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 → Stereoscopic ↓


Stereoelectronic effects


In the field of organic chemistry, understanding the effects of electron distribution and atomic arrangement in molecules is crucial to understanding many of their properties and reactivity. At the heart of this understanding lies the concept of stereoelectronic effects. These effects describe how the spatial arrangement of atoms (stereochemistry) affects the electronic characteristics and reactivity of molecules. By better understanding these interactions, chemists can predict and manipulate chemical behavior with greater accuracy.

What are stereoelectronic effects?

Stereoelectronic effects are the effects that the geometry or three-dimensional arrangement of atoms and orbitals in a molecule has on its electronic structure and properties. These effects can be observed in various processes such as reactions, stability and molecular interactions. These effects play an important role in determining the outcome of many organic reactions, where even slight changes in molecular geometry can lead to different products.

Theory of stereoelectronic effect

At its core, stereoelectronic effects are based on molecular orbital theory, which provides a framework for understanding how atomic orbitals combine to form molecular orbitals. There are two major principles behind these effects:

  • Sigma (σ) and pi (π) interactions: The alignment of sigma and pi bonds with non-bonding or bonding orbitals can enhance or inhibit certain chemical reactions.
  • Structural preference: The spatial arrangement of substituents can affect the energy barriers for rotation about bonds, and ultimately affect molecular stability and reactivity.

Examples of stereoelectronic effects

1. Anomeric effect

The anomeric effect is a classic example of a stereoelectronic effect, observed mainly in carbohydrate chemistry. It describes the preference of certain substituents to adopt the axial position in the chair conformation of cyclic saccharides, even when the equatorial position is expected to be more stable due to steric factors.

RO-C_1(H)-C_2(OH) → Axial preference in pyranosis due to anomeric effect

This effect is mainly due to the n → σ* interaction, where the axial lone pair electrons on the oxygen atom can donate to the sigma antibonding orbital of the adjacent C-X bond (X is a substituent group), lowering the overall energy.

2. Hyperconjugation

Hyperconjugation is the displacement of electrons from a sigma orbital (usually CH or CC) by overlapping it with an adjacent empty or partially filled p-orbital or pi-orbital, thereby obtaining an extended molecular orbital. This effect, among other phenomena, explains the stability of alkenes:

        CH_3-CH=CH_2 vs CH_2=CH-CH_3

Here, the alkene with more substituents on the double bond is more stable due to greater hyperconjugation, which stabilizes the system by displacing the electron density.

3. Peri-planar effect

Peri-planarity involves the effect of substituents located in close spatial proximity. This is notable in the similar or opposing arrangement of substituents relative to the functional group, which affects mechanisms such as elimination and substitution reactions.

For example, E2 elimination reactions are highly favored when the leaving group and the hydrogen atom that is being removed are antiplanar to each other. This geometry allows for optimal overlap of orbitals, making pi bond formation easier.

CH_3-CH(X)-CH_2Y → Antiperiplanar elimination for E2 mechanism

4. Baldwin's Laws

Baldwin's rules delineate the stereoelectronic preferences for various ring closure reactions, establishing which conformations are favorable for cyclization. The orientation of the substituents during these closures significantly affects the rate and success:

Consider the closure of gamma-lactone, where the angles and orbitals involved affect the reaction pathway.

HO-(CH_2)_3-COOH → Favorable closure for γ-lactone under certain conditions

Visual representation

Sigma BondPi Bond Hyperconjugation overlap

Implications in synthesis and reactivity

Stereoelectronic effects guide synthetic chemists in choosing reaction pathways and optimizing yields. By understanding these interactions, chemists can design reactions with high specificity and efficiency. Consider the following practical implications:

  • Enhanced selectivity: By aligning substrates to favor specific stereoelectronic effects, reaction selectivity can be enhanced.
  • Energy minimization: Selecting configurations and orientations that minimize the transition state energy through favorable orbital interactions can minimize reaction barriers.
  • Design of catalysts: Stereoelectronic insights can lead to the development of catalysts that preferentially activate specific pathways.

Conclusion

The concept of stereoelectronic effects is a fundamental part of stereochemistry and molecular orbital theory, which provide profound insight into the behavior and reactivity of molecules. By integrating knowledge of stereochemistry with electronic interactions, chemists can better predict and influence the outcomes of organic reactions. As a field of study, this understanding continues to evolve, promising new discoveries and innovations in chemical synthesis, drug design, and materials science.


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