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 ↓


IR Spectroscopy


Infrared (IR) spectroscopy is a powerful technique used to identify and study chemicals by analyzing the interaction of infrared light with molecules. In organic chemistry, it is particularly useful for determining the structure of organic compounds by identifying functional groups.

Principles of IR spectroscopy

When molecules absorb infrared light, they experience changes in their vibrational states. These vibrations are associated with the bonds within the molecule. Each bond in the molecule can vibrate in a number of ways; these include stretching (where the bond lengthens and shortens) and bending (where the angle between the bonds changes).

The specific frequencies at which the molecule absorbs IR light correspond to the energies needed to change the vibrational states of the molecule. Each different type of bond, or a particular bond in a molecule, will have a specific absorption spectrum. By analyzing this spectrum, chemists can infer which functional groups are present in the molecule.

Components of IR spectrometer

An IR spectrometer has three main components:

  • Radiation source: It emits a broad spectrum of infrared light.
  • Monochromator: This separates the different frequencies of IR light so they can be measured individually.
  • Detector: This measures the intensity of transmitted or reflected IR light, and provides data that can be used to generate an IR spectrum.

IR spectrum

The IR spectrum is a graph of transmitted IR light (on the y-axis) versus frequency or wavelength (on the x-axis). It displays peaks corresponding to specific energies absorbed by the molecular vibrations of the sample. The frequency of light is usually stated in wave numbers, which are expressed in reciprocal centimeters (cm-1).

Wave number (cm-1) Communication %

The most informative major regions in the IR spectrum are the following:

  • Fingerprint region (600-1500 cm-1): This region contains complex peaks unique to each molecule, much like a fingerprint.
  • Functional group region (1500-4000 cm-1): This is the region where stretches due to functional groups (e.g. -OH, -NH, C=O) appear.

Interpreting the IR spectrum

To interpret the IR spectrum, identify the important peaks associated with bond vibrations and correlate them with possible functional groups within the molecule. Here's how to identify some common functional groups:

Hydroxyl group (-OH)

The peak of the -OH group lies between 3200-3600 cm-1. This width arises due to hydrogen bonding.

Oh Stretch

Example: Consider ethanol, which has a characteristic peak due to the –OH stretching vibration.

C2H5OH

Carbonyl group (C=O)

The carbonyl group has a sharp, strong peak that typically occurs near 1700 cm-1. This is a key indicator for the presence of aldehydes, ketones, carboxylic acids, esters, and other carbonyl-containing compounds.

C=O Stretch

Example: Acetone will exhibit a prominent C=O band.

CH3COACH3

Amino group (-NH2)

The amino groups show two NH stretching peaks due to symmetric and asymmetric stretching, appearing around 3300-3500 cm-1.

NH2 Stretch

Example: Ammonia (NH3) would show these bands.

Analysis of complex IR spectra

Analyzing complex spectra involves comparing known spectral data from similar known structures. When multiple functional groups are present, the spectra can become complex. There may be overlapping peaks, especially in the fingerprint region, which complicates the analysis.

For substances with known structure, comparison of intensities, exact frequencies, and shapes (such as sharp or broad peaks) are important for determining molecular properties.

Limitations of IR spectroscopy

Despite its advantages, IR spectroscopy has limitations:

  • Lack of detail: IR spectroscopy provides information about functional groups, but it does not elucidate the complete molecular structure.
  • Complex mixtures: IR is less effective for complex mixtures because overlapping peaks can obscure the data.
  • Nonpolar bonds: Nonpolar bonds such as O=O do not absorb IR radiation, causing the spectra of homonuclear diatomic molecules to disappear.

Applications of IR spectroscopy

IR spectroscopy is widely used in:

  • Identification: Confirming the presence of functional groups in an organic compound.
  • Quality control: Ensuring purity and composition of materials manufactured.
  • Reaction monitoring: Observing the progress of chemical reactions in real time by consumers of the reactants.

Because of these diverse applications, IR spectroscopy is a fundamental tool for organic chemistry analysis in both academic and industrial settings.

Conclusion

IR spectroscopy provides a window into the vibrational world of molecules, revealing clues about the structure and functional groups of organic compounds. Although it has limitations, its ease of use and rapid analysis make it indispensable in many fields.

Understanding IR spectra gives chemists the knowledge they need to solve molecular puzzles and advance their research or product development, underscoring the essential role this technique plays in science and industry.


Graduate → 2.2.2


U
username
0%
completed in Graduate

← Prev (2.2.1)
UV-Vis Spectroscopy
Next (2.2.3) →
NMR Spectroscopy

Comments 



IR Spectroscopy

https://www.chemistryelite.com/g/2.2.2?ceal=en