The selected electronic parameters of the studied molecules are numerically given in Table and graphically shown in Figure As a result, the difference between EVEA and EVIP, i.e. the chemical hardness η which is generally considered to be negatively correlated with the hyperpolarizability of the system, decreases first and then increases, and reaches a minimum at n = 3 of the (BN)nC(18-2n) (n = 1-9). Meanwhile, the η value of (BN)4C10 is only slightly higher than that of (BN)3C12. Moreover, compared with that of C18 ring, the parameters for measuring molecular reactivity, i.e. the chemical potentials |μ|, of (BN)nC(18-2n) (n = 1-9) decrease sequentially, which means that these hybrid rings are less reactive than C18, and their chemical inertness gradually increases with the number of B-N units in the molecule. It therefore can be inferred that when C-C pairs in the cyclocarbon are replaced by B-N units, the intermolecular covalent-coupling reactivity like that of pristine C18 will weaken, and the B-N analogues of cyclocarbons with large n value will have considerable chemical stability, making them an interesting synthetic target.