C-78 is one of the most widely investigated higher fullerenes. Among its huge isomer family, only one non-IPR (IPR = isolated pentagon ring) cage, the C-2-symmetric C-#22010(78), was previously stabilized by endohedral derivatization. Here we report a new C-1-symmetric non-IPR hollow isomer, C-#23863(78), which was captured as (C78Cl8)-C-#23863 and then subjected to a regioselective substitution reaction with benzyl hydroperoxide to form C-#23863(78)(OOCH2C6H5)Cl-7. The structural connectivity of C-#23863(78), which contains a pair of fused pentagons, was confirmed by single-crystal X-ray diffraction analysis of the C-#23863(78)(OOCH2C6H5)Cl-7 molecule, which shares the same fullerene core with (C78Cl8)-C-#23863, support for the structure is provided by comparable IR measurements and computation. Theoretical studies suggest that the differences in C-Cl bond length, intermediate stability, and steric effects of the involved molecules account for the chemical regioselectivity of the substitution reaction.