On the basis of calculations using density functional theory, we show that C58N12, just as C48N12, can be a stable N-dopant of C-70. By considering many different isomers of the product, we find that the chemical stability of C48N12 and C58N12, with respect to oxygenation, is not significantly different from that of C70, thereby indicating that the N-dopant would not easily be oxygenated in air under normal conditions. In both C48N12O and C58N12O, many different isomers are expected, in which oxygenation occurs at different C-N bonds as well as at C-C bonds, among which specific C-N bonds are the most amenable to the reaction. Investigation of their hydrogenations shows that C48N12 is slightly more easily hydrogenated than C-60, while C58N12 is less easily hydrogenated. In addition, we expect a regiospecificity in the hydrogenated products of C58N12, which prefers to react at equatorial sites, while C-70 prefers reaction at polar sites. Meanwhile, comparison of the encapsulation energy of a nitrogen atom (-N-en) in C-60, C48N12, C-70, and C58N12 shows that the N-doped fullerenes, particularly C58N12, can encase the atom much better than the undoped ones, allowing us to expect the existence of N@C48N12 and N@C58N12. Spin multiplicities are doublet for most of their stable structures. These observations correlate with the formation of Nen-C bonds, which are not found in N@C-60 and N@C-70. Various isomers of the N-encapsulating fullerenes were identified. The relative stability of these isomers heavily depends on the number of substitutional nitrogen atoms around N-en-C bonds.