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 → Physical Chemistry → Spectroscopy ↓


Nuclear magnetic resonance spectroscopy


Nuclear magnetic resonance (NMR) spectroscopy is a powerful analytical technique used in physical chemistry to determine the structure of molecules. It works based on the magnetic properties of certain nuclei. NMR spectroscopy is particularly useful because it provides detailed information about the structure, dynamics, reaction state, and chemical environment of molecules.

Fundamentals of NMR

NMR relies on the magnetic properties of atomic nuclei. Not all nuclei are suitable for NMR analysis; they must have a property called spin. Nuclei with odd atomic or mass numbers have a net nuclear spin, which gives rise to a magnetic moment. The most common nuclei studied by NMR are ^{1}H and ^{13}C

B₀ Spin Direction

Nuclei with spin in a magnetic field (B₀)

The concept of spin

The concept of nuclear spin is central to NMR. Spin is a quantum mechanical property, and for NMR, we describe it using terms such as spin quantum number. Nuclei with a spin quantum number (I) such as ^{1}H (I = 1/2) have a magnetic moment due to their spin.

In the absence of an external magnetic field, the magnetic moments are randomly oriented. Upon the application of a magnetic field (denoted as B₀), these magnetic moments align either parallel or opposite to the field. The parallel alignment is the lower energy state, while the opposite direction is the higher energy state.

Resonance condition

When nuclei are exposed to electromagnetic radiation at a frequency specific to their magnetic environment, they can absorb energy and flip between energy states. This is known as a resonance state and it produces a detectable NMR signal. The frequency at which this occurs is known as the Larmor frequency.

Low Energy high energy Transitional Frequency

Energy Level Transitions in NMR

Interpretation of NMR spectra

NMR spectra provide several important information about molecular structure:

  • Chemical shift: Position on the spectral chart. It tells us about the electronic environment of the nucleus.
  • Multiplicity: splitting of signals, reflecting interactions between nuclei.
  • Integration: The area under the peaks indicates the number of nuclei.

Chemical shifts: Chemical shifts are observed as peaks in the spectrum and are measured in parts per million (ppm). They reveal the environment around the nucleus by indicating electronic shielding or de-shielding effects.

Example:
- The proton attached to the carbon adjacent to an electronegative atom like oxygen will be deprotected and shifted downwards (higher ppm).
- Aromatic protons resonate lower than aliphatic protons.

J-coupling and spin-spin splitting

Spin-spin coupling between nuclei results in the NMR signal being split into multiple peaks, called "multiplets." This splitting or coupling is quantified using the J-coupling constant, measured in hertz (Hz).

Example:
- The peaks may split into doublets, triplets, etc. due to interactions between protons on adjacent carbon atoms in the molecule.
- For example, consider ethyl alcohol: the methyl protons can appear as a triplet due to the neighboring group of the two methylene protons.
copy Trika Quartet

Illustration of multiple peaks due to J-coupling

NMR spectrometers and techniques

The NMR spectrometer consists of a powerful magnet, a radiofrequency (RF) transmitter and receiver, and a computer to analyze the data. The sample is placed in a magnetic field, and RF pulses are applied. The resulting signals are detected and used to create an NMR spectrum.

In modern NMR, the Fourier transform (FT-NMR) method is used to convert time-domain signals into frequency-domain spectra, which is faster and more accurate than the earlier continuous-wave method.

Applications of NMR spectroscopy

NMR is used in chemistry, biochemistry, medicine, and physics. Some applications include:

  • Structural elucidation: Determination of the structure of organic compounds.
  • Dynamic studies: Observing molecular motions and interactions.
  • Quantitative analysis: measuring concentrations in mixtures.
  • Medical diagnosis: MRI Imaging in the Medical Field.
Example:
- To determine the three-dimensional structure of proteins in solution.
- Investigating carbohydrate metabolism via natural abundance 13C NMR.

Advanced NMR techniques

Several advanced NMR techniques have been developed:

  • 2D NMR: Provides information on correlations between nuclei, e.g., COSY, HSQC, and NOESY.
  • Solid state NMR: used to study molecules in solid forms.
  • High-resolution magic angle spinning (HRMAS): Useful for samples with both solid and liquid properties.

These techniques extend the ability of NMR to study complex systems such as membranes, solids, and large biomolecules.

Conclusion

Nuclear magnetic resonance spectroscopy is a versatile and valuable tool in modern chemistry and related fields. Its ability to provide detailed information about molecular structure and dynamics is unmatched by other analytical methods. With continued technological advances, its range of applications continues to expand, providing insights into increasingly complex molecular systems.


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Nuclear magnetic resonance spectroscopy

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