NMR Spectroscopy: Videos & Practice Problems

How much do two signals differ in a 500 MHz spectrometer, if in a 400 MHz spectrometer they differ by 3.5 ppm?

Nuclear magnetic resonance (NMR) is a spectroscopic technique used to determine the structures of molecules in various universities and research centers. The technique involves placing a sample in a very strong magnetic field, generally produced by very large superconducting magnets, irradiating the sample with a radiofrequency, and recording the signal produced by the sample. However, the word "nuclear" might sound dangerous to a nonscientific listener and the NMR instrument might be misunderstood as a nuclear reactor producing nuclear waste. Assuming yourself as a researcher working with NMR, explain how the meaning of NMR can be conveyed to a layman or nonscientist.

a) NMR is a analytical technique while nuclear waste is related to nuclear reactions. 

b) By using NMR spectroscopy, we can generate frequencies that represent the chemical environment within a molecule in a magnetic field. Hazardous waste produced by nuclear reactions is nuclear waste. There are radioactive elements in it. NMR analysis generates no nuclear waste. 

c) Hazardous waste produced by nuclear reactions is nuclear waste. No reaction occurs during NMR analysis.

d) All of the above points collectively explain the fact. 

Determine if each of the following statements is true or false:

i. The coupling constant in hertz (Hz) is directly proportional to the operating frequency.

ii. Compared to the operating frequency in IR and UV-vis spectroscopy, the operating frequency in NMR spectroscopy is much higher.

Give the resonance frequencies of a carboxylic acid proton with a chemical shift of 10.5 ppm if it is detected using NMR spectrometers with the following operating frequencies:

i. 90 MHz

ii. 400 MHz

Determine the magnetic field strength necessary when a 750 MHz instrument for ¹H NMR is used. (γ for ¹H = 2.675 × 10⁸ T^-1s^-1) 

Determine the amount of energy (in calories) needed for an NMR spectrometer that works at 750 MHz to flip a ¹H nucleus.