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 ↓


Chirality and optical activity


Chirality is a fundamental concept in stereochemistry, a subfield of organic chemistry that deals with the spatial arrangement of atoms within molecules. Understanding chirality and its relationship to optical activity is important for understanding how molecules differ in structure and function despite having the same atomic composition.

What is chirality?

Chirality comes from the Greek word "cheir," meaning hand. Just as our left and right hands are mirror images of each other but cannot be superimposed on one another, chiral objects have a similar asymmetry.

In chemistry, a molecule is said to be chiral if it cannot be superimposed on its mirror image. This is usually due to the presence of an asymmetric or chiral center, usually a carbon atom bonded to four different substituents.

Chiral center

The most common source of chirality in organic molecules is a tetrahedral carbon atom bonded to four different substituents. Let's consider a molecule with a chiral center:

Chiral carbon (C*)
   ,
  R1 - C* - R2
   ,
  R3
   ,
  R4

In this structure, C* represents the chiral carbon, which is bonded to four different groups represented by R1, R2, R3, and R4

Enantiomers

If a molecule is chiral, it has a non-superimposable mirror image called an enantiomer. Enantiomers are types of stereoisomers that have the same molecular formula and order of bonded atoms but differ in three-dimensional orientation.

Take the example of a simple amino acid:

Enantiomer 1 (D-alanine)
   H
   ,
  COOH - C* - NH2
   ,
   CH3

Enantiomer 2 (L-alanine)
   H
   ,
  COOH - C* - NH2
   ,
   CH3

These two structures are mirror images of each other and cannot be perfectly aligned. They are enantiomers and their spatial arrangement is different.

Optical activity

Optical activity is the ability of a chiral substance to rotate the polarization plane of polarized light. This property arises because chiral molecules interact differently with light due to their spatial arrangement.

Polarized light

Ordinary light vibrates in all directions perpendicular to the direction of travel. In contrast, polarized light vibrates in only one direction. When polarized light passes through an optically active compound, the angle of the light is rotated.

Plane-polarized light -> [chiral compound] -> rotated light

Measuring optical rotation

The extent to which light rotates can be measured using a polarimeter. The specific rotation [α] is calculated using the formula:

[α] = α / (L * C)

Where:

  • α = observed angle of rotation
  • l = length of the sample cell (dm)
  • c = concentration of the solution (g/mL)

Racemic mixture

Racemic mixtures contain both enantiomers of a chiral molecule in equal amounts. The optical activity of one enantiomer is canceled out by the other, making the mixture optically inactive.

Importance of chirality in chemistry

Chirality is not just a topic of academic interest, but also has important practical implications. Many biological molecules are chiral, and often only one enantiomer is biologically active or desired in a drug or biochemical process.

For example, the enantiomers of limonene have different odors: one smells like oranges, and the other smells like lemons. In addition, the drug thalidomide, whose use of one enantiomer caused birth defects, underscores the importance of chirality in drug design.

Chirality in drug design

Pharmaceuticals often require specific enantiomers. A single chiral center can change the way a drug interacts with its biological targets, affecting the drug's effectiveness and safety. Therefore, chemists attempt to synthesize pure enantiomers for use in medicine.

Visualizing chirality: Another example

In addition to chemical structures, chirality can be explained by geometric shapes:

Tetrahedron with 4 different colors
    Hey
   ,
  ,
 R1 R2 R3 R4

In the above 3D model, the central point of the pyramid is the chiral center, and each corner represents different substituents.

Graphical example of chirality

R1 R2 R3 R4

Conclusion

The concepts of chirality and optical activity in stereochemistry are essential for understanding the variation and specificity in molecular behavior, especially in biological systems and pharmaceuticals. Recognizing and manipulating chirality allows chemists to design molecules with desired functionalities and properties, which extends to many fields including drug development, synthetic methods, and materials science.


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