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 → Spectroscopy and structural determination ↓


UV-Vis Spectroscopy


UV-Vis spectroscopy, short for ultraviolet-visible spectroscopy, is a powerful analytical technique used in organic chemistry to study chemical compounds and their structures. This method is primarily used to determine the absorption of ultraviolet or visible light by a chemical substance, which can reveal information about the molecular structure and concentrations of the sample.

Principles of UV-Vis spectroscopy

UV-Vis spectroscopy is based on the interaction between light and matter. When light in the ultraviolet or visible range passes through a sample, certain wavelengths are absorbed by electrons present in the molecules of the sample. This absorption is due to electronic transitions, where electrons are excited from a lower energy level (usually the ground state) to a higher energy level.

The absorption of light can be quantitatively described by the Beer–Lambert law, which relates absorbance (A) to the concentration (c) of the absorbing species, the path length (l) of the sample, and the molar absorptivity (ε), a constant that depends on the sample and the wavelength of the light:

A = εlc

Electronic transitions

Organic compounds that contain conjugated systems, such as π- bonds and chromophores, can undergo electronic transitions that can be detected by UV-Vis spectroscopy. The most common electronic transitions include:

  • σ to σ*: Transitions involving electrons in sigma bonds, which typically require high energies and thus occur in the lower wavelength UV region.
  • n to σ*: Transitions involving non-bonding electrons (from lone pair to bonding sigma orbital) usually occur in saturated compounds containing heteroatoms.
  • π to π*: Transitions in which electrons in pi bonds move to restrictive pi orbitals; these are common in unsaturated compounds such as alkanes and fall in the UV-Vis range.
  • n to π*: Transition of non-bonding electrons into delocalized pi orbitals, which is typical in carbonyl compounds.
UV Area Visual field

Applications of UV-Vis spectroscopy

UV-Vis spectroscopy has diverse applications in organic chemistry and related fields. Some of its primary uses are:

Determination of concentrations

The most common use of UV-Vis spectroscopy is to determine the concentration of solutions. By preparing a calibration curve of absorbance versus concentration using a standard compound, the concentration of unknown samples can be determined. This is important in a variety of fields, including pharmaceuticals, environmental monitoring, and biochemical research.

Characterisation of organic compounds

UV-Vis spectroscopy is valuable for characterizing organic compounds because different functional groups absorb light at different wavelengths. The presence of peaks at specific wavelengths in the UV-Vis spectrum can help identify particular functional groups or conjugated systems in a molecule.

Study of reaction kinetics

By monitoring changes in absorption over time, UV-Vis spectroscopy can be used to study reaction kinetics. This allows chemists to determine reaction rates and mechanisms by tracking the creation or consumption of a species in the reaction mixture.

Structure of a typical UV-Vis spectrophotometer

A typical UV-Vis spectrophotometer has the following major components:

  • Light source: This provides the ultraviolet and visible light needed for the measurement. Common light sources include deuterium lamps (for UV) and tungsten lamps (for visible light).
  • Monochromator: This component selects specific wavelengths of light for measurement. It uses a prism or diffraction grating to separate different wavelengths.
  • Sample cell or cuvette: The container in which the liquid sample is placed. It is usually made of quartz or glass, as both materials are transparent to UV and visible light.
  • Detector: This measures the intensity of light passing through the sample. Common detectors include photomultiplier tubes and photodiodes.
light source Monochromator Cuvette Detectors

Interpreting the UV-Vis spectrum

The UV-Vis spectrum shows the absorption (or transmittance) of light against the wavelength of the light. The shape and position of the peaks in the UV-Vis spectrum provide valuable information about the molecule being analyzed.

Example of UV-Vis spectrum interpretation

Consider a simple molecule like 1,3-butadiene. It has a conjugated diene system, which allows π to π* transitions.

Absorbance versus wavelength for 1,3-butadiene:

| Wavelength (nm) | Absorption |

| 240 | 0.8 |
| 260 | 1.2 |
| 280 | 0.6 |

The peak observed at around 260 nm can be attributed to its conjugated system.

Factors affecting UV-Vis absorption

Many factors affect the absorption characteristics of a compound. Some of the notable ones are:

  • Solvent effects: Different solvents can cause a shift in the absorption maximum. Polar solvents generally stabilize the excited state more than the ground state, causing a bathochromic shift (red shift).
  • pH effect: The ionization state of compounds such as phenols and amines can affect their UV-Vis spectra. Changes in pH can produce different protonation states, which can lead to changes in absorption.
  • Concentration: At very high concentrations, there can be deviations from Beer's law due to intermolecular interactions.

In conclusion, UV-Vis spectroscopy is an important technique in organic chemistry for understanding molecular structures, assessing reaction progress, and determining concentration levels. Its straightforward applications and the information it provides make it an indispensable tool for chemists and researchers.


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UV-Vis Spectroscopy

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