Pi-Electron Charge Densities and Chemical Shifts in Nitrogen Heterocyclics

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Abstract
The relation Δσ = aΔq is examined in some detail, where Δσ is the chemical shift between a proton in an aromatic nitrogen heterocyclic and the corresponding proton in its aromatic polycyclic analog, and Δq is the excess π‐electron charge density on the carbon to which the proton is bonded in the heterocyclic. It is found that the relation is quite satisfactory for positions ortho to a nitrogen, as long as only one nitrogen appears in that particular cycle.