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 → Spectroscopy and structural analysis ↓


Infrared Spectroscopy


Introduction

Infrared spectroscopy is a technique used in organic chemistry to determine the functional groups present in a molecule. It does this by measuring the absorption of infrared radiation by the sample material as a function of wavelength or frequency. The resulting spectrum is a unique fingerprint that can help identify chemical substances.

Principle of infrared spectroscopy

Infrared radiation has a longer wavelength and lower frequency than visible light. When a molecule absorbs infrared radiation, it leads to the excitation of vibrational modes of the molecule. These vibrational modes are related to the stretching and bending of chemical bonds within the molecule. Different functional groups absorb specific frequencies of IR radiation, which can be represented in the IR spectrum.

Electromagnetic spectrum

Infrared spectroscopy falls in the infrared region of the electromagnetic spectrum. The infrared region lies between visible light and microwaves and is divided into three regions:

  • Near infrared (NIR): 0.78 to 2.5 μm
  • Mid infrared (MIR): 2.5 to 50μm
  • Far infrared (FIR): 50 to 1000μm

Molecular vibrations

The interaction of infrared radiation with a molecule can produce a variety of molecular vibrations. The two main types of vibrations observed in infrared spectroscopy are stretching and bending.

Stretching

  • Symmetrical stretch: Both atoms move toward or away from the central atom at the same time, maintaining the symmetry of the molecule.
  • Asymmetric pull: One atom moves toward the central atom while the other moves away.

Bending

  • Scissor movement: Two atoms move towards each other and away from each other.
  • Oscillation: Two atoms move in the same direction.
  • Wagging: Two atoms move in opposite directions in out-of-plane motion.
  • Rotation: Rotational motion around the bond axis.

Understanding IR spectra

The IR spectrum is a graph of transmittance or absorbance against the frequency or wavelength of infrared light. The x-axis usually represents wavenumber, measured in cm -1, while the y-axis represents percent transmittance.

Example of IR spectrum

Consider the IR spectrum of ethanol (C 2 H 5 OH):

Wave number (cm -1) % Communication C–H stretch O–H stretch

In the ethanol spectrum, the broad peak around 3300-3500 cm -1 is due to O–H stretching, which is indicative of alcohol. The peaks in the range of 2800-3000 cm -1 are due to C–H stretching in the alkyl group.

Normal IR absorption

The typical absorption bands of different functional groups are as follows:

Functional Group Wave number range(cm -1) Type of vibration
Hydrocarbons 2850-2960 C–H stretching
Alkene 1620-1680 C=C stretching
Alkynes 2100-2260 C≡C stretching
Alcohol 3200-3550 O–H stretching
Carboxylic acid 2500-3000 Extensive O–H stretching
Amin 3300-3500 N–H stretching
Aldehyde 1720-1740 C=O stretching
Ketones 1705-1725 C=O stretching
Aster 1735-1750 C=O stretching

Sample preparation

The preparation of samples for IR spectroscopy can be done in several forms:

  • Neat liquid: The sample is run as a thin film between two salt plates.
  • KBr pellet: Solid samples are pelleted by grinding them with potassium bromide.
  • Mulling technique: The sample is mixed with a mulling agent such as mineral oil and spread on an IR card.

Applications of IR spectroscopy

Infrared spectroscopy is widely used in various fields:

  • Identification of functional groups: Quick identification of functional groups in a molecule through specific absorption bands.
  • Structural elucidation: Provides insight into molecular structure by identifying different functional groups and bond configurations.
  • Quality control: Used in the pharmaceutical and chemical industries for quality control of raw materials and finished products.
  • Environmental analysis: Due to its ability to identify organic compounds it is used in monitoring air and water pollutants.

Example analysis - Aspirin

Consider the analysis of aspirin as a common example. Aspirin is another name for acetylsalicylic acid, which has the molecular formula C 9 H 8 O 4.

The IR spectrum of aspirin shows:

  • The strong peak at 1750 cm -1 represents the C=O stretching of the ester functional group.
  • The peak at 1680 cm -1 represents the C=O stretching of the carboxylic acid group.
  • The OH stretching absorption appears in the broad band around 2500-3000 cm -1.

Conclusion

Infrared spectroscopy is a valuable tool in organic chemistry that helps to identify functional groups and elucidate molecular structures. Its wide applications in various fields highlight its importance in both academic and industrial fields.

Custom question

  1. Explain the principle behind IR spectroscopy.
  2. Identify the functional groups present in the given IR spectrum: 
    Strong peaks at 1705 cm -1 and 3300 cm -1.
  3. What are the common sample preparation techniques in IR spectroscopy?
  4. Discuss the applications of IR spectroscopy in the pharmaceutical industry.

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Infrared Spectroscopy

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