EPR Flashcards
Types of EPR coordinates
Hyperfine: electron and nucleus
Electron Zeeman: electron and magnet
Nuclear Zeeman: nuclear and magnet
Equation for magnetic dipole
(-) g factor x bohr magnetion x spin
What is EPR spectroscopy
Unpaired electron, using the magnetic field of microwave radiation
Electron Zeeman Equation
g value x bohr magneton x magnetic field x spin
KEY: reference sample to determine g value
g ref x B ref / B sample
KEY: g value from data
planks x frequency / Bohr magneton x B
Nuclear Zeeman equation
g(N) x nuclear magneton x magnetic field x spin
Hyperfine interactions equation
Spin (e) x Hyperfine x spin (nuc)
How do you predict spectra using trees
Largest splitting closest to radical
Branches into next closest atoms (do both even if in same environment)
Ratio gives intensities
KEY: How do you predict spectra using equations
Nuclear spin = 1/2
Lines = 2 x number of equiv nuclei x spin + 1
Intensity is Pascal’s triangle
Nuclear spin = 1
Intensity is form of Pascal’s triangle
How to tell if doublet of triplets OR triplet of doublets
The one with the biggest splitting is the first word ie that environment is a doublet so it’s a doublet of triplets
Rules for interpreting spectra from STRUCTURE
Find number of different nuclear environments
Use 2nI+1 to predict
Rules for interpreting spectra from SPECTRA
Work from outside in
Measure separation between first two lines: Hyperfine
Look at intensity
Measure separation distance to next line
If same it’s the same multiplet if not they have overlapped
J value at centre of multiplet
How to find electronic structure
Find theoretical Hyperfine values
Find electron spin density
Find radical distribution
Draw orbital structure
Theoretical Hyperfine values
Constants calculated and dependent on nuclear and electronic wavefunction
Electron spin density equation: where electron is on nucleus
Experimental Hyperfine / theoretical Hyperfine
Equation for radical electron distribution
Molecule orbital = the sum of atomic orbital coefficient x atomic orbital
What is the spin density
The probability electron is localised on that atomic orbital
The sum of (atomic orbital coefficients)^2
When to use each Hyperfine constant
H closest to radical: McConnell coupling
H further away : hyperconjugation
Equation for McConnell coupling constant
a = - Q x spin density
Equation for hyperconjugation constant
a = B x spin density x cos^2(dihedral angle)
Geometry effects Hyperfine
What is a spin trap
Stabilises reactive intermediates so you can analyse them. Use common ones so you can remove them from your data effectively as the nature changes after with radical. Data from databases
Equation for spin trap binding
Radical (paramagnetic) + ST (diamagnetic) —> STR (paramagnetic)
Types of spectral linewidths
Homogeneous
Inhomogeneous
What is homogeneous broadening
Radicals experience magnetic field identically. Lorenzian line shames broad in wings
What is inhomogeneous broadening
Difference in magnetic field experienced by radicals. Gaussian lineshape: thinner
What is anisotropic EPR
Sensitive to orientation
Carried out at low temp
Solid or frozen sample
Variables to consider for anisotropic EPR
Temperature, pressure and light intensity.
Energy is proportional to direction of spin
g value and a value of anisotropic EPR
Total of values at x/y/z angles to magnetic field, divided by 3
