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Unformatted text preview: magnetic field, B o , the electrons circulate around the nucleus resulting in an induced magnetic field, b , with lines of force opposing B o at the nucleus. B o b Influence of Shielding on the Chemical Shift B o A resonance of H with no electrons B "upfield" shift in resonance due to b C in presence of an electronegative group The extent of the "upfield" shift due to shielding depends on the electron density around the H. If there is a nearby electronegative group that decreases the electron density, the resonance will shift "downfield." The induced magnetic field requires the applied (external) magnetic field to be stronger than what is needed to achieve resonance in a proton where there are no circulating electrons....
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