Summary
Summary Nuclear magnetic resonance (NMR)
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Drug design and mechanisms of drug action - 1st semester Includes bullet points, key diagrams and images
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NMRNMR Theory
Nuclei have the property of spin
Spin quantum number (I)
I=1/2 as a proton
Nuclei have a positive charge so generate a magnetic field
Magnetic spin quantum number is direction of spin
m=2I+1
Magnetic field Bo provides the energy difference
Energy difference is small and allows spin flip
NMR measures the relaxation from excited state to ground state
Use 9.4T (400MHz) or biological 21.1T (900MHz)
Spectrum
Frequency (resonance) observed is dependant on the proton environment
Nucleus is affected by Bo but electrons also have a magnetic field which modifies
this
, Reference Compounds
TMS- tetramethylsilane
Chemical shift δ=0
It’s protons are very high field as they are very shielded
Can calculate δ using TMS
δ= v-v0/v0 where v0=reference resonance and v=observed resonance
Independent of magnetic strength
NMR Solvents
CDCL3 δ=7.2
DMSO δ=2.5 and around 3 there’s a water peak as hygroscopic
Interpreting NMR Spectra
Peak Positions (Chemical Shift δ)
Generally number of environments= number of different peaks
δ depends on degree of branching as you get electronic effects of neighbouring
atoms
δ CH>CH2>CH3
CH3 is most up field- EWG reduce shielding and resonance so moves it down field
More electronegative atoms increases resonance as electron density decreases
(shielding)
Can extend down an alkyl chain
Hydroxyl Groups
δ depends on the solvent as more dilute means a smaller
chemical shift as less hydrogen bonds
High concentrations decreases electron density, deshields
the group and gives a higher frequency
In carboxylic acids they can dimerise through hydrogen
bonding giving δ=10-12
CH2 In a Chain
Neighbouring carbon is electronegative so protons are deshielded and shifted
down field
δ=1.3-2.0ppm
CH In A Chain
δ=1.7-2.5ppm
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