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 ↓


Addition reactions


Addition reactions are a fundamental class of chemical reactions in organic chemistry. These reactions involve the addition of atoms or groups at a multiple bond such as a double or triple bond. They are characterized by an increase in the number of substituents on the organic molecule, typically converting unsaturated compounds into saturated compounds. Understanding addition reactions is important for the synthesis of a vast range of organic compounds.

Basic concepts of addition reactions

Addition reactions generally occur with alkenes or alkynes, where a double or triple carbon-carbon bond is present. In an addition reaction, the pi bond is broken and new sigma bonds are formed between the added atoms. Reactivity in addition reactions generally arises from the presence of electron-rich pi bonds that are susceptible to attack by electrophiles or radicals.

General equation

C=C + XY → XCCY

This equation summarizes how a typical electrophilic addition with an alkene proceeds.

Types of addition reactions

Addition reactions can be classified based on the type of reactants and the mechanism by which they proceed.

1. Electrophilic addition reactions

Electrophilic addition is one of the most common types of addition reactions. Here, an electrophile attacks an electron-rich double or triple bond of an unsaturated compound.

Example: Hydrohalogenation

In hydrohalogenation hydrogen halides such as HCl, HBr are added to the alkane. For example: 

CH₂=CH₂ + HBr → CH₃-CH₂Br

The electrophile (H⁺) attacks the double bond of ethylene, after which the bromide ion is added.

Mechanistic description of electrophilic addition

This mechanism can be divided into two important steps:

  1. Formation of a carbocation intermediate by attack of an electrophile.
  2. Attack of the nucleophile on the carbocation, resulting in the formation of the addition product.

2. Nucleophilic addition reactions

Nucleophilic addition is common with compounds containing polar multiple bonds, such as carbon-oxygen (C=O) in carbonyl. The nucleophile attacks the electrophilic carbon atom of the carbonyl group.

Example: Addition of Grignard reagents

Grignard reagents (RMGX) are excellent nucleophiles that react with carbonyl compounds to form alcohols after protonation. 

R-MgX + R'C=O → R-COHR'

The Grignard attacks the carbonyl carbon, forming an alkoxide ion, which upon protonation gives the alcohol.

3. Radical addition reactions

Radical addition reactions occur via free radical intermediates. A free radical is an atom or group of atoms that has an unpaired electron, making them highly reactive.

Example: Addition of HBr in the presence of peroxide (anti-Markovnikov addition)

In the presence of peroxides, HBr binds to alkenes via a radical chain mechanism resulting in anti-Markovnikov regioselectivity. 

CH₂=CH₂ + HBr (peroxide) → CH₂Br-CH₃

This process involves initiation (formation of radicals), expansion (addition of radicals to the alkene) and termination steps.

System flow

Illustrative mechanism diagram

Below are diagrams showing a basic electrophilic addition reaction mechanism:

      [R''-C=CR'] + E⁺ → [R''-C⁺-C(-)R'] → [R''-CC-R'] | | EN

This diagram summarizes how the electrophile 'E⁺' initially attacks the double bond, resulting in the formation of a carbocation, which is then attacked by the nucleophile 'N'.

Transition state concepts

Understanding the transition states of these reactions can be important for observing energy changes during the process. Each addition step involves crossing an energy barrier, which is usually associated with the formation of an unstable high-energy transition state.

Regiochemistry and stereochemistry of addition reactions

Reactions in organic chemistry occur with specific orientation and stereochemical outcomes. The two key concepts are:

Regional selectivity

In many electrophilic addition reactions, the orientation of the reaction product is dictated by Markovnikov's rule, which states that when HX is added to an alkene, the hydrogen atom attaches to the carbon with more hydrogen substituents, while the halide attaches to the carbon with fewer hydrogen substituents.

Visual example:

CH₃-CH=CH₂ + HCl → CH₃-CHCl-CH₃

According to the Markovnikov rule, hydrogen from HCl attaches to the carbon with more hydrogen, and Cl₂ attaches to the less substituted carbon in propane.

Stereoselectivity and stereospecificity

These terms describe the consequences of dealing with stereoisomers. Some addition reactions are stereoselective, preferring one stereoisomer over the others.

Syn and anti addition

In syn addition, the two groups add to the same side of the double bond, while in anti addition, they add to opposite sides.

The hydrogenation of alkenes using metal catalysts usually proceeds via syn addition:

C=C + H₂ (Pt catalyst) → HCCH

Relevant examples:

The conversion of cyclohexene to cyclohexene shows syn addition:

      HH   / C₆H₁₀ + H₂ (Pt) → C₆H₁₂ (Syn addition) /  HH

Factors affecting addition reactions

The rate and outcome of addition reactions are influenced by several factors:

Substrate composition

The nature of the alkene or alkyne can significantly affect the reactivity. For example, more substituted alkenes often react faster due to the stability of the carbocation formed.

Solvent effect

The choice of solvent can stabilize or destabilize the ionic intermediate, affecting the reaction pathway. Polar solvents are excellent for reactions involving charged intermediates.

Temperature

Higher temperatures increase reaction rates by providing enough kinetic energy to overcome the activation energy barriers.

Applications of addition reactions

Addition reactions are important in a variety of industrial and laboratory syntheses of organic compounds. Here are some of the major applications:

Industrial applications

Hydrogenation reactions, which are necessary to convert unsaturated fats into saturated fats, are major examples of industrial applications of addition reactions. This process increases the melting point and shelf life of oils.

Synthesis of pharmaceuticals

Many pharmaceutical compounds are synthesized or modified using addition reactions. For example, alkenes are converted into alcohols, ketones, and carboxylic acids, which are structurally important in drug design.

Polymerization processes

Polymer chemistry relies heavily on addition reactions. Monomers containing carbon-carbon double bonds join together to form polymers via addition mechanisms.

In summary, to understand addition reactions it is necessary to understand not only their types and mechanisms but also their wider implications in chemistry and industry.


Undergraduate → 2.5.3


U
username
0%
completed in Undergraduate

← Prev (2.5.2)
Elimination reactions
Next (2.5.4) →
Radical reactions

Comments 



Addition reactions

https://www.chemistryelite.com/ug/2.5.3?ceal=en