Organic Chemistry: NMR Spectroscopy concept question

[ephemeral1]

Why are sp2 carbons more downfield than sp3 carbons? Is it because the bond length of sp2 carbons is shorter (electrons are more localized-thus more shielded)?

 

[chemisttree]

It has to do with the double bond. Look up "diamagnetic anisotropy". There is a 'ring current' that is set up in a double bond that produces zones of shielding and deshielding. The position of the proton in either one of these two zones determines the direction and magnitude of the apparently anomalous shift.