Glossary
Practice Quizzes

13.1 Nuclear Magnetic Resonance Spectroscopy

2 min read•may 7, 2024

uses atomic properties to analyze molecules. When placed in a magnetic field, certain nuclei align and precess at specific frequencies, revealing structural information about compounds.

NMR exploits the energy difference between spin states to generate spectra. The strength of the applied magnetic field and the nature of the nuclei determine the energy gap and resulting signal frequencies, enabling detailed molecular analysis.

Nuclear Magnetic Resonance (NMR) Spectroscopy

Nuclear spin-magnetic field interaction

Top images from around the web for Nuclear spin-magnetic field interaction

  • A quantum spectrum analyzer enhanced by a nuclear spin memory | npj Quantum Information View original

    Is this image relevant?

  • One-second coherence for a single electron spin coupled to a multi-qubit nuclear-spin ... View original

    Is this image relevant?

  • A quantum spectrum analyzer enhanced by a nuclear spin memory | npj Quantum Information View original

    Is this image relevant?

1 of 3

Top images from around the web for Nuclear spin-magnetic field interaction

  • A quantum spectrum analyzer enhanced by a nuclear spin memory | npj Quantum Information View original

    Is this image relevant?

  • One-second coherence for a single electron spin coupled to a multi-qubit nuclear-spin ... View original

    Is this image relevant?

  • A quantum spectrum analyzer enhanced by a nuclear spin memory | npj Quantum Information View original

    Is this image relevant?

1 of 3
  • Atomic nuclei possessing odd number of protons and/or neutrons exhibit (1H, 13C, 15N, 19F, 31P)
    • Spin is intrinsic angular momentum of nucleus visualized as spinning motion
  • Without external magnetic field, spins orient randomly
  • In presence of external magnetic field (B0B_0), spins align parallel or antiparallel to field
    • Parallel alignment is lower energy α\alpha state, antiparallel is higher energy β\beta state
    • Energy difference between α\alpha and β\beta states directly proportional to B0B_0 strength
  • Spins precess around B0B_0 axis at
    • Larmor frequency depends on B0B_0 strength and of nucleus (1H, 13C)

Magnetic strength and spin transition energy

  • Energy difference (ΔE\Delta E) between α\alpha and β\beta spin states given by:
    • ΔE=hγB02π\Delta E = \frac{h \gamma B_0}{2\pi}
      • hh: Planck's constant
      • γ\gamma: gyromagnetic ratio, nucleus-specific constant (1H, 13C)
      • B0B_0: external magnetic field strength
  • Stronger B0B_0 increases ΔE\Delta E between α\alpha and β\beta states
  • Spin state transition requires electromagnetic radiation at Larmor frequency
    • Radiation energy must equal ΔE\Delta E between spin states
  • Frequency (ν\nu) of radiation for transition:
    • ν=γB02π\nu = \frac{\gamma B_0}{2\pi}
      • ν\nu: electromagnetic radiation frequency
      • γ\gamma, B0B_0: as defined above (1H, 13C)

NMR behavior vs nuclear composition

  • Even number of protons and neutrons: no net spin, NMR inactive (12C, 16O, 32S)
  • Odd number of protons and/or neutrons: net spin, NMR active
    • (II) depends on unpaired protons and neutrons
    • Odd mass number (odd total protons + neutrons): half-integer II (1/2, 3/2, 5/2)
      • 1H (I=1/2I = 1/2), 13C (I=1/2I = 1/2), 19F (I=1/2I = 1/2)
    • Even mass number, odd protons and neutrons: integer II (1, 2, 3)
      • 2H (I=1I = 1), 14N (I=1I = 1)
  • Gyromagnetic ratio (γ\gamma) varies among nuclei
    • Higher γ\gamma: more NMR sensitive, lower B0B_0 needed for given Larmor frequency
    • 1H has highest γ\gamma among common NMR-active nuclei, most sensitive for NMR spectroscopy
  • affects the local magnetic field experienced by nuclei, leading to

Advanced NMR Techniques

  • : Uses short radiofrequency pulses to excite all nuclei simultaneously
  • : The time-domain signal produced after a pulse, which is Fourier transformed to obtain the frequency-domain spectrum
  • : Through-space dipolar coupling between nuclei, used to determine spatial relationships in molecules
  • (MRI): Application of NMR principles for non-invasive medical imaging of soft tissues

Key Terms to Review (32)

Bloch: Bloch is a fundamental concept in nuclear magnetic resonance (NMR) spectroscopy, named after the Swiss physicist Felix Bloch. It describes the behavior of nuclear spins within a magnetic field and forms the basis for understanding the principles of NMR, a powerful analytical technique used in chemistry and other scientific fields.
Chemical Environment: The chemical environment refers to the specific set of conditions, including the presence and concentration of various atoms, molecules, and ions, that surround a particular chemical species or compound. This term is particularly important in the context of nuclear magnetic resonance (NMR) spectroscopy, as the chemical environment of a nucleus directly affects its observed signal or 'chemical shift'.
Chemical shift: In nuclear magnetic resonance (NMR) spectroscopy, a chemical shift is a measure of the change in the resonant frequency of a nucleus relative to a standard reference. It provides insights into the electronic environment surrounding a nucleus, helping to identify molecular structures.
Chemical Shift: Chemical shift is a fundamental concept in nuclear magnetic resonance (NMR) spectroscopy that describes the position of a signal in the NMR spectrum relative to a reference signal. It provides information about the chemical environment of a nucleus, allowing for the identification and characterization of different functional groups and molecular structures.
COSY: COSY, short for Correlated Spectroscopy, is a two-dimensional nuclear magnetic resonance (NMR) technique used to identify the connectivity between protons (hydrogen atoms) within a molecule. It is a powerful tool for elucidating the structure of organic compounds by providing information about the spatial relationships between different hydrogen atoms.
DEPT–NMR: DEPT-13C NMR Spectroscopy is a specialized technique used in organic chemistry to differentiate carbon atoms based on the number of hydrogen atoms attached to them. It provides detailed information about the molecular structure by producing spectra that indicate whether carbon atoms are connected to zero, one, two, or three hydrogen atoms.
Deuterated Solvent: A deuterated solvent is a solvent in which one or more of the hydrogen atoms have been replaced with deuterium, a stable isotope of hydrogen. These solvents are commonly used in nuclear magnetic resonance (NMR) spectroscopy to provide a background signal that does not interfere with the signals from the analyte of interest.
Fourier Transform: The Fourier transform is a mathematical operation that decomposes a function or signal into its constituent frequencies. It is a fundamental tool in the analysis and interpretation of nuclear magnetic resonance (NMR) spectroscopy, as it allows the conversion of time-domain signals into frequency-domain spectra.
Free Induction Decay: Free Induction Decay (FID) is a fundamental concept in Nuclear Magnetic Resonance (NMR) spectroscopy, which is a powerful analytical technique used to study the structure and dynamics of molecules. FID describes the oscillating signal that is detected in an NMR experiment after the sample is exposed to a strong magnetic field and a radiofrequency (RF) pulse.
FT–NMR: FT-NMR (Fourier Transform Nuclear Magnetic Resonance) is a technique used in organic chemistry to determine the molecular structure of organic compounds by observing the interaction of nuclear spins when placed in a magnetic field and radiated with radiofrequency. This process transforms the time-domain NMR signal into a frequency-domain spectrum, providing detailed information about the chemical environment of the nuclei.
Gyromagnetic Ratio: The gyromagnetic ratio, also known as the magnetogyric ratio, is a fundamental physical constant that describes the relationship between the magnetic moment and the angular momentum of a particle or nucleus. It is a crucial parameter in the field of Nuclear Magnetic Resonance (NMR) Spectroscopy and is directly related to the chemical shift observed in NMR experiments.
HSQC: HSQC, or Heteronuclear Single Quantum Coherence, is a two-dimensional nuclear magnetic resonance (NMR) spectroscopic technique that provides information about the direct one-bond correlation between hydrogen (1H) and carbon (13C) nuclei in organic molecules. It is a powerful tool used in the analysis and structural elucidation of organic compounds.
J-Coupling: J-coupling, also known as spin-spin coupling, is a phenomenon observed in nuclear magnetic resonance (NMR) spectroscopy where the magnetic moments of neighboring nuclei interact, resulting in the splitting of NMR signals. This interaction provides valuable information about the chemical structure and connectivity of molecules.
Larmor Frequency: Larmor frequency, also known as the nuclear precession frequency, is a fundamental concept in nuclear magnetic resonance (NMR) spectroscopy. It describes the rate at which the magnetic moments of nuclei, such as hydrogen (1H) or carbon (13C), precess or rotate around an applied magnetic field.
Magnetic Resonance Imaging: Magnetic resonance imaging (MRI) is a non-invasive imaging technique that uses strong magnetic fields and radio waves to generate detailed images of the body's internal structures. It is a powerful diagnostic tool that allows healthcare professionals to visualize and assess various organs, tissues, and pathologies without the use of ionizing radiation.
Magnetogyric ratio: The magnetogyric ratio is a physical constant that quantifies the relationship between the magnetic moment and angular momentum of a nucleus. It plays a crucial role in determining the resonance frequency of nuclei in a magnetic field during Nuclear Magnetic Resonance (NMR) spectroscopy.
Multiplicity: Multiplicity in the context of nuclear magnetic resonance (NMR) spectroscopy refers to the splitting pattern observed in the signal of a proton (1H) or other nucleus due to the magnetic interactions between the nucleus and the surrounding hydrogen atoms. This splitting pattern provides valuable information about the structure and environment of the molecule being analyzed.
NOE: NOE, or Nuclear Overhauser Effect, is a phenomenon observed in nuclear magnetic resonance (NMR) spectroscopy that arises from the dipole-dipole interactions between nearby nuclear spins. It provides valuable information about the spatial proximity of protons within a molecule, allowing for the determination of molecular structure and conformation.
NOESY: NOESY, or Nuclear Overhauser Effect Spectroscopy, is a two-dimensional NMR technique used to determine the spatial proximity of hydrogen atoms within a molecule. It provides information about the through-space interactions between nearby protons, allowing for the elucidation of molecular structure and conformation.
Nuclear Magnetic Resonance Spectroscopy: Nuclear Magnetic Resonance (NMR) Spectroscopy is an analytical technique that uses the magnetic properties of certain atomic nuclei to determine the structure and composition of organic compounds. It is a powerful tool for identifying and characterizing the chemical environment of specific atoms within a molecule.
Nuclear Overhauser Effect: The nuclear Overhauser effect (NOE) is a phenomenon in nuclear magnetic resonance (NMR) spectroscopy where the intensity of an NMR signal is influenced by the presence of nearby nuclear spins. It is a valuable tool for understanding the three-dimensional structure of molecules and the interactions between them.
Probe: A probe is a device or instrument used to investigate or examine something, often in the context of scientific research or medical procedures. In the realm of nuclear magnetic resonance (NMR) spectroscopy, a probe is a critical component that plays a crucial role in the acquisition and analysis of NMR data.
Pulsed NMR: Pulsed NMR is a technique used in nuclear magnetic resonance (NMR) spectroscopy that involves the application of short, high-intensity radio frequency (RF) pulses to excite the nuclear spins in a sample. This method is particularly important in the context of 13C NMR spectroscopy, as it enables the efficient acquisition of 13C NMR spectra.
Purcell: Purcell is a fundamental concept in the field of Nuclear Magnetic Resonance (NMR) Spectroscopy, which is a powerful analytical technique used to study the structure and properties of molecules. Purcell's work laid the groundwork for the development of modern NMR spectroscopy, making significant contributions to the understanding of nuclear magnetic phenomena.
Relaxation: Relaxation is the process by which a system or object returns to its equilibrium state after being perturbed. In the context of Nuclear Magnetic Resonance (NMR) spectroscopy, relaxation describes how nuclear spins interact with their surrounding environment, allowing the absorption and emission of energy to be detected and analyzed.
Shielding: Shielding is a phenomenon that occurs in nuclear magnetic resonance (NMR) spectroscopy, where the applied magnetic field interacts with the electrons surrounding a nucleus, altering the effective magnetic field experienced by that nucleus. This shielding effect influences the chemical shift, a crucial parameter in NMR analysis.
Spectrometer: A spectrometer is an instrument used to measure and analyze the spectrum of electromagnetic radiation, such as light or other forms of energy. It is a crucial tool in various scientific fields, including chemistry, physics, and astronomy, as it provides valuable information about the composition and properties of materials.
Spin: Spin is a fundamental property of subatomic particles, such as electrons and nuclei, that describes their intrinsic angular momentum. It is a quantum mechanical concept that plays a crucial role in the understanding and interpretation of Nuclear Magnetic Resonance Spectroscopy (NMR).
Spin Angular Momentum: Spin angular momentum is a fundamental property of subatomic particles, such as electrons, protons, and neutrons, which describes their intrinsic angular momentum. It is a crucial concept in the field of quantum mechanics and is closely related to the phenomenon of nuclear magnetic resonance (NMR) spectroscopy.
Spin Quantum Number: The spin quantum number is a fundamental property of subatomic particles, such as electrons, that describes their intrinsic angular momentum or 'spin'. It is a crucial concept in understanding the behavior of particles in nuclear magnetic resonance (NMR) spectroscopy, a widely used analytical technique in organic chemistry.
Spin-Spin Coupling: Spin-spin coupling, also known as J-coupling, is a phenomenon in nuclear magnetic resonance (NMR) spectroscopy where the magnetic moments of adjacent nuclei interact with each other, leading to the splitting of NMR signals. This interaction provides valuable information about the structure and connectivity of molecules.
Tetramethylsilane: Tetramethylsilane (TMS) is a colorless, volatile liquid compound with the chemical formula Si(CH3)4. It is widely used as a standard reference compound in nuclear magnetic resonance (NMR) spectroscopy due to its unique properties that make it an ideal internal standard for 1H and 13C NMR experiments.
© 2024 Fiveable Inc. All rights reserved.
AP® and SAT® are trademarks registered by the College Board, which is not affiliated with, and does not endorse this website.
Back
Glossary
Glossary
13.2 The Nature of NMR Absorptions