Increment systems, diamagnetic anisotropies

The decreasing aromaticity in the anion is also manifested in a smaller magnetic sus-ceptibihty exaltation (A) , which is defined as the difference between the bulk magnetic susceptibility (xm) of a compound and the susceptibility (xm ) estimated from an increment system for the same structure without cyclic conjugation (A = xm — Xm in units of ppm cgs). Thus, the value A = —9.1 for PhO is equal to only 59% of the A = —15.5 for phenol. The computed values for the diamagnetic susceptibility anisotropy (Xanis) follow the same trend, indicating that PhO has actually about 60% of the aromaticity of PhOH352. 

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