MR spectroscopy
Nuclear Magnetic Resonance usedto help determine structure of a molecul
if atomic nucleus has odd numbe of nucleons protonsand neutrons then
has a nuclear spin creates a weak magnetic field NMRdetects how
nese magnetic fields are affected by a larger external magnetic field
2types 713C NMR info on how carbon atoms are arranged
H NMR info on how hydrogen atoms are arranged
Nuclei spin in random directions however when
n external magnetic field is applied they align in
directions either in the direction of the
xternal magnetic field or against it those that
in in direction of magneticfield have lower
nergy
NMRfires out radio waves at aspecificfrequency
vclei that arealignedwithmagnetic field absorbthe
nergy and flip to the higher level those with higherenergy can also drop to
wer energy and emit radio waves
initially there are more nucleialigned with magnetic field so overall more
nergy absorbed than emitted
is
NMR measures amount of energyabsorbed
magnetic field will be felt by the nucleidifferentlydependingon the environme
is in as they absorbdifferentamounts of energy and various frequencies NM
ectroscopy picksup this difference
atoms andgroupsof atoms adjacentto thenucleusaffect level of shielding
shields nucleus from external magnetic field
environment isdeterminedby thegroupsof atoms that exist nearnucleibeing
xamined look along full chain for atoms to be in the same environment the
Ustbebonded to an atom or group of atoms that are identical
identifying carbon and hydrogenenvironments
beg
TMS tetra methylsilane is used as a standard when looking atchemicalShi
difference between the TMS peak and peaksproduced by the substance
called the chemical shift s
chemical shift s measured in partsper million ppm because it isuse
s a standard we assign this peak 8 0
TMS used to calibrate NMRmachines when analysingsamples
TMS TMS has 12hydrogens all in identical environments
n c stitch will produce a large singlepeak well away from
this sample peaks
TMS is inert non toxic and volatile so easy to remove fromsample
C NMR
carbon closest to an electronegative atom electron shielding lower and
o chemical shift s is higher further to right on spectrum
cycliccompounds use line of symmetry to find carbon environments
match value ofchemicalshift to those in data book however cannot
etermine whether peak at 190 is for an aldehyde or a ketone and there
Nuclear Magnetic Resonance usedto help determine structure of a molecul
if atomic nucleus has odd numbe of nucleons protonsand neutrons then
has a nuclear spin creates a weak magnetic field NMRdetects how
nese magnetic fields are affected by a larger external magnetic field
2types 713C NMR info on how carbon atoms are arranged
H NMR info on how hydrogen atoms are arranged
Nuclei spin in random directions however when
n external magnetic field is applied they align in
directions either in the direction of the
xternal magnetic field or against it those that
in in direction of magneticfield have lower
nergy
NMRfires out radio waves at aspecificfrequency
vclei that arealignedwithmagnetic field absorbthe
nergy and flip to the higher level those with higherenergy can also drop to
wer energy and emit radio waves
initially there are more nucleialigned with magnetic field so overall more
nergy absorbed than emitted
is
NMR measures amount of energyabsorbed
magnetic field will be felt by the nucleidifferentlydependingon the environme
is in as they absorbdifferentamounts of energy and various frequencies NM
ectroscopy picksup this difference
atoms andgroupsof atoms adjacentto thenucleusaffect level of shielding
shields nucleus from external magnetic field
environment isdeterminedby thegroupsof atoms that exist nearnucleibeing
xamined look along full chain for atoms to be in the same environment the
Ustbebonded to an atom or group of atoms that are identical
identifying carbon and hydrogenenvironments
beg
TMS tetra methylsilane is used as a standard when looking atchemicalShi
difference between the TMS peak and peaksproduced by the substance
called the chemical shift s
chemical shift s measured in partsper million ppm because it isuse
s a standard we assign this peak 8 0
TMS used to calibrate NMRmachines when analysingsamples
TMS TMS has 12hydrogens all in identical environments
n c stitch will produce a large singlepeak well away from
this sample peaks
TMS is inert non toxic and volatile so easy to remove fromsample
C NMR
carbon closest to an electronegative atom electron shielding lower and
o chemical shift s is higher further to right on spectrum
cycliccompounds use line of symmetry to find carbon environments
match value ofchemicalshift to those in data book however cannot
etermine whether peak at 190 is for an aldehyde or a ketone and there
