Definition of NMR
Nuclei with magnetic properties occurs resonance transitions phenomenon between its magnetic energy in a static magnetic field and the electromagnetic wave, which is called nuclear magnetic resonance (NMR) phenomenon.
This post is aiming at introducing something before H NMR experiment.
NMR resonance condition
Nuclei with magnetic; external static magnetic field; the RF pulse with a certain frequency and its formula.
Concept and production of the chemical shift
According to the definition of NMR, the same type of nucleus referring to bare nuclei share the same resonance frequency. The chemical environment is not considered. In fact, when the nuclei are in different groups (different chemical environment), they have the different magnetic fields.
NMR conditions:
Because there is extranuclear electron cloud of different groups, this causes a certain shielding effect on nucleus.
Induced magnetic field generated by extranuclear electron cloud in external static magnetic field:
H’= -σH0 (σ:magnetic shielding constant)
The magnetic field felt by nuclear is generated by the applied magnetic field and the static magnetic field:
H= H0- H’= H0-σH0 =(1-σ)H0
Therefore, actual resonance frequency of the nucleus is:
For nuclei with the same element, if it is in the different groups (chemical environment), the electron density around the nucleus is different. Thus they have different resonant frequenciesυ, producing chemical shift.
Chemical shifts (δ) is defined as:
Operate mode of NMR
Continuous wave: Inverter operating frequency with a fixed magnetic field and Changing magnetic field sweep mode with fixed frequency.
Pulse wave: A pulse corresponds to issue all the frequencies within a very short time, so that all the nuclear resonance will happen in this frequency range simultaneously. Then detecting energy released in different chemical environments in which each nucleus returns from high-energy state to a lower energy state.
These are something that you must know before doing an experiment of NMR. In our next post, we will illustrate the detailed steps for this experiment.
Nuclei with magnetic properties occurs resonance transitions phenomenon between its magnetic energy in a static magnetic field and the electromagnetic wave, which is called nuclear magnetic resonance (NMR) phenomenon.
This post is aiming at introducing something before H NMR experiment.
NMR resonance condition
Nuclei with magnetic; external static magnetic field; the RF pulse with a certain frequency and its formula.
Concept and production of the chemical shift
According to the definition of NMR, the same type of nucleus referring to bare nuclei share the same resonance frequency. The chemical environment is not considered. In fact, when the nuclei are in different groups (different chemical environment), they have the different magnetic fields.
NMR conditions:
Because there is extranuclear electron cloud of different groups, this causes a certain shielding effect on nucleus.
Induced magnetic field generated by extranuclear electron cloud in external static magnetic field:
H’= -σH0 (σ:magnetic shielding constant)
The magnetic field felt by nuclear is generated by the applied magnetic field and the static magnetic field:
H= H0- H’= H0-σH0 =(1-σ)H0
Therefore, actual resonance frequency of the nucleus is:
For nuclei with the same element, if it is in the different groups (chemical environment), the electron density around the nucleus is different. Thus they have different resonant frequenciesυ, producing chemical shift.
Chemical shifts (δ) is defined as:
Operate mode of NMR
Continuous wave: Inverter operating frequency with a fixed magnetic field and Changing magnetic field sweep mode with fixed frequency.
Pulse wave: A pulse corresponds to issue all the frequencies within a very short time, so that all the nuclear resonance will happen in this frequency range simultaneously. Then detecting energy released in different chemical environments in which each nucleus returns from high-energy state to a lower energy state.
These are something that you must know before doing an experiment of NMR. In our next post, we will illustrate the detailed steps for this experiment.