NMR + EPR

nucleus sees greater field than expected nucleus = more exposed to magnetic field EWG cause deshielding signal moves downfield (more +ve)

electrons in ground state produces a field that opposes B0 + sees smaller field more e- around nucleus => less exposed to magnetic field EDG cause shielding signal moves upfield (more -ve)

shielding increases as electronegativity decreases

more ED = better back donation into CO ligand = increase in chemical shift pushes e- density into metal/anti-bonding orbital (offload via back bonding) => deshields C nucleus

upfield shift as coordination number increases larger no. of ligands = more shielded nucleus

upfield shift as oxn state decreases more e- rich metal = more shielded nucleus

decreased shielding relative to atomic size larger atom -> start filling f orbitals = more shielding

proton decoupled only observe P

increases as s-character of bond increases

increasing coordination number decreases coupling constant more bonds means hybridisation of central atom changes (s-character decreases as no. of ligands increases)

sp > sp2 > sp3 more s-character = bigger coupling constant

higher electronegativity = bigger coupling constant

π acidic ligands reduce coupling constant groups that are trans to one another = larger coupling constant

polarisation

as oxn state increases, polarisation = more difficult higher oxn state = smaller coupling constant

coupling constant decreases when l.p. are coordinated

increasing bond angle = increasing s-character = larger J value

how good a nucleus is at NMR sensitivity (S/N ratio) may be estimated in terms of receptivity large gyromagnetic ratio + natural abundance = large receptivity

occurs when active nucleus is not 100% abundant central peak = inactive isotope (e.g. 12C) -> no coupling satellites = active isotope (e.g. 13C)

e.g. PF5 [rtp] -fluxional behaviour = v. rapid -all F = equivalent = BROAD SINGLET [low temp.] -freeze fluxional behaviour of Berry pseudorotation -equatorial + axial not equal = TRIPLET OF QUARTETS

axial

paired vs unpaired electrons nuclear vs electron spin chemical shift vs g-value (field(B), Gauss or mT) J value (coupling constant, Hz) vs hyperfine coupling (Gauss)

value = important (helps identify radical) size of g-value influenced by spin-orbital coupling (i.e. what else is near radical) organic radicals = small g-value main group + transition metal radicals = large g value

ge = 2.0023 ge = free-electron g factor = dimensionless factor that corrects magnetic moment of quantum electron from classical result