Investigation of pure inductive effects on benzene ring by 13C NMR chemical shifts: A theoretical study using fictitious nuclear charges of hydrogen atoms (‘H∗ method’)

Using fictitious hydrogen atoms (H∗) bearing a non-integer nuclear charge Z∗ enables us to study directly and continuously inductive effects at a given magnitude. We then investigate pure inductive effects on benzene carbon-13 chemical shifts, freely from real substituents. xhibit a linear dependence on the nuclear charge Z∗, with a well-known reverse effect for ortho position: this implies two opposite mechanisms, namely the ‘classic’ inductive effect and π-polarization. A comparison with 4-H∗-substituted bicyclo-[2.2.2]-octanes highlights the predominance of the latter one for the para-substitution. ditivity of inductive effects on chemical shifts is also directly proved by using poly-H∗-substituted benzenes.