Graduate
  1. Physical Chemistry  1.1. Thermodynamics  1.1.1. Laws of Thermodynamics  1.1.2. Enthalpy and heat capacity  1.1.3. Entropy and free energy  1.1.4. Phase Equilibrium  1.1.5. Statistical thermodynamics  1.1.6. Thermodynamic cycle  1.1.7. Fugacity and activity  1.2. Quantum Chemistry  1.2.1. Principles of quantum mechanics  1.2.2. Schrödinger Equation  1.2.3. Particle in a box  1.2.4. Operators and eigenvalues  1.2.5. Atomic orbitals  1.2.6. Molecular orbital theory  1.2.7. Perturbation theory  1.2.8. Valence bond theory  1.2.9. Hybridization and chemical bonding  1.3. Chemical kinetics  1.3.1. Rate laws and reaction mechanisms  1.3.2. Collision theory  1.3.3. Transition state theory  1.3.4. Enzyme Kinetics  1.3.5. Chain Reactions and Polymerization  1.3.6. Photochemical reactions  1.4. Statistical mechanics  1.4.1. Partitioning functions  1.4.2. Molecular distribution functions  1.4.3. Boltzmann Distribution  1.4.4. Bose–Einstein and Fermi–Dirac statistics  1.5. Spectroscopy  1.5.1. Rotational Spectroscopy  1.5.2. Vibrational Spectroscopy  1.5.3. Electronic Spectroscopy  1.5.4. Nuclear magnetic resonance spectroscopy  1.5.5. Mass Spectrometry  1.5.6. Raman Spectroscopy  1.5.7. Electron paramagnetic resonance spectroscopy  1.6. Surface and colloidal chemistry  1.6.1. Absorption isotherm  1.6.2. Surface tension and wetting  1.6.3. Colloidal Stability  1.6.4. Catalysis  1.6.5. Emulsions and micelles  1.7. Electrochemistry  1.7.1. Nernst equation  1.7.2. Electrochemical cells  1.7.3. Conductivity and mobility  1.7.4. War  1.7.5. Fuel cells  1.7.6. Electrolysis
  2. Organic chemistry  2.1. Reaction mechanism  2.1.1. Nucleophilic substitution reactions  2.1.2. Electrophilic addition reactions  2.1.3. Elimination reactions  2.1.4. Rearrangement reactions  2.1.5. Radical reactions  2.1.6. Pericyclic reactions  2.2. Spectroscopy and structural determination  2.2.1. UV-Vis Spectroscopy  2.2.2. IR Spectroscopy  2.2.3. NMR Spectroscopy  2.2.4. Mass Spectrometry  2.2.5. X-ray crystallography  2.3. Stereoscopic  2.3.1. Chirality and optical activity  2.3.2. Structural analysis  2.3.3. Geometrical isomerism  2.3.4. Dynamic Stereochemistry  2.4. Organometallic Chemistry  2.4.1. Organolithium and organomagnesium reagents  2.4.2. Palladium-catalyzed cross-coupling reactions  2.4.3. Transition Metal Complexes  2.4.4. Metal–carbon bond  2.5. Polymer chemistry  2.5.1. Polymerization mechanism  2.5.2. Polymer Characteristics  2.5.3. Biodegradable Polymer  2.5.4. Conducting polymer  2.5.5. Supramolecular polymers  2.6. Medicinal chemistry  2.6.1. Drug design and development  2.6.2. Pharmacokinetics and pharmacodynamics  2.6.3. Structure-activity relationships  2.6.4. Molecular docking and drug screening
  3. Inorganic chemistry  3.1. Coordination chemistry  3.1.1. Crystal field theory  3.1.2. Ligand field theory  3.1.3. Spectrochemical Series  3.1.4. Chelation and stability  3.2. Organometallic Chemistry  3.2.1. Metal Carbonyls  3.2.2. Catalysis by organometallic complexes  3.2.3. Metallocenes  3.3. Bio-inorganic chemistry  3.3.1. Metalloproteins and enzymes  3.3.2. The role of metals in biological systems  3.3.3. Metal ion transport and storage  3.4. Solid state chemistry  3.4.1. Crystal Structures  3.4.2. Band theory of solids  3.4.3. Superconductors  3.4.4. Defects in the crystal  3.5. Lanthanides and Actinides  3.5.1. Electronic configuration in lanthanides and actinides  3.5.2. Coordination chemistry of the lanthanides  3.5.3. Magnetic Properties of Lanthanides
  4. Analytical chemistry  4.1. Chromatography  4.1.1. Gas Chromatography  4.1.2. High Performance Liquid Chromatography  4.1.3. Thin Layer Chromatography  4.2. Spectroscopic Techniques  4.2.1. Atomic absorption spectroscopy  4.2.2. X-ray diffraction  4.2.3. Inductively coupled plasma spectroscopy  4.3. Electroanalytical methods  4.3.1. Potentiometry  4.3.2. Voltammetry  4.3.3. Colometry  4.4. Mass Spectrometry  4.4.1. Ionization Technique  4.4.2. Fragmentation Pattern  4.5. Chemometrics  4.5.1. Multidisciplinary analysis  4.5.2. Machine Learning in Chemistry
  5. Theoretical and Computational Chemistry  5.1. Molecular dynamics simulation  5.1.1. Force fields and energy minimization  5.1.2. Monte Carlo simulation in molecular dynamics simulations  5.2. Quantum chemical methods  5.2.1. Hartree–Fock theory  5.2.2. Density functional theory  5.2.3. Semi-empirical methods  5.3. Computational drug design  5.3.1. Molecular Docking  5.3.2. QSAR Modeling  5.3.3. Virtual Screening
  6. Biochemistry  6.1. Enzyme Kinetics  6.1.1. Michaelis-Menten kinetics  6.1.2. Inhibition mechanism  6.2. Metabolism and Bioenergetics  6.2.1. Glycolysis  6.2.2. Citric acid cycle  6.2.3. Electron transport chain  6.3. molecular Biology  6.3.1. DNA replication and repair  6.3.2. Protein synthesis  6.3.3. Gene Regulation  6.4. Structural Biochemistry  6.4.1. Protein Folding  6.4.2. Membrane Biophysics
  7. Environmental Chemistry  7.1. Atmospheric Chemistry  7.1.1. Greenhouse gases  7.1.2. Ozone depletion  7.1.3. Air pollutants and smoke  7.2. Water Chemistry  7.2.1. pH and water hardness  7.2.2. Wastewater treatment  7.2.3. Aquatic Chemistry  7.3. Soil Chemistry  7.3.1. Heavy metal contamination  7.3.2. Soil pH and Buffering  7.3.3. Nutrient cycling  7.4. Toxicology and Chemical Safety  7.4.1. Toxicokinetics  7.4.2. Risk Assessment in Toxicology and Chemical Safety in Environmental Chemistry  7.4.3. Effects of pollutants on the environment

Graduate → Organic chemistry → Reaction mechanism ↓


Radical reactions


Radical reactions are an important class of reactions in organic chemistry that involve species with unpaired electrons. Radicals are highly reactive due to the presence of the unpaired electron, which makes them important in a variety of chemical transformations. Understanding the mechanisms and applications of radical reactions is important for manipulating organic compounds in synthetic chemistry, biochemistry, and industrial processes.

What are radicals?

In simple terms, a radical is an atom, molecule, or ion that has an unpaired valence electron. This unpaired electron makes radicals highly reactive as they tend to pair with electrons from other entities to achieve more stable electronic configurations. Radicals can form through several mechanisms, including homolytic bond cleavage, where a bond breaks symmetrically and each fragment retains one of the shared electrons.

Formation of radicals

The formation of radicals usually involves the following processes:

  • Isoelectric cleavage, where a bond breaks evenly, and each atom within the bond retains one electron, forming two radicals.
 r—x → r• + x•

This reaction represents the isotropic fission of the molecule R—X into radicals R• and X•. This type of bond fission requires energy, often provided by heat or light, to overcome the bond dissociation enthalpy.

Radical chain reactions

One of the best-known mechanisms involving radicals is the radical chain reaction, which consists of three major steps: initiation, propagation, and termination.

Initiation

The initial step involves the formation of radicals from non-radical species. Typically, this requires an external energy source such as heat, light, or a catalyst. A common example involves the homolysis of halogens:

 Cl2 → 2 Cl•

Here, the chlorine molecules absorb energy and break down into two chlorine radicals.

Propagation

During propagation, radicals react with stable molecules to form new radicals, thus maintaining the chain reaction. For example, in the chlorination of methane:

 CH4 + Cl• → CH3• + HCl
 CH3• + Cl2 → CH3Cl + Cl•

This process continues until the reactants are used up or termination occurs.

Termination

In this step, the radicals combine with each other and are deactivated, forming stable, non-radical products:

 Cl2 + Cl2 → Cl2
 CH3• + Cl• → CH3Cl
 CH3• + CH3• → C2H6

This stops the chain reaction, and the radicals are prevented from spreading further.

Types of radical reactions

Radical reactions can vary widely depending on the nature of the radical and the type of substrate involved. The main types include:

Substitution reactions

In radical substitution, the radical replaces an atom or group in the molecule. A common example of this is the halogenation of alkenes:

 RH + X2 → RX + HX

In this reaction, a halogen radical X• abstracts a hydrogen atom from RH to form HX, leaving behind another radical which can continue the chain reaction.

Addition reactions

In radical addition reactions, radicals add to multiple bonds, breaking them and forming new radicals. A classic example of this is the addition of hydrogen bromide to an alkene via the radical mechanism:

 RO • + HBr → ROH + Br •
 Br• + CH2=CH2 → CH2Br–CH2•

Visual example of the radical chlorination reaction path

Cl2 2 CL• CH4 CH3• + HCl Cl2 CH3Cl2 + Cl2

Applications and significance

Radical reactions are used in many areas due to their versatility and efficiency:

  • Industrial chemistry: Used in polymerization processes and the manufacturing of certain types of plastics.
  • Organic synthesis: Essential for adding functionality to molecules, especially in the creation of complex organic molecules.
  • Biochemistry: Radicals play a role in biological processes, including enzymatic reactions and cellular signaling.

Conclusion

Radical reactions are fundamental to a wide spectrum of chemical processes. Understanding their mechanisms allows chemists to skillfully engineer these reactions to produce desired results. The elementary steps of initiation, propagation, and termination determine how radicals behave, which contributes to their utility in a variety of applications. By carefully and strategically using the reactive nature of radicals, chemists can manipulate complex reactions to synthesize new compounds, advance industrial processes, and explore biochemical pathways.


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Radical reactions

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