NMR Flashcards
Which of the following best describes the principle behind Nuclear Magnetic Resonance (NMR)?
A. Detection of fluorescence from excited nuclei.
B. Interaction between atomic nuclei with nuclear spin and an external magnetic field.
C. Absorption of infrared light by vibrating molecular bonds.
D. Separation of isotopes by their boiling points.
B
Which factor contributes to differences in chemical shift in NMR spectroscopy?
A. Size of the molecule.
B. Speed of rotation around the nucleus.
C. Shielding effects caused by electrons around the nucleus.
D. Concentration of the sample in the solution.
C
What does the integration of a peak in
1 H NMR indicate?
A. The number of different types of protons in the molecule.
B. The number of protons represented by the peak.
C. The frequency of the applied magnetic field.
D. The type of functional group present in the molecule.
B
Which of the following describes the N + 1 rule in
1
𝐻
1
H NMR splitting patterns?
A. A peak splits into N + 1 peaks, where N is the number of neighboring hydrogens.
B. A peak forms N separate lines based on the number of carbon atoms present.
C. N + 1 refers to the number of protons in a single molecule being analyzed.
D. The rule applies only to nuclei with zero spin.
A
Which statement about chemical shift is TRUE?
A. Chemical shift is measured in frequency (Hz).
B. Protons in deshielded environments appear further upfield.
C. Chemical shift is measured in parts per million (ppm).
D. All protons have the same chemical shift in NMR.
C
In NMR, what is the function of heavy water (
𝐷2O) in hydroxyl/amine proton exchange experiments?
A. To create stronger coupling interactions between protons.
B. To exchange
1 H protons with H2, causing the OH or NH peak to disappear.
C. To enhance the magnetic field around the nucleus.
D. To prevent splitting of equivalent protons.
B
Which of the following is NOT a limitation of spin-spin coupling in NMR?
A. Coupling does not occur between equivalent protons.
B. Coupling does not occur across heteroatoms such as oxygen and nitrogen.
C. Coupling only occurs between protons with identical chemical shifts.
D. Coupling is symmetrical, with central peaks stronger than outer peaks.
C
In NMR-based drug discovery, what is a key advantage of combining HPLC with NMR (HPLC-NMR)?
A. It allows for the analysis of volatile compounds only.
B. It provides molecular weight determination through peak integration.
C. It enables identification and structural elucidation of components in complex mixtures.
D. It replaces the need for mass spectrometry in all analyses.
C
What does the chemical shift in 1H NMR tell you about a proton?
A. The total number of protons in the molecule.
B. The electronic environment surrounding the proton.
C. The number of bonds the proton is involved in.
D. The molecular weight of the compound.
B
What does the term “shielding” refer to in NMR spectroscopy?
A. Protection of the nucleus from an external magnetic field by surrounding electrons.
B. Reduction of signal intensity due to sample concentration.
C. Increased peak splitting due to neighboring protons.
D. Removal of solvent peaks through deuterated solvents.
A
In H NMR, what is the expected splitting pattern for a proton with two neighboring equivalent protons?
A. Singlet
B. Doublet
C. Triplet
D. Quartet
C
Which factor does NOT influence the intensity of an NMR signal?
A. Number of equivalent protons in the sample.
B. Molar concentration of the sample.
C. Applied external magnetic field strength.
D. Solvent viscosity.
D
Which solvent is commonly used in NMR because it lacks
1
𝐻
1
H protons?
A. WATER
B. Chloroform-d (CDCl 3 )
C. Ethanol
D. Acetone
B
Which statement about spin-spin coupling in NMR is TRUE?
A. Equivalent protons show strong coupling with each other.
B. The splitting pattern is determined by the number of adjacent protons using the N + 1 rule.
C. Coupling constants are measured in ppm.
D. Coupling is unaffected by the presence of heteroatoms like oxygen.
B
What causes the disappearance of an OH peak when
𝐷
2
𝑂
D
2
O is added to an NMR sample?
A. Hydroxyl protons are exchanged with deuterium, which is NMR-inactive in the H spectrum.
B. Hydroxyl protons form stronger bonds that broaden the peak.
C. Deuterium enhances the coupling effect, making the peak disappear.
D2O suppresses the magnetic field’s effect on hydroxyl protons.
A
