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 ↓


Rearrangement reactions


Rearrangement reactions are an interesting and essential part of organic chemistry. They involve the movement of atoms or groups within a molecule, leading to structural reorganization of the molecule. This type of chemical reaction plays an important role in synthetic chemistry and biological processes. Understanding rearrangement reactions can help chemists design new compounds, study reaction mechanisms, and elucidate metabolic pathways.

Basics of rearrangement reactions

Rearrangement reactions are characterized by the migration of an atom or group from one position to another within the same molecule. The transformation usually results in the formation of an isomer of the original compound. These reactions are often driven by the formation of more stable intermediates or products, such as more stable carbocations or radicals. In general, they can proceed via coordinated pathways or involve discrete intermediates.

Mechanism and energy considerations

In rearrangement reactions, the reaction mechanism involves the transfer of atoms or groups, proceeding through transition states and intermediate states. The energy diagrams of these reactions show the energy changes that occur during the reaction. Rearrangements generally attempt to lower the overall energy of the molecule, leading to a more stable product.

R-CH-CH₃ → R-CH₂-CH₂ (Example of rearrangement resulting in more stable primary and secondary states)

Types of rearrangement reactions

There are many types of rearrangement reactions seen in organic chemistry. Some important types are given below:

1. Wagner–Meerwein rearrangement

The Wagner–Meerwein rearrangement involves the migration of an alkyl group or a hydrogen atom with a lone pair of electrons from one site to another within the carbocation intermediate, which is stabilized through this migration:

(attributes omitted for simplicity)

 [Wagner–Meerwein rearrangement]

   CH₃-CH₂-CH⁺-R → CH₃-CH-CH₂-R⁺

 This rearrangement usually moves the cation center to a more stable position:
 
 1. Rearrangement: CH₃-C⁺(CH₃)(H) → (CH₃)₃C⁺
CH₃-CH₂-CH⁺-R CH₃-CH-CH₂-R⁺ (Rearrangement)

2. Beckmann rearrangement

The Beckmann rearrangement converts oximes to amides. This reaction proceeds via the migration of the alkyl or aryl group from nitrogen to oxygen, forming a new carbon-nitrogen bond. This rearrangement involves:

   R-CO-CH=NOH → R-CO-NH-CH₂

For example, the reaction of cyclohexanone oxime forms a lactam:

   C₆H₁₀-N=OH → ε-caprolactam
R-CO-CH=NOH R-CO-NH-CH₂

3. Claisen rearrangement

The Claisen rearrangement is an example of a [3,3]-sigmatropic rearrangement. It involves the conversion of allyl vinyl ethers into unsaturated carbonyl compounds. The aromatic Claisen rearrangement follows a similar process.

   RCH=CH-CH₂-O-CH₂-CH=CH₂ → RCH=CH-CO-CH₂-CH=CH₂
RCH=CH-CH₂-O-CH₂-CH=CH₂ RCH=CH-CO-CH₂-CH=CH₂

Factors affecting rearrangement reactions

There are several important factors that affect rearrangement reactions. Understanding them can help you predict and control these reactions:

Stability of intermediate goods

Rearrangement tendencies usually correlate with obtaining a more stable intermediate, such as a tertiary carbocation over a secondary or primary carbocation. For example, in the Wagner–Meerwein rearrangement, the carbocation often shifts to provide more substituents at the cationic site.

Sterics and electronic effects

Steric hindrance and electronic effects also affect rearrangement reactions. Bulky groups or electron-donating/withdrawing groups can facilitate or hinder rearrangements, depending on whether they stabilize or destabilize transition states or intermediates.

Reaction conditions

Temperature, catalysts, and solvents can significantly affect the mechanism and efficiency of rearrangement reactions. Higher temperatures often favor coordinated pathways, while catalysts can stabilize intermediates, lowering the activation energy.

Examples of rearrangement reactions in nature and synthesis

Biological processes

Natural biosynthetic pathways often involve rearrangement reactions. For example, the biosynthesis of steroids involves several major rearrangement steps that alter framework structures to produce complex polycyclic molecules.

Synthetic applications

In synthetic organic chemistry, rearrangement reactions are used to strategically modify molecular structures or introduce functional groups into specific regions of the compound.

For example, the process of rearranging alkynes to form ketones is cleverly employed in industry for the synthesis of pharmaceuticals and polymers.

Conclusion

Rearrangement reactions are one of the most versatile tools in the organic chemist's toolkit. They provide routes to create new structures, improve stability, and predict the reactivity of organic molecules. Mastering these reactions reveals an understanding of structural dynamics, favorable electron conformations, and unique molecular structures.


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Rearrangement reactions

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