Chemical Shift

Again, consider Maxwell’s theorem that an electric current in a loop generates a magnetic field.   Effectively, the electron distribution in the chemical will cause distinct local magnetic fields that will either add to or subtract from Bo

HO-CH2-CH3

Beff = Bo( 1 - s )

de-shielding                                      high shielding

Shielding – local field opposes Bo

Aromaticity, electronegativity and similar factors will contribute to chemical shift differences