The electrostatic potential map placed around the molecule shows how the electron density varies around the different atoms in the molecule. There is a very high electron density around the oxygen atom, as would be expected of a very electronegative element. This high electron density affects the magnetic field felt by the neighboring carbon and hydrogen atoms, called shielding. The effect of shielding is to move the peak further downfield (to the left) than it would normally be. This is known as the chemical shift.