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 → Stereoscopic ↓


Chirality and optical activity


Stereochemistry is a branch of chemistry that involves the study of the spatial arrangements of atoms in molecules and their effects on the physical and chemical properties of those molecules. One of the fundamental concepts in stereochemistry is chirality. Chirality plays an important role in the optical activity of organic compounds.

Understanding chirality

Chirality is a geometric property of certain molecules and ions. A molecule or ion is considered chiral if it cannot be superimposed on its mirror image. This property is analogous to the hand shape seen in human hands, where the left hand is the non-superimposed mirror image of the right hand.

For an organic molecule to be chiral, it usually has a carbon atom bonded to four different groups or atoms. This carbon atom is known as the chiral center or stereocenter. The simplest example of a chiral molecule is 2-butanol.

CH3
|
H3C - C - OH
|
CH2CH3

In the structure of 2-butanol, the central carbon is bonded to an H atom, an OH group, a CH3 group, and a CH2CH3 (ethyl) group. Since all of these substituents are different, 2-butanol is a chiral molecule.

Visual representation of chirality

To understand chirality, we can imagine the structure of a chiral molecule and its mirror image:


    
        
        
        
        
        
        
        
        
        Oh
        CH3
        H
        CH2CH3
    

    
    
        
        
        
        
        
        
        
        
        CH3
        Oh
        H
        CH2CH3

In the above SVG representation, we have shown two molecules. The one on the left is the original chiral structure with its substituents, and the one on the right is its mirror image. These two cannot be superimposed on each other, thus demonstrating chirality.

Optical activity

Chiral molecules are often optically active. Optical activity is a property by which a chiral molecule can rotate the plane of polarized light. When polarized light passes through a solution containing a chiral compound, it can be rotated to the left or right.

The direction and degree of rotation are specific for each compound and depend on factors such as concentration, temperature, and the path length of the medium through which the light passes. The two enantiomers (mirror-image isomers) of a chiral compound will rotate light by the same magnitude but in opposite directions.

R and S configurations

The absolute configuration of chiral centers can be described using R and S notation according to the Cahn-Ingold-Prelog priority rules. This system helps determine the spatial arrangement of substituents around a chiral center and provides a standardized way to describe the configuration of a molecule.

Cahn–Ingold–Prelog rule

Here are the steps to determine the R/S configuration:

  1. Assign priorities to the substituents attached to the chiral center based on atomic number; the higher the atomic number, the higher the priority.
  2. Position the molecule so that the lowest priority group points away from you.
  3. Observe the order of priority from 1 to 3. If this order is clockwise, the chiral center is labeled as R (rectus). If the order is counterclockwise, it is labeled as S (sinister).

    
        
        
        
        
        
        
        
        
        OH (1)
        CH3 (2)
        H (4)
        CH2CH3 (3)

In the example above, the substituents are given priorities based on atomic number: OH (oxygen, 1), CH3 (carbon, 2), CH2CH3 (carbon, 3), and H (hydrogen, 4). Looking at the order from 1 to 3 gives a configuration of R or S.

Enantiomers and diastereomers

In stereochemistry, enantiomers and diastereomers are two different types of stereoisomers that arise from chirality.

Enantiomers

Enantiomers are pairs of chiral molecules that are non-superimposable mirror images of each other. They exhibit identical physical properties (e.g. melting point, boiling point) except for the direction of optical rotation. For example, L-lactic acid and D-lactic acid are enantiomers.

Diastereomers

Diastereomers are stereoisomers that are not mirror images of each other. Unlike enantiomers, diastereomers have different physical and chemical properties. An example of this is 2,3-butanediol, which exists in meso and two enantiomeric forms:


    
        
        
        
        
        
        
        
        
        
        
        Oh
        H
        Oh
        H
        C
        C

In the above sequences, the configurations of the central carbon atoms are different, making them diastereomers.

Racemates

A racemate is a 1:1 mixture of two enantiomers that is not optically active. Since the two enantiomers rotate light in opposite directions with equal magnitudes, their effects cancel each other out. An example of this is racemic tartaric acid: a mixture of equal parts D and L tartaric acids.

Importance in biological systems

Chirality is extremely important in biological systems. Many biological molecules, such as amino acids and sugars, are chiral. The activity and function of these molecules often depend on their chirality. For example, only L-amino acids are used in proteins in the human body.

Conclusion

Understanding chirality and optical activity is essential to understanding how molecules interact in chemical reactions and biological systems. The spatial arrangement of atoms in chiral molecules affects their physical and chemical properties, making chirality a fundamental concept in organic chemistry.


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Chirality and optical activity

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