NMR Flashcards
Forklar lidt om Heteronucleaer og
Hvilke nuclei
Hvilke bindinger
Hvilke spektre
Heteronucleaer:
Forskellige nuclei på hver akse
- HSQC : 1 bond coupling (1J)
- HMQC: 1 bond coupling (1J)
HMBC: 2J, 3J, 4J
DEPT 145
DEPT 90
DETP 135
APT
145: CH, CH2, CH3
90: CH
135: CH3, CH, - CH2,
APT: CH3, CH, -CH2, -C
EXSY
hvad står det for?
hvordan laves correlation?
Evolution: EXSY (Exchange spektroscopy)
Preparation time, evolution time, mixing, aquisition time
Summen af de exchanges, 50 % * og 50 % trekant
Chemal exchange for kunne lave correlation.
What sort of information do you obtain from a DOSY spectrum?
ppm vs. diffusion constant
What sort of information do you obtain from a TOCSY spectrum?
total correlation spectroscopy, cross peaks between atoms by an uninterupted chain of J3 or J4.
- What is T2-relaxation? also called
- What does it depend on?
- How does it manifest itself in NMR spectra?
- The decay of transverse magnetization without reestablishment of equilibrium
tranverse or spin-spin relaxation
- Magnetic Field Strength
- T2 relaxation leads to line broadening in the NMR spectra, The faster the T2, the broader the lines.
- What is T1-relaxation? what is it also called
- Explain when it occurs, what happens during the process, what does its speed depend on?
- When do you have to take T1-relaxation into account during planning of your experiment?
After excitation of nuclear magnetic spins, the distribution of nuclear magnetic moments in space reverts back to its equillibrium distribution.
also called “longitudinal” or “spin lattice” relaxation
- Happens after RF pulse, depends on strength of the magnetic field.
- Recovery Time between Pulses, Signal Intensity
sensitivity is expressed as ..
signal to noise ratio
Which information do you obtain from an HMBC spectrum?
J2, J3, J4
Describe the role of the field-frequency lock!
How does it work? Why is it necessary (how would NMR spectra look like if there were no field-frequency lock)?
ensure stability and accuracy of the magnetic field during NMR experiments.
The lock system constantly monitors the resonance frequency of the solvent 2H signal and keeps the field constant
NMR uden lock:
NMR spectra would be distorted, with peak positions shifting and signal intensities varying unpredictably. making it challenging to interpret the spectral information
What is “sensitivity” in NMR?
What does it depend on and how can it be improved?
The quality of a spectrum is defined mainly by the sensitivity and the resolution.
Can be improved by a higher sample concentration, increased number of scans, higher field strength, multiplication of the FID.
What are pulsed field gradients and what can they be used for?
lineære inhomogene fields,
By applying a gradient, molecules experience different magnetic environments, leading to variations in the acquired NMR signal.
bruges til:
variations in the resonance frequencies
study of molecular dynamics
Which of below particle(s) can have spin?
all elementary particles (proton, neutron and electron) have a spin ½.
Nuclei CAN(!) have spin. Atoms CAN(!) have spin, but they are not elementary particles.
All atomic nuclei with a spin … have angular momentum
All atomic nuclei with a spin I > 0 have angular momentum
A spin echo is a pulse element consisting of a x, followed by a x, followed by a x. Its purpose is to refocus chemical shift evolution. It also refocusses heteronuclear coupling.
delay, 180 pulse, delay
Why are NMR magnets immersed in liquid helium?
Most NMR magnets are superconducting and have to be cooled by liquid helium
Scalar coupling between two spins separated by four bonds is called…. → …,
Scalar coupling between two spins separated by two bonds is called…. → … ,
Scalar coupling between two spins separated by three bonds is called…. → …
The correct answer is: Scalar coupling between two spins separated by four bonds is called…. → … allylic coupling, Scalar coupling between two spins separated by two bonds is called…. → … geminal coupling, Scalar coupling between two spins separated by three bonds is called…. → … vicinal coupling
What does the abbreviation “NOE” stand for?
What can the NOE be used for?
What does the magnitude of the NOE depend on?
What does the abbreviation “NOE” stand for?
Nuclear overhauser effect, NOE, describes the observation that the signal of one nucleus changes its intensity, if nearby nucleus is saturated.
What can the NOE be used for?
13C-NMR spectra are routiningly recorded with 1H saturation to increase signal strength
What does the magnitude of the NOE depend on?
The changes in intensity depends on the gyromagnetic ratios of the saturated and observed nuclei as well as on molecular mobility.
Which information does a ROESY spectrum contain? Which experiment can give you the same information (most of the times)? When do you have to use the ROESY?
Which information does a ROESY spectrum contain? :
homonuclaer through space
kan estimere afstand mellem atomer, godt til at finde molekyle struktur + stereokemi.
oftest H-H men kan også andre nuklei.
5Å , dipolar copuling
cross beaks between 2 H atoms if they are closer than 5 Å in space.
Which experiment can give you the same information (most of the times)?:
NOESY og ROESY er næsten de samme.
When do you have to use the ROESY?:
skal bruge ROESY til at se vand: NOESU giver ikke cross peaks for molekyler der er 1-2kDa , ROESY laver cross peaks for alle molekylære masser.
HSQC
HMQC
HSQC : hetero single quantum coherence, J1
HMQC : hetero multiple quantum coherence, HMBC: giver long-range H-C koblinger (over 2-4 bindinger)
INADEQUATE: giver 13C-13C korrelationer (kræver godt nok enorme mængder materiale)
magnitization can tranferes by 3 things
scarlar coupling (through bonds), dipolar copuling (through space), chemical exchange.
Probe
Release the antenna
Responsible for sending in the radio frequency pulses for exitation, but also for picking up the signal
Console
Console:
Where everything is controlled.
The console wire the transmitter, that send in the pulses, nesessary to exite magnitization.
Magnet
Creates a strong magnetic field, enhances the population difference between the alfa and beta state.
The sample sit inside the magnet.
Adjusting the impedance of the probe to the desired level is called x.
The process of making the magnetic field homogeneous throughout the sample, is called: x
Adjusting the impedance of the probe to the desired level is called matching.
The process of making the magnetic field homogeneous throughout the sample, is called: shimming
The process where the frequency of the probe is adjusted to the desired resonance frequency, is called x.
The process where the frequency of the probe is adjusted to the desired resonance frequency, is called turning.
The radiofrequencypulses are sent by the x, and the signals are detected by the x.
The radiofrequencypulses are sent by the probe, and the signals are detected by the probe.
The console is the part of the spectrometer that creates the x and processes the signal from the sample.
The console is the part of the spectrometer that creates the radiofrequency waves and processes the signal from the sample.
Shim coils
creates inhomogenenous magnetic field with defines profiles which are used to cancel inhomogeneity present
how can Resolution be improved
improving field homogeneity, higher field strength, multiplication of FIDs.
what does every 2D-NMR consist of
PEMA
Preparation, Evolution, Mixing, Aquisition
Does T1-relaxation depend on the magnetic field strength?
Does T2-relaxation depend on solvent viscosity?
yes
yes
The type of nuclear magnetic relaxation that is responsible for the loss of phase coherence, is called x.
The type of relaxation, that causes the re-establishment of the equilibrium, is called x.
The type of nuclear magnetic relaxation that is responsible for the loss of phase coherence, is called transverse relaxation.
The type of relaxation, that causes the re-establishment of the equilibrium, is called longitudinal relaxation.
T1-relaxation is measured by the x experiment.
T2-relaxation is measured by the x experiment.
T1-relaxation is measured by the Inversion-Recovery experiment.
T2-relaxation is measured by the CPMG experiment.
Highest 1H-NMR shift: formaldehyde
second-highest 1H-NMR shift: benzene
third-highest 1H-NMR shift: ethene
fourth-highest 1H-NMR shift: acetylene
lowest 1H-NMR shift: ethane
The effect mainly responsible for the observed shift differences is called magnetic anisotropy. It is caused by π-electrons.
Highest 1H-NMR shift: formaldehyde
second-highest 1H-NMR shift: benzene
third-highest 1H-NMR shift: ethene
fourth-highest 1H-NMR shift: acetylene
lowest 1H-NMR shift: ethane
The effect mainly responsible for the observed shift differences is called magnetic anisotropy. It is caused by π-electrons.
NMR eksperimenter kan beskrives som
NMR eksperimenter kan beskrives som sekvenser af pulser, delays, og recordings.
