Induction , resonance , and hybridization modulate electron density at the proton, as the result of local electron currents around the nucleus;. precession of electrons attached to substituent.
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Induction, resonance, and hybridization modulate electron density at the proton, as the result of local electron currents around the nucleus;
precession of electrons attached to substituent
Purely magnetic effects of substituents also can have major effects on proton shielding if the group has a non-spherical shape generating a non-local field;
Non-spherical electron density distributions generatediamagnetic anisotropy
change of sign at an angle of 54º44from the plane of the ring;
it is the zero value of the expression3cos2q-1, the magic angle in NMR;
The larger non-local shielding effect is seen when the C-C bond is perpendicular to B0;
for methylene of the type Y-CH2-X by adding Di to the chemical shift of methane;
d = 0.23 + DX + DY
d = 5.28 + Zgem + Zcis+ Ztrans
d = 7.27 + ∑Si