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 → Analytical Chemistry → Instrumental methods ↓


Spectroscopy


Spectroscopy is a technique used in analytical chemistry to study the interaction between matter and electromagnetic radiation. It provides essential information about the composition, structure, and properties of substances. At its core, spectroscopy involves the measurement of light absorbed or emitted by a sample, which can be analyzed to infer various characteristics of the sample. The range of spectroscopy methods is vast, each with its own unique applications and principles.

To understand how spectroscopy works, one must understand the fundamentals of light and its interaction with matter. Light behaves as both a wave and a particle, and when it comes into contact with matter, it can be absorbed, reflected, or transmitted. The absorption of light by molecules can cause electronic transitions, vibrational transitions, or both, depending on the energy of the light and the nature of the matter.

Electromagnetic spectrum

The electromagnetic spectrum includes all types of electromagnetic radiation, ranging from high-energy gamma rays to low-energy radio waves. Each region of the spectrum is characterized by a specific wavelength or frequency range. When discussing spectroscopy, the most relevant regions include ultraviolet (UV), visible, infrared (IR), and sometimes microwaves.

Electromagnetic Spectrum:
- Gamma Rays
- X-Rays
- Ultraviolet (UV)
- Visible Light
- Infrared (IR)
- Microwaves
- Radio Waves

In spectroscopy, we often deal with the UV, visible, and IR parts of the spectrum. Because different materials and molecular structures absorb different wavelengths, seeing which wavelengths are absorbed can provide valuable insight into the sample being studied.

Nature of light: wavelength and frequency

Light can be described by both its wavelength and frequency. Wavelength is the distance between successive peaks of a wave, usually measured in meters, nanometers (1 nm = 10-9 m) or micrometers (1 micrometer = 10-6 m). Frequency is the number of wave cycles passing a fixed point in one second, measured in hertz (Hz). There is an inverse relationship between wavelength and frequency; as one increases, the other decreases.

c = λν

Where:

  • c is the speed of light in a vacuum (about 3.00 x 108 meters per second).
  • λ (lambda) is the wavelength.
  • ν (nu) is the frequency.

The energy of a photon can be calculated using the Planck equation:

E = hν

Where:

  • E is the energy of the photon.
  • h is the Planck constant (6.626 x 10-34 Js).
  • ν is the frequency.

Types of spectroscopy

Spectroscopy can be classified based on the region of the electromagnetic spectrum, the specific energy transition occurring in the sample, or the analytical objective. Some common types of spectroscopy are:

1. Ultraviolet-visible (UV-Vis) spectroscopy

Ultraviolet–visible spectrum Ultraviolet Visible

UV-Vis spectroscopy involves measuring the absorption of ultraviolet or visible light by a substance. When a molecule absorbs UV or visible light, electrons in the molecule are excited from lower energy levels to higher energy levels. The wavelength of light absorbed by the molecule can provide information about its electronic structure, which in turn can reveal details about the identity and concentration of the substance.

A common application of UV–vis spectroscopy is to determine the concentration of a solution using the Beer–Lambert law:

A = εbc

Where:

  • A is the absorbance (no units).
  • ε is the molar absorptivity (L/mol·cm).
  • b is the path length of the cuvette (cm).
  • c is the concentration of the solution (mol/L).

2. Infrared (IR) spectroscopy

IR spectroscopy involves the interaction of infrared radiation with matter, causing mainly vibrational changes in molecules. Infrared radiation is lower in energy than visible light, and its interaction with molecules usually involves changes in the vibrational states of chemical bonds. Infrared spectrum Vibration Mode

The infrared spectrum of a compound shows the transmittance or absorbance as a function of the wavelength or frequency of the absorbed infrared light. Different functional groups (e.g., -OH, -NH, -CH groups) absorb at specific frequencies, so IR spectroscopy is very useful for identifying these groups and determining the structure of organic compounds.

3. Nuclear magnetic resonance (NMR) spectroscopy

Nuclear magnetic resonance spectrum Magnetic field interaction

NMR spectroscopy is based on the absorption of radiofrequency radiation by nuclei in a magnetic field. When certain nuclei, such as hydrogen-1 (protons) or carbon-13, are placed in a magnetic field, they can absorb radiofrequency radiation that causes them to transition between different nuclear spin states. The resulting spectrum provides detailed information about the local electronic environment of the atoms in the molecule.

NMR is particularly powerful for determining the structure of organic molecules. The positions of NMR signals, known as chemical shifts, can reveal the types of carbon-hydrogen frameworks present in a molecule. The splitting of these signals can provide information about neighboring atoms, allowing molecular structure to be further elucidated.

4. Mass spectrometry

Although it is not a traditional method of spectroscopy, mass spectrometry is a complementary technique often used in conjunction with spectroscopic methods. Mass spectrometry generates ions from a sample and measures their mass-to-charge ratio. This allows the molecular weight and various structural features of the molecule to be estimated. Mass Spectrum Mass-to-charge ratio

Mass spectrometry is incredibly versatile and can be used for quantitative and qualitative analysis. It is widely used in a variety of fields from pharmaceuticals to environmental science for the identification and quantification of compounds, detection of pollutants, and much more.

Applications and importance of spectroscopy

The main strength of spectroscopy is that it is able to provide detailed information about the molecular structure of a sample, often without requiring large amounts of material or sample preparation. This makes it incredibly valuable in research and industry.

For example, spectroscopy is used for quality control in the pharmaceutical industry, ensuring the authenticity and purity of drugs. In environmental science, spectroscopy can detect the presence of pollutants and toxins, even in minute quantities, thereby aiding in pollution monitoring and control.

In the field of chemistry, spectroscopy is an important tool for determining molecular structures, reaction mechanisms, and the kinetics and thermodynamics of chemical processes. In astronomy, it helps analyze the structure of stars and distant galaxies, increasing our understanding of the universe.

Interpretation of spectral data

Understanding and interpreting spectral data can be complex, but some general guidelines apply. Most spectra are plotted with the response (absorbance, transmittance, etc.) on the y-axis and some measure of energy (wavelength, frequency, chemical shift) on the x-axis.

Peaks at specific locations often indicate the presence of specific atoms, bonds, or functional groups. In UV-Vis spectroscopy, peaks indicate electronic transitions occurring within the sample. In IR spectroscopy, peaks correlate with vibrational modes of chemical bonds.

Noise, baseline drift, and instrumental artifacts can also affect spectral data. Learning how to analyze these spectra involves recognizing and compensating for these potential errors and variations.

Summary

Spectroscopy is an indispensable analytical tool used in many scientific disciplines. By understanding the principles of the interaction of light with matter and analyzing the resulting spectra, scientists can obtain essential information about the chemical and physical properties of a wide range of substances. Whether observing atomic emissions, molecular structures, or identifying unknown compounds, spectroscopy provides a unique gateway into the molecular world.


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Spectroscopy

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