Spectrometry

• What does NMR stand for?

  Nuclear Magnetic Resonance
• What is the basic principle of NMR?

  It uses a magnetic field and radio frequency waves to analyze the structures of complex molecules.
• How does NMR determine the state of nuclei?

  It monitors energy changes when nuclei flip from parallel to anti-parallel in a magnetic field.
• What is one use of NMR?

  MRI scans
• What kind of nuclei does NMR work with?

  Nuclei with an uneven number of nucleons, such as $^{1}H$ and $^{13}C$.
• What do the following terms mean for $^{13}C$ NMR: Number of signals, Chemical shift, Area under peak, Splitting?


  • Number of signals: One signal for each carbon environment (each set of inequivalent $^{13}C$ atoms)
  • Chemical shift: Greater shift indicates different electronic environments
  • Area under peak: Proportional to the number of equivalent $^{13}C$ atoms
  • Splitting: Indicates neighboring hydrogen atoms affecting the magnetic field
• Why is it easier to get a spectrum of $^{1}H$ NMR than $^{13}C$ NMR?


  Because $^{1}H$ is more abundant than $^{13}C$, leading to more signals.
• On a low resolution spectrum, what peaks would you expect to see for $^{1}H$ NMR?


  One peak for each set of inequivalent $^{1}H$ atoms.
• What does the area under the peak represent in $^{1}H$ NMR?


  It is proportional to the number of $^{1}H$ atoms represented by the peak.
• What is the integration trace?

  A stepped line that helps measure the area under the curve in NMR spectra.
• What is TMS and what does it stand for?

  Tetramethylsilane

  
• Why is TMS used in NMR?

  It calibrates the NMR equipment by providing a reference peak.
• What are other advantages of using TMS?

  It is inert, non-toxic, and easy to remove from the sample.
• When does splitting or spin-spin coupling occur in NMR?

  When neighboring hydrogen atoms affect the magnetic field of $^{1}H$ atoms.

  
• What is the n+1 rule in NMR?

  If there are n inequivalent $^{1}H$ atoms on the neighboring carbon, the peak will split into (n+1) smaller peaks.
• What are the splitting patterns for 0, 1, 2, and 3 inequivalent H atoms 3 bonds or less away?

  • 0 inequivalent H: 1 peak
  • 1 inequivalent H: 2 peaks
  • 2 inequivalent H: 3 peaks
  • 3 inequivalent H: 4 peaks
• Why must solvents used for $^{1}H$ NMR not contain any hydrogen atoms?


  Because signals from the solvent would overwhelm signals from the sample.
• Which solvents are commonly used for $^{1}H$ NMR?


  Deuterated solvents like CDCl₃, D₂O, and C₆D₆.
• What do the following terms indicate for $^{1}H$ NMR: Number of signals, Chemical shift, Splitting, Area under peak?


  • Number of signals: One main signal for each set of inequivalent $^{1}H$ atoms
  • Chemical shift: Larger shifts indicate different environments
  • Splitting: Indicates neighboring hydrogen atoms affecting the magnetic field
  • Area under peak: Proportional to the number of equivalent $^{1}H$ atoms
• Why does the peak from O-H bonds disappear if D₂O is used as a solvent?

  Because an O-D bond is formed instead of an O-H bond due to labile protons.