In this worksheet, we will practice generating an applied magnetic field and using an RF pulse to produce NMR spectra from spin-active nuclei.
Q1:
In a NMR experiment, an external magnetic field is applied to the sample. What happens to the protons in the sample?
- AAll protons align with the field.
- BAll protons align opposite to the field.
- CAll protons assume a random orientation.
- DSome protons align with the field and some align opposite to it.
Q2:
In a NMR experiment, a radio frequency (RF) signal is applied to the sample, in addition to the magnetic field. What happens to the spins of the sample?
- AThe RF will force all spins to assume a random orientation.
- BThe RF will force all spins to align opposite to the magnetic field.
- CThe RF will force all spins to align with the magnetic field.
- DThe RF will flip the spin, inducing a spin transition to a slightly higher-energy state.
Q3:
Which of the following molecular properties is affected by the measurement of an NMR spectrum?
- ACore electrons
- BValence electrons
- CMolecular vibrations
- DNuclear spin
- EMolecular rotations
Q4:
The electromagnetic radiation used for NMR spectroscopy falls in which region?
- AX-ray
- BMicrowave
- CGamma ray
- DRadio wave
- EUltraviolet
Q5:
In which units are NMR chemical shifts usually reported?
- A MHz
- B Hz
- C nm
- D ppm
Q6:
In NMR spectroscopy, what happens to the chemical shift and resonance frequency of a compound when the spectrometer frequency changes?
- AThe chemical shift changes; the resonance frequency remains constant.
- BThe chemical shift and resonance frequency also change.
- CThe chemical shift and resonance frequency remain constant.
- DThe chemical shift remains constant; the resonance frequency changes.
- EThere is no way to predict the effect.
Q7:
NMR involves what kind of analysis?
- AMagnetizing the molecules so they can be separated by traveling through a vacuum down a long tube surrounded by static magnets.
- BSpinning nuclei in such a way that they can be seen with infrared radiation and functional groups determined from the frequency.
- CUsing high energy beams to excite the electrons so they can be detected by magnetic field fluctuations.
- DUsing radio waves to detect nuclei present in a molecule (such as or ) and based on extensive data bases of “chemical shifts,” determine what each type is bonded to.