3.3.15.1 Principles of NMR

• Steps involved in NMR spectroscopy

  1️⃣ Place the sample in a strong magnetic field

  2️⃣ Apply a radio frequency pulse

  3️⃣ Nuclei absorb energy at their natural frequency

  4️⃣ The absorbed energy is re-emitted

  5️⃣ The frequency of the radiation is measured

  6️⃣ The structure of the compound is determined
• Match the features with the correct type of NMR:

  $^{1}H$ NMR ↔️ Identifies hydrogen environments

  $^{13}C$ NMR ↔️ Identifies carbon environments
• Why is $^{1}H$ NMR more sensitive than ^{13}C</latex> NMR?


  High natural abundance of $^{1}H$
• $^{13}C$ NMR has a lower sensitivity
• What does Nuclear Magnetic Resonance (NMR) use to determine the structure of organic compounds?

  Magnetic properties of nuclei
• In NMR spectroscopy, a strong external magnetic field aligns the magnetic moments of nuclei.


  True
• When placed in an external magnetic field, nuclei align either parallel or anti-parallel
• What is the key process in NMR spectroscopy that allows for structural determination?

  Resonance absorption
• The frequency of radiation emitted by nuclei in NMR is unique to each type of nucleus.


  True
• $^{1}H$ NMR has a higher natural abundance than ^{13}C</latex> NMR.


  True
• Why is $^{1}H$ NMR more sensitive than $^{13}C$ NMR?


  High abundance and magnetic moment
• What is chemical shift measured in?

  Parts per million (ppm)
• What do integration values in an NMR spectrum indicate?

  Relative number of protons
• In NMR spectroscopy, a strong external magnetic field aligns the magnetic moments of nuclei.
• What type of nuclei are observed in $^{1}H$ NMR?


  Hydrogen atoms
• What is the chemical shift range in $^{1}H$ NMR?


  0-10 ppm
• $^{1}H$ NMR is used to identify proton environments and determine hydrogen connectivity.


  True
• The chemical shift range in $^{13}C$ NMR is 0-220 ppm
• The chemical shift depends on the electronic environment
• In the $^{1}H$ NMR spectrum of ethanol, the methyl group (-CH₃) has an integration value of 3
• The splitting pattern in NMR follows the n+1 rule
• Coupling constants are measured in Hertz
• The chemical shift range for alkanes in $^{1}H$ NMR is 0.5-1.5 ppm.
• What is the primary purpose of Nuclear Magnetic Resonance (NMR) spectroscopy?

  Determine structure of compounds
• What is the condition for resonance absorption in NMR spectroscopy?

  Pulse frequency matches natural frequency
• The signal strength in ^{1}H</latex> NMR is stronger than in $^{13}C$ NMR.


  True
• What is the typical appearance of peaks in $^{1}H$ NMR?


  Sharp peaks
• What is the natural abundance of $^{13}C$?


  1.1%
• What does the chemical shift measure in NMR spectra?

  Resonant frequency
• What do integration values in $^{1}H$ NMR spectra indicate?


  Relative number of protons
• What causes the splitting of signals in NMR spectra?

  Spin-spin coupling
• What information do splitting patterns reveal in NMR spectra?

  Connectivity and environment
• What do ^1JCH coupling constants indicate?

  Directly bonded C-H
• NMR works by placing a sample in a strong magnetic field
• What property do atomic nuclei with an odd number of protons and/or neutrons possess?

  Magnetic moment
• The parallel alignment of nuclei in a magnetic field is lower in energy and more populated.


  True
• Resonance absorption occurs when the frequency of the radio frequency pulse matches the natural frequency
• What happens to nuclei during resonance absorption when they absorb energy from a radio frequency pulse?

  They transition to a higher energy level
• $^{1}H$ NMR is more sensitive
• ^{1}H</latex> NMR has a natural abundance of approximately 99.98%.


  True