PHD
  1. Inorganic chemistry  1.1. Coordination chemistry  1.1.1. Ligand field theory  1.1.2. Crystal field theory  1.1.3. Molecular Orbital Theory for Coordination Compounds  1.1.4. Stability of Coordination Compounds  1.1.5. Electronic spectra of coordination compounds  1.1.6. Isomerism in Coordination Compounds  1.1.7. Kinetics and mechanism of coordination reactions  1.2. Organometallic Chemistry  1.2.1. Metal Carbonyls  1.2.2. Metal alkyl and aryl  1.2.3. Fischer and Schrock carbonaceans  1.2.4. Oxidative Addition and Reductive Elimination  1.2.5. Metal Hydrides  1.2.6. Catalysis by organometallic compounds  1.2.7. Metallocenes and Sandwich Complexes  1.2.8. CH activation  1.3. Solid state chemistry  1.3.1. Crystal structures and lattices  1.3.2. Band theory and electrical properties  1.3.3. Defects in the crystal  1.3.4. Synthesis of solid state materials  1.3.5. Magnetic and optical properties of solids  1.3.6. Superconductivity  1.3.7. Solid state ionics  1.4. Bio-inorganic chemistry  1.4.1. Metalloproteins and enzymes  1.4.2. Metal ion transport and storage  1.4.3. The role of metals in medicine  1.4.4. Bioinspired catalysis  1.4.5. Metal–DNA interactions  1.4.6. Metal Complexes in Medical Science  1.5. Lanthanides and Actinides  1.5.1. Electronic configuration and oxidation states in lanthanides and actinides  1.5.2. Spectral and Magnetic Properties in Lanthanides and Actinides  1.5.3. Separation and Extraction of Lanthanides and Actinides  1.5.4. Coordination chemistry of f-block elements  1.6. Main Group Chemistry  1.6.1. Chemistry of boron compounds  1.6.2. Chemistry of Silicon and Germanium Compounds  1.6.3. Chemistry of Phosphorus and Sulfur Compounds  1.6.4. Organosilicon chemistry  1.6.5. Noble Gas Chemistry
  2. Organic chemistry  2.1. Reaction mechanism  2.1.1. Nucleophilic substitution reactions  2.1.2. Electrophilic addition and substitution reactions  2.1.3. Elimination reactions  2.1.4. Rearrangement reactions  2.1.5. Radical reactions  2.1.6. Pericyclic Reactions  2.1.7. Photochemical reactions  2.2. Stereoscopic  2.2.1. Chirality and optical activity  2.2.2. Structural analysis  2.2.3. Stereoelectronic effects  2.2.4. Asymmetric synthesis  2.2.5. Dynamic Stereochemistry  2.3. Organometallic Chemistry in Organic Synthesis  2.3.1. Organolithium and organomagnesium reagents  2.3.2. Transition metal catalyzed coupling reactions  2.3.3. Palladium-catalyzed reactions  2.3.4. Olefin Metathesis  2.3.5. Gold and silver catalysis  2.4. Natural products chemistry  2.4.1. Alkaloids and terpenoids  2.4.2. Steroids and Flavonoids  2.4.3. Total synthesis of natural products  2.4.4. Biosynthesis of natural products  2.5. Supramolecular Chemistry  2.5.1. Host-Guest Chemistry  2.5.2. Self-assembly and molecular recognition  2.5.3. Supramolecular Catalysis  2.5.4. Molecular Machines
  3. Physical Chemistry  3.1. Thermodynamics  3.1.1. Laws of Thermodynamics  3.1.2. Chemical Potential and Equilibrium  3.1.3. Statistical thermodynamics  3.1.4. Non-equilibrium thermodynamics  3.2. Quantum Chemistry  3.2.1. Schrödinger equation and its applications  3.2.2. Molecular orbital theory  3.2.3. Density functional theory  3.2.4. Post-Hartree–Fock methods  3.3. Chemical kinetics  3.3.1. Reaction rate theory  3.3.2. Mechanism and rate laws  3.3.3. Catalysis and enzyme kinetics  3.3.4. Reaction dynamics  3.4. Spectroscopy and molecular structure  3.4.1. Infrared Spectroscopy  3.4.2. UV-visible spectroscopy  3.4.3. Nuclear Magnetic Resonance Spectroscopy  3.4.4. Mass Spectrometry  3.4.5. Raman Spectroscopy  3.5. Surface and Colloid Chemistry  3.5.1. Absorption and Catalysis  3.5.2. Surfactants and micelles  3.5.3. Colloidal Stability  3.5.4. Nanomaterials and Interfaces
  4. Analytical chemistry  4.1. Chromatography  4.1.1. Gas Chromatography  4.1.2. High Performance Liquid Chromatography  4.1.3. Thin Layer Chromatography  4.1.4. Ion Chromatography  4.2. Electroanalytical techniques  4.2.1. Voltammetry and Polarography  4.2.2. Conductometry and potentiometry  4.2.3. Colometry  4.3. Spectroscopic Methods  4.3.1. Atomic absorption spectroscopy  4.3.2. Fluorescence Spectroscopy  4.3.3. X-ray diffraction  4.3.4. Electron paramagnetic resonance spectroscopy  4.4. Chemometrics  4.4.1. Data processing and statistical methods  4.4.2. Multidisciplinary analysis  4.4.3. Machine Learning in Analytical Chemistry
  5. Theoretical and Computational Chemistry  5.1. Molecular dynamics simulation  5.2. Quantum chemistry methods  5.3. Computational drug design  5.4. Machine Learning in Chemistry  5.5. Ab initio molecular dynamics
  6. Biophysics and Medicinal Chemistry  6.1. Drug discovery and design  6.2. Enzyme kinetics and inhibition  6.3. Chemical biology approach  6.4. Protein-ligand interactions  6.5. Bioorthogonal chemistry
  7. Materials chemistry  7.1. Polymer chemistry  7.1.1. Polymerization mechanism  7.1.2. Functional Polymers  7.1.3. Biodegradable Polymer  7.1.4. Conducting and semiconducting polymers  7.2. Nano Chemistry  7.2.1. Nanoparticles and nanostructures  7.2.2. Carbon-based nanomaterials  7.2.3. Quantum dots  7.3. Energy and Environmental Chemistry  7.3.1. Battery and Fuel Cell Chemistry  7.3.2. Green chemistry and sustainable materials  7.3.3. Photocatalysis

PHD → Organic chemistry → Reaction mechanism ↓


Electrophilic addition and substitution reactions


Introduction to electrophilic reactions

In organic chemistry, electrophilic reactions are a fundamental class of reactions where an electrophile forms a bond with a nucleophile. This interaction can appear in various forms such as electrophilic addition and electrophilic substitution reactions. Understanding these mechanisms is important for the synthesis and transformation of organic compounds, especially when dealing with complex molecular structures.

Electrophilic addition reactions

Electrophilic addition reactions are important processes that involve the breaking of double or triple bonds in unsaturated compounds, usually resulting in the formation of saturated molecules. These reactions are prevalent, especially in the chemistry of alkenes and alkynes. The general mechanistic sequence is characterized by the addition of an electrophile to a multiple bond, forming a carbocation intermediary, followed by the attack of a nucleophile to yield the final product.

Mechanism of electrophilic addition reactions

The specific mechanism of electrophilic addition can be divided into the following two elementary steps:

  1. The electron-rich double bond of the alkene attacks the electrophile, forming a carbocation.
  2. The nucleophile attacks the carbocation, resulting in the addition product.
C C , , I

In this simplified illustration, an alkene (RCH=CHR) reacts with an electrophile (E^+) to form a carbocation intermediate.

Example reaction: hydrobromination of ethylene

Consider an example of adding hydrogen bromide (HBr) to ethylene:

        CH 2 =CH 2 + HBr → CH 3 -CH 2 Br

This reaction consists of the following steps:

  1. The electron-rich π-bond of ethylene attacks the proton of HBr, forming a carbocation and a bromide ion (Br^−).
  2. The bromide ion attacks the positively charged carbocation, resulting in the formation of bromoethane.

Electrophilic substitution reactions

Unlike addition reactions, electrophilic substitution reactions involve the replacement of an atom in an aromatic compound, usually hydrogen, by an electrophile. These reactions are important in the chemistry of aromatic compounds and include processes such as halogenation, nitration, sulfonation, and Friedel-Crafts alkylation/acylation.

Mechanism of electrophilic substitution reactions

The typical mechanism of electrophilic substitution can be summarized in the following steps:

  1. Generation of active electrophiles.
  2. Formation of an arenium ion intermediate via attack of an activated electrophile on the aromatic ring.
  3. Deprotonation of the arenium ion to restore aromaticity, resulting in the substitution product.
H , I

Example reaction: nitration of benzene

Consider the nitration of benzene, which is a classic electrophilic aromatic substitution reaction:

        C 6 H 6 + HNO 3 + H 2 SO 4 → C 6 H 5 NO 2 + H 2 O

The steps are as follows:

  1. The nitronium ion (NO 2 +) arises from the interaction between nitric acid and sulfuric acid.
  2. NO 2 + ion attacks the π-electron chain of benzene to form a non-aromatic arenium ion.
  3. Finally, the arenium ion loses a proton to regenerate the aromatic system, resulting in the substitution product, nitrobenzene.

Comparative analysis

While both electrophilic addition and substitution reactions involve electrophiles, the contexts in which they occur are quite different. Electrophilic addition is more common in non-aromatic, unsaturated hydrocarbons such as alkenes and alkynes. In contrast, electrophilic substitution is predominant in aromatic systems where restoration of aromaticity is a driving force.

An essential consideration in both types of reactions is the reactivity and stability of the intermediates. For addition reactions, the formation and stability of the carbocation is important. In substitution reactions, the stability of the arenium ion and the subsequent restoration of aromaticity play an important role.

Conclusion

Electrophilic addition and substitution reactions are cornerstones in the field of organic chemistry, serving as mechanisms for transforming simple molecules into more complex structures. Through understanding their pathways and intricacies, chemists can design and synthesize a vast range of organic compounds, optimizing the reactions to create desired structures with specific functionalities.

Whether increasing the saturation level of a compound through addition or generating new aromatic structures through substitution, these reactions are indispensable tools in the organic chemist's arsenal, enabling the exploration and exploitation of the molecular world.


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