The isosurface and color-filled map of the ZZ component of ICSS, referred to as ICSS ZZ , for the three precursors C 18 -(CO) n (n = 6, 4, and 2) are shown in Fig. . It can be seen that there is a shielding area inside the ring protruding in the direction perpendicular to the ring plane, surrounding by a toroidal deshielding area outside the ring. The shielding/deshielding characteristics of C 18 -(CO) n (n = 6, 4, and 2) once again indicate that they should be considered as a system with remarkable aromaticity, since typical aromatic systems share the same feature of ICSS ZZ . From the figure it is obvious that the peripheral deshielding region of each molecule is interrupted by the -CO groups, and the more -CO groups there are, the more severe the interruption is. The reason for this is clearly explained by the previous orbital interaction analysis, that is the existence of the -CO groups breaks the conjugation of  in electrons and hence the corresponding in-plane induced current. The strong interference of magnetic shielding characteristics is therefore generated. Note that from color-filled map in Fig. , the color inside/outside the ring become redder/bluer with decrease of the number of -CO groups, displaying stronger shielding/deshielding effect. This observation clearly demonstrates that from C 18 -(CO) 6 to C 18 -(CO) 4 then C 18 -(CO) 2 , the molecule becomes more and more aromatic. The ICSS ZZ values calculated at 1 Å above the center of the ring, referred to as ICSS ZZ , is quite robust and popular for quantitatively determining aromaticity of ring systems. The ICSS ZZ (1) values of C 18 -(CO) n (n = 6, 4, and 2) are observed to be 4.0, 7.8, and 15.3 ppm for n = 6, 4, and 2, respectively, which are lower than that of C 18 and benzene (29.9 ppm) , indicating that a relative weak but still distinct aromaticity in the molecules. The order of aromaticity strength determined by the ICSS ZZ (1) is also fully consistent with the judgment results from all above visual analyses.