University of Florida CHM 2210 Nuclear Magnetic Resonance
Spectroscopy || Questions and Answers.
nuclear magnetic resonance (NMR) spectroscopy correct answers the most powerful tool for
characterizing organic molecules, because it can be used to identify the carbon-hydrogen
framework.
2 common types of NMR correct answers 1H NMR (proton NMR) is used to determine the
number and type of hydrogen atoms present in a molecule.
13C NMR (carbon NMR) is used to determine the type of carbon atoms in a molecule.
The Basis of NMR correct answers - source of energy is radio waves
- when these low energy radio waves interact with a molecule, they can change the nuclear s[oms
pf some elements, including 1H and 13C.
In a magnetic field, there are now two different energy states for a proton:
- a lower energy state with the nucleus aligned in the same direction as B.
- a higher energy state with the nucleus aligned opposed to B.
When an external energy source (hv) that matches the energy difference between these two states
is applied, energy is absorbed, causing the nucleus to "spin flip" from one orientation to another.
When is a nucleus in resonance? correct answers when it absorbs RF radiation and "spin flips" to
a higher energy state.
What two variables characterize NMR? correct answers - an applied magnetic field, B
- The frequency v of radiation used for resonance
, the frequency needed for resonance and the applied magnetic field strength are proportionally
related.
the stronger the magnetic field, the larger the energy difference between the two nuclear spin
states, and the higher the v needed for resonance.
Do all protons absorb at the same frequency? correct answers No. All protons do not absorb at
the same frequency. Protons in different environments absorb at slightly different frequencies,
and so they are distinguishable by NMR.
Only nuclei that contain odd mass numbers or odd atomic numbers give rise to NMR signals.
What does an NMR spectrum plot? correct answers the intensity of a signal against its chemical
shift measured in parts per million.
Important NMR features correct answers - NMR absorptions generally appear as sharp signals
- increased chemical shift is plotted from right to left
- the terms upfield and downfield describe the relative location of signals.
- upfield means to the right
- downfield means to the left
- NMR absorptions are measured relative to the position of a reference signal at 0 ppm.
What is the reference signal? correct answers tetramethylsilate (TMS) is a volatile and inert
compound that gives a single peak upfield from other typical NMR absorptions.
Spectroscopy || Questions and Answers.
nuclear magnetic resonance (NMR) spectroscopy correct answers the most powerful tool for
characterizing organic molecules, because it can be used to identify the carbon-hydrogen
framework.
2 common types of NMR correct answers 1H NMR (proton NMR) is used to determine the
number and type of hydrogen atoms present in a molecule.
13C NMR (carbon NMR) is used to determine the type of carbon atoms in a molecule.
The Basis of NMR correct answers - source of energy is radio waves
- when these low energy radio waves interact with a molecule, they can change the nuclear s[oms
pf some elements, including 1H and 13C.
In a magnetic field, there are now two different energy states for a proton:
- a lower energy state with the nucleus aligned in the same direction as B.
- a higher energy state with the nucleus aligned opposed to B.
When an external energy source (hv) that matches the energy difference between these two states
is applied, energy is absorbed, causing the nucleus to "spin flip" from one orientation to another.
When is a nucleus in resonance? correct answers when it absorbs RF radiation and "spin flips" to
a higher energy state.
What two variables characterize NMR? correct answers - an applied magnetic field, B
- The frequency v of radiation used for resonance
, the frequency needed for resonance and the applied magnetic field strength are proportionally
related.
the stronger the magnetic field, the larger the energy difference between the two nuclear spin
states, and the higher the v needed for resonance.
Do all protons absorb at the same frequency? correct answers No. All protons do not absorb at
the same frequency. Protons in different environments absorb at slightly different frequencies,
and so they are distinguishable by NMR.
Only nuclei that contain odd mass numbers or odd atomic numbers give rise to NMR signals.
What does an NMR spectrum plot? correct answers the intensity of a signal against its chemical
shift measured in parts per million.
Important NMR features correct answers - NMR absorptions generally appear as sharp signals
- increased chemical shift is plotted from right to left
- the terms upfield and downfield describe the relative location of signals.
- upfield means to the right
- downfield means to the left
- NMR absorptions are measured relative to the position of a reference signal at 0 ppm.
What is the reference signal? correct answers tetramethylsilate (TMS) is a volatile and inert
compound that gives a single peak upfield from other typical NMR absorptions.
