Minimals: NMR ESR Flashcards
List at least three nuclei which can be used in NMR
1H 2H 13C 14N 19F 31P
Which nuclei are able to given an NMR signal?
Whose resultant nuclei spin is not zero. Those nuclei which contain odd number of protons and/or odd number of neutrons.
What happens to the elementary magnetic moments in an external magnetic field?
The interaction of magnetic moments with the external magnetic field caused their alignment as well as their precession about the magnetic field.
What are the possible states of the magnetic moment of a 1H nucleus in an external magnetic field?
The nuclei spin of 1H is 1/2, therefore it’s magnetic moment has two possible alignments with respect to the magnetic field:
It can be either parallel with(lower energy) or anti parallel with(higher energy) the magnetic field.
Hat region of the electromagnetic spectrum can be used to excite nuclear and electron spins placed in a magnetic field?
Radio waves(~10 to the power of 8 Hz): NMR microwaves(~10 to the power of 10 Hz): ESR
What is the nuclear magneton?
It is a physical constant and the natural unit for expressing magnetic dipole moments of heavy particles. (Eg. Nucleons, atomic nuclei)
Why are the resonance frequencies applied in ESR much higher than those used in NMR in a given magnetic field?
The energy difference between the ground states and excited states is linear proportional to the Bohr(ESR) or the nuclear magneton(NMR). Since the mass of the proton is abt 2000 times greater than that of an electron, the Bohr magneton, the energy difference between the two states will be much higher in ESR
What factors influence the resonance frequency in NMR
Quality of the absorbing nucleus
Its chemical environment
Strength of the external magnetic field
How can the relative concentration of absorbing nuclei be determined from an NMR spectrum?
From the area under the absorption lines corresponding to different nuclei.
What is the chemical shift in NMR?
The local magnetic field experienced by a given nucleus is altered by the chemical environment resulting in a change in its original resonance frequency.
What is the equilibrium occupancy of the two states of 1H nuclei in a magnetic field?
The occupancies of the two states are determined by the Boltzmann distribution the lower energy level(parallel alignment) contains slightly more nuclei than the higher level(anti parallel alignment)
What is the macroscopic consequence of the alignment of nuclear magnetic moments by the external magnetic field?
A macroscopic magnetization (equilibrium or longitudinal magnetization) is formed in the direction of the external magnetic field
What provides the signal in pulse NMR techniques?
The precession of transverse magnetization generated by a short, intense radiofrequency pulse. Precession takes place at the resonance frequency of the nucleus in the given magnetic field.
What is spin-spin and spin-lattice relaxation?
Spin-spin relaxation is the mechanism responsible for the decay of transverse magnetization generated by RF pulse.
Spin-lattice relaxation is responsible for the recovery of the original longitudinal magnetization vector.
What kind of parameters does an MRI image reveal?
About the density of 1H nuclei in a volume unit(voxel) and about their spin-spin and spin-lattice relaxation rates.
