The cause for this is due to the movement of the electrons in the pi bond of the carbon-carbon double bond and how the magnetic field effects the protons bound to the pi bond. The circular motion actu...The cause for this is due to the movement of the electrons in the pi bond of the carbon-carbon double bond and how the magnetic field effects the protons bound to the pi bond. The circular motion actually reinforces the external field at the edge of the double bond on both sides of the pi bond but creates a local field (shown in purple and green) that opposes the external field in the center of the double bond.
