Undergraduate
  1. General chemistry  1.1. Introduction to Chemistry  1.2. Atomic Structure  1.2.1. Subatomic particles  1.2.2. Atomic Model  1.2.3. Quantum numbers  1.2.4. Electron Configuration  1.2.5. Periodic trends  1.2.6. Isotopes and their applications  1.3. Chemical bond  1.3.1. Ionic bond  1.3.2. Covalent bonds  1.3.3. Metal Bond  1.3.4. Hybridization  1.3.5. Molecular geometry and VSEPR theory  1.3.6. Bond polarity and dipole moment  1.4. Stoichiometry  1.4.1. Mole concept  1.4.2. Empirical and molecular formula  1.4.3. Limiting reactant and excess reactant  1.4.4. Percent Yield and Purity  1.4.5. Dilution calculation  1.5. States of matter  1.5.1. Gas Laws  1.5.2. Matter and Intermolecular Forces  1.5.3. Solid and Crystal Structures  1.5.4. Phase diagram  1.5.5. Plasma and supercritical fluid  1.6. Chemical reactions  1.6.1. Types of Chemical Reactions  1.6.2. Balancing Chemical Equations  1.6.3. Thermochemical reactions  1.6.4. Reaction energy profiles  1.7. Solutions and Mixtures  1.7.1. Concentration units  1.7.2. Syndrome properties  1.7.3. Solubility and Solubility Rules  1.7.4. Henry's Law and Raoult's Law  1.7.5. Partition coefficient  1.8. Chemical equilibrium  1.8.1. Law of mass action  1.8.2. Le Chatelier's principle  1.8.3. Reaction quotient  1.8.4. To use this online calculator for Equilibrium Constant, enter Equilibrium Constant (Eq.) and hit the calculate button. Here is how the Equilibrium Constant calculation can be explained with given input values -> 0.05 = 0.05/0.  1.8.5. Acid-base balance  1.9. Acids and bases  1.9.1. Arrhenius, Brønsted–Lowry, and Lewis definitions  1.9.2. pH and pOH  1.9.3. Acid-base titration  1.9.4. Buffer Solution  1.9.5. Acid-base indicator  1.9.6. Polyprotic Acids and Bases  1.10. Electrochemistry  1.10.1. redox reactions  1.10.2. Galvanic and Electrolytic Cells  1.10.3. Nernst equation  1.10.4. Electrolysis  1.10.5. Faraday's laws of electrolysis  1.11. Thermodynamics  1.11.1. Laws of Thermodynamics  1.11.2. Enthalpy, entropy and Gibbs free energy  1.11.3. Spontaneity of reactions  1.11.4. Thermodynamic cycles (Hess's law, Carnot cycle)  1.12. Kinetics  1.12.1. Rate law and reaction order  1.12.2. Activation Energy and Catalyst  1.12.3. Collision theory  1.12.4. Reaction mechanism  1.12.5. Transition state theory
  2. Organic chemistry  2.1. Structure and relationships  2.1.1. Hybridisation in Carbon Compounds  2.1.2. Resonance and aromatization  2.1.3. Molecular orbitals  2.1.4. Inductive and mesomeric effects  2.2. Hydrocarbons  2.2.1. Hydrocarbons  2.2.2. Alkene  2.2.3. Alkynes  2.2.4. Aromatic compounds  2.2.5. Cycloalkanes and Conformation  2.3. Functional Group  2.3.1. Alcohols and phenols  2.3.2. Ethers and epoxides  2.3.3. Aldehyde and ketone  2.3.4. Carboxylic acids and derivatives  2.3.5. Amin  2.3.6. Esters and amides  2.3.7. Thiols and sulfides  2.4. Stereoscopic  2.4.1. Isomerism in Stereochemistry  2.4.2. Chirality and optical activity  2.4.3. Structural analysis  2.4.4. Diastereomers and Enantiomers  2.5.1. Substitution reactions  2.5.2. Elimination reactions  2.5.3. Addition reactions  2.5.4. Radical reactions  2.5.5. Rearrangement reactions  2.5.6. Pericyclic Reactions  2.6. Spectroscopy and structural analysis  2.6.1. Infrared Spectroscopy  2.6.2. Nuclear magnetic resonance spectroscopy  2.6.3. Mass Spectrometry  2.6.4. UV-visible spectroscopy  2.6.5. X-ray crystallography  2.7. Polymer chemistry  2.7.1. Addition and Condensation Polymers  2.7.2. Polymerization mechanism  2.7.3. Biodegradable Polymer  2.7.4. Conducting and smart polymers
  3. Inorganic chemistry  3.1. Coordination chemistry  3.1.1. Ligands and coordination compounds  3.1.2. Crystal field theory  3.1.3. Molecular Orbital Theory in Coordination Compounds  3.1.4. Jahn–Taylor distortion  3.2. Main Group Chemistry  3.2.1. Alkali and alkaline earth metals  3.2.2. Halogens and Noble Gases  3.2.3. Transition metals and their complexes  3.2.4. Lanthanides and Actinides  3.3. Solid state chemistry  3.3.1. Crystal lattices and unit cells  3.3.2. Defects in solids  3.3.3. Electrical and magnetic properties  3.3.4. Superconductivity  3.4. Bio-inorganic chemistry  3.4.1. Metal ions in biology  3.4.2. Enzymatic reactions with metals  3.4.3. Metal poisoning and detoxification  3.4.4. Metalloproteins and Metalloenzymes
  4. Physical chemistry  4.1. Quantum Chemistry  4.1.1. Wave–particle duality  4.1.2. Schrödinger Equation  4.1.3. Quantum Numbers and Orbitals  4.1.4. Atomic and molecular spectroscopy  4.2. Statistical mechanics  4.2.1. Maxwell–Boltzmann distribution  4.2.2. Partitioning functions  4.2.3. Bose–Einstein and Fermi–Dirac statistics  4.3. Chemical thermodynamics  4.3.1. Gibbs Free Energy  4.3.2. Phase transition  4.3.3. Thermodynamic efficiency  4.4. Surface chemistry  4.4.1. Absorption and Catalysis  4.4.2. Colloids and Emulsions
  5. Analytical Chemistry  5.1. Classical methods  5.1.1. Gravimetric Analysis  5.1.2. titrimeter  5.2. Instrumental methods  5.2.1. Chromatography  5.2.2. Spectroscopy  5.2.3. Electroanalytical methods  5.2.4. X-ray diffraction
  6. Industrial Chemistry  6.1. Petrochemistry  6.2. Chemical engineering principles  6.3. Green Chemistry  6.4. Pharmaceuticals and Drug Synthesis
  7. Biochemistry  7.1. Carbohydrates  7.2. Proteins and enzymes  7.3. Lipids and membranes  7.4. Nucleic acids  7.5. Metabolism and Bioenergetics  7.6. Enzyme kinetics and mechanism

Undergraduate → Organic chemistry → Hydrocarbons ↓


Alkynes


Alkynes are an important class of hydrocarbons in organic chemistry. These molecules are composed entirely of carbon and hydrogen atoms, and are characterized by having at least one carbon-carbon triple bond. This triple bond makes them part of the unsaturated hydrocarbons. In this lesson, we will explore the chemistry of alkynes in detail, looking at their properties, structures, and reactions.

Chemical composition

The general formula for alkynes is C n H 2n-2. This formula shows that they have two fewer hydrogen atoms than alkenes, which have double bonds, and four fewer than alkenes, which have only single bonds.

The simplest alkyne is ethyne, commonly known as acetylene, with the chemical formula C 2 H 2. Let's look at the structure of ethyne:

HC≡CH

In the figure above, the lines represent the bonds between atoms. The triple bond is shown as three lines connecting the carbon atoms.

Bonding and geometry

The presence of a triple bond in alkynes results in a linear geometry around the carbon atoms involved in that bond. This linear shape is due to the sp-hybridization of the carbon atoms. Each carbon in a triple-bond uses one sp orbital to form a sigma bond with the other carbon, and the remaining p orbital forms two pi bonds.

This relationship can be visualised as follows:

c ≡ c

In this structural representation, you can see two pi bonds and one sigma bond between the carbon atoms. Therefore, the axial alignment of the p orbitals gives rise to the linear shape of alkynes.

Nomenclature

Alkynes are named according to the IUPAC system, which is based on naming the longest carbon chain that contains a triple bond. The suffix "-ine" is used to indicate the presence of a triple bond. The position of the triple bond is indicated by the lowest numbered carbon atom in the bond.

For example, consider the four-carbon alkyne, butyne:

CH≡C-CH 2 -CH 3

This compound is named 1-butene because the triple bond starts at the first carbon. If the triple bond were moved to the second position, it would be called 2-butene:

CH 3 -C≡C-CH 3

Physical properties

Alkynes have distinctive physical properties due to their linear geometry and the presence of triple bonds. Due to the molecules approaching linear size, enhancing van der Waals interactions, they have higher boiling points than alkenes and alkenes with similar molecular weights.

Alkynes are generally nonpolar, which makes them insoluble in polar solvents such as water. However, they are soluble in nonpolar solvents such as hexane. This is similar to the behavior of other hydrocarbons.

Chemical properties and reactions

The high electron density of the triple bond gives alkynes characteristic chemical reactivity. They can participate in a wide variety of reactions:

1. Addition reactions

Alkynes can undergo addition reactions, where the triple bond is broken and replaced with other atoms. A simple reaction is the hydrogenation of alkynes, forming alkenes or alkenes:

CH≡CH + H 2 → CH 2 =CH 2 (alkene, single addition)
CH 2 =CH 2 + H 2 → CH 3 -CH 3  (alkene, double compound)

2. Hydrohalogenation

Adding hydrogen halide (HX) to alkynes can form haloalkenes or, with excess HX, dihaloalkanes:

HC≡CH + HCl → CH2 =CH-Cl
CH 2 =CH-Cl + HCl → CH 3 CHCl 2

3. Hydration

Alkynes can be converted into ketones (or aldehydes in special cases) by adding water in the presence of specific catalysts, a process known as hydration.

CH≡CH + H 2 O → CH 3 CHO

Synthetic significance

Alkynes are very useful in synthetic organic chemistry. They are used as building blocks in the production of other chemicals and materials. Their ability to participate in addition reactions makes them versatile for building complex molecules.

For example, alkynes can be used to form carbon–carbon bonds, a key step in the synthesis of many organic compounds.

Practical applications

Alkynes are used in a variety of applications around the world:

  • Acetylene is used in welding torches because it produces a very hot flame.
  • Alkynes are involved in the synthesis of drugs.
  • They are leaders in the manufacturing of synthetic fabrics and rubber.

Conclusion

Alkynes are unique compounds that play an important role in both industrial and academic fields of chemistry. Their structure characterized by a carbon-carbon triple bond gives them unique properties that are exploited in a variety of chemical reactions and applications. Understanding their properties and behavior is important for further study and applications in organic chemistry.


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Alkynes

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