition of bromine to ethene, resulting in the formation of a dibromo compound:

C=C BR2 CC-BR2

In this mechanism, the alkene attacks one of the bromine atoms, resulting in the formation of a bromonium ion, which is then attacked by the bromide ion.

Effect of substituents on electrophilic addition

The presence of different substituents on the alkene can affect the rate and orientation of the electrophilic addition reaction. Electron-releasing groups (such as alkyl groups) stabilize the carbocation intermediate by hyperconjugation and the inductive effect, thus speeding up the reaction. Conversely, electron-withdrawing groups will destabilize the carbocation, slowing down the reaction.

Conclusion

Electrophilic addition reactions are important in organic synthesis and provide a means of transforming simple alkenes into more complex compounds. The ability to predict the orientation and outcome of these reactions using concepts such as Markovnikov's rule allows chemists to design synthetic routes to a wide range of organic products. Understanding these reactions is fundamental to further study and development of chemical compounds in organic chemistry.


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Preparation and Properties of Alkenes
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Electrophilic addition reactions

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