Lab 8. Prelab Questions.

Questions you NEED to answer in a written form (in your lab notebook) before the Lab. 

• Estimate the difference in populations between two nuclear spin orinetations m_I = +1/2 and m_I = -1/2 for a free proton at room temperature and T = 77 K in a magnetic field B₀ = 4T.
• Sketch the ¹H spectra of
  • ethanol
  • 2-propanol
  • benzene
  • acetone
  • 1,4 -hydroxybenzene (hydroquinone)
  • 1,2 - hydroxybenzene (cathecol)
  • perylene
• What will change and what will remain the same in these spectra when you use a 60 MHz or a 200 MHz spectrometers?
• You use a 200 MHz NMR spectrometer and observe two lines separated by 1 ppm. What is the frequency shift between them in Hz?
• You are asked to prepare 5 mL of acetate/acetic acid (pK_a = 4.75 @25°C) buffer at pH = 4.5 and adjust its ionic strength to 2M using NaCl; how do you proceed?

What kind of questions you MAY be asked before the Lab.

• What are the main components of an NMR spectrometer?
• Why is there a rush among scientists to get NMR spectrometers of higher and higher working frequencies? What is good and what is bad about it?
• Does the coalescence temperature for spin exchange depend on the frequency of your spectrometer?
• What is a magic spinning angle and why it helps?
• Can NMR of paramagnetic species be employed? What is a problem?
• What is a relaxation time? What is a difference between T₁ and T₂?

Last updated 03/22/99.
Email: snsm@nmsu.edu