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 → Alkynes ↓


Preparation and Properties of Alkynes


Alkynes are an important group of organic compounds characterized by the presence of at least one carbon-carbon triple bond. They have the general formula C n H 2n-2, where n is the number of carbon atoms. Alkynes are unsaturated hydrocarbons and are known for their reactivity due to the triple bond. In this lesson, we will explore the preparation methods and properties of alkynes in detail.

Preparation of alkynes

1. Dehydrohalogenation of dihalides

Alkynes can be prepared by dehydrohalogenation of 1,2-dihalides. For example, consider the synthesis of ethene (commonly known as acetylene):

CH 2 CHBr + KOH ⟶ CH≡CH + KBr + H 2 O

In this reaction, the dihalide is reacted with an alcoholic solution of potassium hydroxide to remove one molecule of hydrogen halide, forming an alkyne.

Visual example:

H BR C C BR + KOH H H

2. Hydrolysis of calcium carbide

Another method of preparing ethyne is by the hydrolysis of calcium carbide:

CaC 2 + 2 H 2 O ⟶ C 2 H 2 + Ca(OH) 2

In this laboratory method, calcium carbide is reacted with water to form ethyne and calcium hydroxide.

Visual example:

CAC 2 + 2H 2 O C 2 H 2 + Ca(OH) 2

3. Alkylation of terminal alkynes

Terminal alkynes can be alkylated using a strong base and an alkyl halide. This process increases the length of the carbon chain:

HC≡CH + NaNH 2 + RX ⟶ HC≡CR + NaX + NH 3

A terminal alkyne reacts with a strong base such as sodium amide to yield an alkyne ion, which can react with an alkyl halide to form a long-chain alkyne.

Properties of alkynes

1. Physical properties

Boiling and melting point

The boiling and melting points of alkynes increase with molecular weight. However, the boiling point of alkynes is slightly higher than that of alkenes and alkenes of the same molecular weight because of better packing due to the linear structure.

Butyne (C 4 H 6 ) boiling point ≈ 9.5°C Octyne (C 8 H 14 ) boiling point ≈ 125°C

Solubility

Alkynes are generally insoluble in water due to their nonpolar nature, but are soluble in nonpolar solvents like benzene, ether, and acetone.

2. Chemical properties

Acidity of terminal alkynes

Terminal alkynes have a slightly acidic hydrogen atom at the terminal carbon, which is due to the s-character of the sp-hybridized carbon:

HC≡CH + NaNH 2 ⟶ HC≡C⁻ Na⁺ + NH 3

Hydrogen can be removed by strong bases such as sodium amide to form acetylide ions.

Addition reactions

Due to the presence of multiple bonds, alkynes undergo addition reactions similar to alkenes:

CH≡CH + H 2 ⟶ CH 2 CH 2 (Ethene) CH≡CH + 2H 2 ⟶ CH 3 CH 3 (Ethane)

In these reactions, hydrogen adds across the triple bond to convert the alkyne to an alkene or alkane.

Halogenation

When treated with halogens, alkynes form dihalides and tetrahalides:

CH≡CH + Cl 2 ⟶ CHCl=CHCl (1,2-Dichloroethene) CH≡CH + 2Cl 2 ⟶ CCl 2 HCCl 2 (Tetrachloroethane)

Visual example:

C C + Cl 2 CHCl=CHCl

Alkynes offer a wide variety of reactions and methods of synthesis, highlighting their importance in synthetic organic chemistry. Understanding the properties and preparation of these compounds provides a foundation for delving deeper into more complex chemical reactions and applications.

This detailed information about the preparation and properties of alkynes is important for understanding their role and utility in chemistry and industrial applications. By mastering the basic principles explained in this guide, you lay a strong foundation for exploring advanced organic synthesis and processes involving alkynes.


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Preparation and Properties of Alkynes

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