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 ↓


Electrophilic addition reactions


Electrophilic addition reactions are an important class of reactions in organic chemistry, particularly notable for reactions with alkenes and alkynes. These reactions involve the addition of an electrophile and a nucleophile to the double or triple bond of an alkene or alkyne. Understanding these reactions is essential for understanding various mechanisms in organic synthesis and biochemistry.

Understanding electrophiles and nucleophiles

An electrophile is an atom or molecule that seeks electrons and has a tendency to accept electron pairs. Electrophiles are often positively charged or neutral molecules that have empty or partially filled orbitals that can accommodate extra electrons. Examples include Br 2, I 2, and HX (where H is hydrogen and X is a halogen).

A nucleophile is an atom or molecule that donates an electron pair. These are usually negatively charged ions or have lone pairs that are available for bonding. Examples include the hydroxide ion (OH -), ammonia (NH 3), and water (H 2 O).

General mechanism of electrophilic addition reactions

The electrophilic addition reaction mechanism usually proceeds in two main steps:

Step 1: Electrophilic attack

In the first step, the electrophile approaches the alkene or alkyne, which has regions of high electron density on the double or triple bond. These electron-rich regions make the carbon-carbon bond nucleophilic. Being electron-deficient, the electrophile attacks the pi electrons of the bond, forming a carbocation intermediate. This step is crucial and determines the rate of the reaction.

C=C + E+ → C+ - C - E

Step 2: Nucleophilic attack

In the second step, the nucleophile attacks the carbocation formed in the first step. The carbocation is an extremely reactive intermediate because of its positive charge and lack of a stable octet. As a result, it reacts rapidly to stabilize itself by accepting an electron pair from the nucleophile.

C+ - C - E + Nu- → C - C - E - Nu

Visualization of electrophilic addition

C=C , E + CC I

Example: Addition of hydrogen halides to alkenes

The addition of a hydrogen halide (such as HBr, HCl, HI) to an alkene is a classic example of electrophilic addition. For example, when HBr is added to ethene, the following steps occur:

Step 1: Formation of the carbocation

The pi bond of ethene attracts the electrophilic hydrogen of the HBr molecule. As the hydrogen accepts electrons, it becomes covalently bonded to one of the carbon atoms. This interaction simultaneously breaks the HBr bond, yielding a bromide ion (Br -) and a carbocation:

CH 2 =CH 2 + HBr → CH 3 -CH + -Br -

Step 2: Nucleophilic attack by the bromide ion

In the second step, the bromide ion, acting as a nucleophile, attacks the carbocation to form the final product:

CH 3 -CH + + Br - → CH 3 -CH 2 -Br

Regioselectivity: Markovnikov's rule

The regioselectivity of electrophilic addition reactions for asymmetric alkenes often follows Markovnikov's rule. This rule is important for predicting addition products:

In electrophilic addition with asymmetric alkenes, the electrophile attaches itself to the less substituted carbon atom, and the nucleophile binds to the more substituted carbon. This results in the formation of the most stable carbocation intermediate.

Consider adding HBr to propane:

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

Hydrogen from HBr binds to the last carbon atom because it results in the formation of a secondary carbocation, which is more stable than the primary carbocation.

Anti-Markovnikov edition

While Markovnikov addition is general, certain conditions lead to anti-Markovnikov addition, usually via a radical mechanism or specific solvents and reagents. This dichotomy is important in specific organic transformations such as hydroboration-oxidation, which result in alcohols from alkenes obeying the anti-Markovnikov rule.

Example: Bromination of ethene

Another prime example of electrophilic addition is the addition of bromine to ethene. This process is indicative of the ability of a molecule such as bromine to act as an electrophile after polarization:

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As bromine approaches the electron-rich alkene, the electrons in the pi bond generate a dipole in the bromine molecule, effectively creating a temporarily polarized molecule with a delta positive bromine atom, which can act as an electrophile.

Br-Br + CH 2 =CH 2 → Br + CH 2 -CH 2 Br -

Cyclic bromonium ion mediation

In a unique twist, the reaction mechanism involves the formation of a cyclic bromonium ion rather than a simple carbocation:

CH 2 Br +

Attack by the bromide ion

Next, the bromide ion generated in the reaction attacks the positively charged center from the opposite direction, resulting in the formation of the trans addition product.

CH 2 -CH 2 Br - + Br + → CH 2 Br-CH 2 Br

Conclusion

Electrophilic addition reactions are fundamental processes widely used in organic chemistry, with different substituents and conditions affecting the final regioselectivity and stereochemistry of the products. From understanding carbocation intermediates to observing the importance of Markovnikov vs. anti-Markovnikov rules, these reactions provide profound insights into the reactivity of unsaturated hydrocarbons. A comprehensive understanding of these reactions is not only helpful in theoretical chemistry but is also invaluable in practical applications such as industrial synthesis and drug development.


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Electrophilic addition reactions

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