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 ↓


Rearrangement reactions


Rearrangement reactions in organic chemistry involve structural reorganization of molecules, leading to the formation of new structures. These reactions play an important role in the execution of synthesis methods and serve as a fundamental type of reaction mechanism. The essence of rearrangement reactions is the transfer of a group or atom from one part of the molecular structure to another part within the same molecule.

Understanding rearrangement reactions is important because they often occur in the pathways of many organic processes, including synthetic organic chemistry and biochemical transformations. Generally, rearrangements help transform simple molecules into more complex structures and are essential in the synthesis of a variety of compounds, including pharmaceuticals, natural products, and materials.

Types of rearrangement reactions

Rearrangement reactions can generally be classified into several types depending on the migratory species or functional groups involved. Here are some of the main types of rearrangement reactions that are frequently encountered:

  • 1,2-Rearrangements: These are the most common rearrangement reactions where a substituent moves from one atom to another. Well-known examples include the hydride shift, alkyl shift, and Wagner-Meerwein rearrangement. These rearrangements are important in forming carbocation intermediates.
  • Sigmatropic rearrangement: This type of rearrangement involves the transfer of a σ-bonded atom or group to the π-system, resulting in the formation of a new π-bond. An example of this is the Cope rearrangement.
  • Pericyclic reactions: This class of reactions involves changes in bonds within a cyclic transition state. Cycloadditions, electrocyclic reactions, and sigmatropic shifts are subgroups of pericyclic reactions.
  • Transfer of groups: Typical rearrangements involve the transfer of a simple group such as -OH, -NH 2 resulting in variations in familiar compounds, for example, Beckmann rearrangement and Hofmann rearrangement.

Mechanisms of rearrangement reactions

Rearrangement reactions can be grouped based on how migration occurs in terms of mechanical pathways:

  1. Nucleophilic substitution mechanism: In some cases, rearrangement occurs via nucleophilic substitution pathway. Here, a nucleophile attacks an electrophilic center resulting in rearrangement.
  2. Electrophilic substitution mechanism: Similarly, electrophilic species can induce rearrangements, especially in aromatic systems where electron rich aromatic substituents facilitate the transfer of substituent groups.

Examples of rearrangement reactions

Wagner–Meerwein rearrangement

The Wagner-Meerwein rearrangement is a classic example of a 1,2-rearrangement. During this process, carbocations undergo rearrangement, involving a shift of the alkyl or aryl group, forming a more stable carbocation intermediate.

// Reaction: Tertiary Carbinol to Pinacol (common example) R  C+ -- R' ---> R -- C -- R'' / R''

This rearrangement proceeds via a carbocationic intermediate where stability is the driving force behind the rearrangement. If a tertiary carbocation can be formed, it is often more stable than a secondary or primary carbocation, thus becoming the preferred transformation.

Beckmann rearrangement

The Beckmann rearrangement involves the conversion of oximes into their corresponding amides. The rearrangement occurs under acidic conditions and involves a nitrogen atom.

// Reaction: Oxime to Amide R--C(R')(OH)/N --R'' --> R--C(=O)--NH--R''

In this rearrangement, the –OH group adjacent to nitrogen in the oxime is converted into an amide group -C(=O)-NH-.

Cope rearrangement

The Cope rearrangement is a popular example of a sigmatropic rearrangement, where 1,5-diene undergoes bond reorganization at high temperatures.

// Reaction: Cope Rearrangement R--C=C--C--C=C--R' → R'--C=C--C--C=C--R

Switching of σ bonds and reorganization of π bonds characterize this reaction, which stabilizes the molecular structure through a coordinated mechanism. It is commonly employed in the synthesis of cyclohexadienes.

Detailed steps involved in rearrangement reactions

The mechanism of rearrangement reaction involves several important steps, which are broadly classified as follows:

  1. Formation of stable intermediates: Rearrangements generally begin with the formation of a reactive intermediate such as a carbocation, carbanion, or radical. The stability and reactivity of the intermediate significantly influence the course of the reaction.
  2. Transfer/Transposition of groups: The main thing in this process is the transfer of atoms or groups from one part of the molecule to another. This transfer proceeds to obtain a more stable electronic arrangement.
  3. Formation of the product: After the rearrangement of the groups, the next steps focus on stabilizing the newly arranged structure, leading to the formation of the final rearranged product.

Factors affecting rearrangement reactions

Several factors can affect rearrangement reactions, which determine whether or not the reaction will occur and what its final outcome will be:

  • Stability of intermediates: The stability of the migrating group and the intermediate formed determines the possibility and direction of rearrangement. Highly stable intermediates promote rearrangement.
  • Electronic effects: Hyperconjugation, resonance, and inductive effects can stabilize the intermediates that undergo rearrangement.
  • Stereochemistry: The stereochemistry of a molecule can affect the product formed. Some rearrangements are stereospecific, leading to products with well-defined stereochemistry.
  • Intramolecular/intermolecular rearrangement: The rearrangement can occur within a molecule or between two molecules, such as [3,3]-sigmatropic rearrangement for intramolecular cases.

Conclusion

Rearrangement reactions are an integral part of organic chemistry and provide a fascinating glimpse into the structural reorganization of molecules. These reactions demonstrate the power of chemical reactivity, which directs the transformation of molecular structures into new entities through the seemingly simple migration of atoms or groups. An understanding of rearrangement reactions provides organic chemists with deep insights into reaction mechanisms, enabling the design and synthesis of complex molecules with precision.


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Rearrangement reactions

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