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


Spectroscopy is a powerful tool used to determine the structure of molecules in organic chemistry. It involves the interaction of matter with electromagnetic radiation to provide detailed information about molecular structure, dynamics, and environment. This field plays an essential role in chemistry by allowing scientists to understand the structure and quality of substances. Today, we will explore the different types of spectroscopy techniques commonly used in organic chemistry and how they aid in structural determination.

Types of spectroscopy

Infrared spectroscopy (IR)

Infrared spectroscopy involves the absorption of infrared light by a molecule, causing a change in vibrational energy levels. This helps to identify functional groups in a molecule as different bonds absorb different wavelengths.

Functional groups such as -OH, -NH, and -CH can be easily identified.
4000 400 IR Spectrum

An example of using IR spectroscopy is to identify the carbonyl group (C=O), which typically shows a strong peak around 1700 cm-1.

Ultraviolet-visible spectroscopy (UV-Vis)

UV-Vis spectroscopy involves the absorption of ultraviolet or visible light by electrons in a molecule, which can cause electronic transitions. This type of spectroscopy is useful in studying conjugated systems and compounds with pi-electrons.

For example, UV-Vis can analyze conjugated dienes and aromatic compounds.
200 800 UV-Vis spectrum

Benzene exhibits a characteristic absorption peak in the UV region due to the pi to pi* transition.

Nuclear magnetic resonance (NMR) spectroscopy

NMR spectroscopy is one of the most powerful techniques for structural determination in organic chemistry. This method uses the magnetic properties of certain nuclei. When placed in a magnetic field, these nuclei absorb radiation at specific frequencies depending on their electronic environment.

The common nuclei analyzed are 1H and 13C.

1H NMR: Provides information about the hydrogen atoms in an organic molecule.

1 10 NMR Spectrum

Each peak indicates a hydrogen atmosphere, with chemical shifts varying depending on neighboring atoms and electron cloud density.

Structural determination methods

Structural determination in organic chemistry is dependent on the detailed analysis provided by various spectroscopic methods. Once the spectra are obtained, interpretation is important to predict the structure.

Interpretation of IR spectra

In the IR spectrum, the position and intensity of the peaks provide information about the functional groups present. When analyzing the IR spectrum, consider the following steps:

  1. Identify the characteristic strong, broad peaks of OH extension in alcohols and phenols that typically occur between 3300-3500 cm-1.
  2. Observe sharp peaks between 1600-1700 cm-1, which indicate C=O stretching.
  3. Compare the intensity of the peaks to known standards or reference spectra.

Interpretation of UV-Vis spectra

UV-Vis spectra involve the analysis of absorption peaks related to electronic transitions. Knowing the basics of the spectrum helps:

  • Understand the maximum λ (lambda max) values, which indicate electronic excitations.
  • Relate the absorption intensity to the electronic transition probability - more extended conjugation usually leads to higher wavelength absorption.

Interpretation of NMR spectra

NMR spectra require the analysis of chemical shifts, integration, and coupling patterns:

  1. Chemical shift: Reflects the environment of the absorbing nucleus. The more the proton is depolarized (usually by electronegative atoms), the higher the chemical shift.
  2. Integration: The area under the NMR peak is proportional to the number of hydrogens present in it.
  3. Partition pattern: Provides information about neighboring hydrogens through the n+1 rule, where n is the number of adjacent hydrogens.

Examples of structural explanations

For a structural explanation consider a simple molecule such as ethanol (C2H5OH).

Use of IR spectroscopy for ethanol

C2H5OH IR Spectrum:
  • Typical broad peak around 3300 cm-1 due to OH stretching.
  • Intense peak near 2900 cm-1 due to CH stretching.

Use of NMR spectroscopy for ethanol

1H NMR spectrum:
  • Triplet of about 1.2 ppm for CH3 group - splitting by two adjacent protons (n+1 rule).
  • The quartet for the CH2 group is about 3.6 ppm - splitting by three adjacent protons.
  • Singlet around 5.0 ppm for the OH proton.

By combining insights gained from IR, NMR, and UV-Vis spectroscopy, chemists can predict molecular structure and confirm the presence of particular functional groups within a given compound.

Conclusion

Spectroscopy and structural determination are fundamental techniques in organic chemistry. Detailed investigation of spectra enables chemists to unravel the molecular complexities of substances. As techniques advance, these methods become more sophisticated and precise, making them indispensable tools not only in academic research but also in the pharmaceutical and chemical industries where understanding molecular structure is crucial.

Understanding and mastering these techniques requires diligent study and practice, but they bring the exciting possibility of unraveling the mysteries of molecular architecture.


Graduate → 2.2


U
username
0%
completed in Graduate

← Prev (2.1.6)
Pericyclic reactions
Next (2.2.1) →
UV-Vis Spectroscopy

Comments 



Spectroscopy and structural determination

https://www.chemistryelite.com/g/2.2?ceal=en