,
, -Modern Analytical Techniques 2
Nuclear Magnetic Resonance (NMR)
·
Nucleiofcertain atoms are considered to spin
· Protons and Neutrons Spin in opposite directions
· Nucleus Spins pair up
· When a nucleus has an odd pair of nucleons, there is a nucleon
with an unpaired spin
· This generates a magnetic field
· ifthe nucleus is placed in an external magnetic field can
it
↳line up with the external magnetic field
* line up against the external magnetic field
·
Alignmentwith external magnetic field is more stable. Energy mustbe
absorbed to flip nuclear magnetic field
· A
nucleus lined up againstthe field is regarded as less stable higher
energy state
o to flip the nucleus energy mustbe supplied equal to be
· When itflips from low to high, this is called exitation
· it will shortly flip back -
relaxation
o Process ofFlipping is called resonance
Magnetic field feltby a nucleus depends on
· Applied magnetic force
o weaker magnetic force generated electrons
by surrounding the nucleus
In nearby atoms -
nuclear shielding
· Extentofnuclear shielding depends on electron density in nearby atoms
groups ofatoms
o
changing environmentofthe nucleus
changes the energy gap
·
Spectrum shows many absorbtion peaks
· Relative positions reflectenvironments of nuclei
Two Types of NMR
· Proton NMR
· Carbon NMR
Data interpretation
· Number ofSignals -
no of environments
·
Position ofsignal-chemical shift-type ofenvironment
·
Intensity ofSignal- no. environment
ofnucleiin that
·
Splitting -
tells aboutenvironmentofa proton with to
respect other
nearby proton/Proton NMR only
, -Modern Analytical Techniques 2
Nuclear Magnetic Resonance (NMR)
·
Nucleiofcertain atoms are considered to spin
· Protons and Neutrons Spin in opposite directions
· Nucleus Spins pair up
· When a nucleus has an odd pair of nucleons, there is a nucleon
with an unpaired spin
· This generates a magnetic field
· ifthe nucleus is placed in an external magnetic field can
it
↳line up with the external magnetic field
* line up against the external magnetic field
·
Alignmentwith external magnetic field is more stable. Energy mustbe
absorbed to flip nuclear magnetic field
· A
nucleus lined up againstthe field is regarded as less stable higher
energy state
o to flip the nucleus energy mustbe supplied equal to be
· When itflips from low to high, this is called exitation
· it will shortly flip back -
relaxation
o Process ofFlipping is called resonance
Magnetic field feltby a nucleus depends on
· Applied magnetic force
o weaker magnetic force generated electrons
by surrounding the nucleus
In nearby atoms -
nuclear shielding
· Extentofnuclear shielding depends on electron density in nearby atoms
groups ofatoms
o
changing environmentofthe nucleus
changes the energy gap
·
Spectrum shows many absorbtion peaks
· Relative positions reflectenvironments of nuclei
Two Types of NMR
· Proton NMR
· Carbon NMR
Data interpretation
· Number ofSignals -
no of environments
·
Position ofsignal-chemical shift-type ofenvironment
·
Intensity ofSignal- no. environment
ofnucleiin that
·
Splitting -
tells aboutenvironmentofa proton with to
respect other
nearby proton/Proton NMR only
