We use a combination of the quantum chemical force field for pi electrons (QCFF/PI) method and the modified neglect of differential overlap-parametrization method 3 (MNDO-PM3) to predict some properties of the nine isomers of C-82 that satisfy the isolated pentagon rule. All the structural parameters are optimized with both methods. The two calculations furnish a coherent picture for the relative stabilities, energy ordering, and energy differences among the nine clusters. A C-2 isomer is the most stable while the two C-3 upsilon isomers are the least stable. The two methods also agree in the energy trends of the HOMOs and LUMOs. The nine C-82 molecules have HOMOs at higher energies and LUMOs at lower energies than C-60 and C-70. On a qualitative basis, they are therefore better electron donors and better electron accepters. The HOMO-LUMO energy gap is smaller for the less stable species, with the energy of the LUMO more strongly affected upon changing the isomer. In an effort to contribute to the identification of the different isomers, we predict the infrared spectra of all nine molecules by a combination of the QCFF/PI force fields and MNDO-PM3 derivatives of the dipole moments. The QCFF/PI vibrational frequencies are scaled By analogy with the analysis of the neutron scattering spectrum of C-70 The normal modes are overlapped to the MNDO-PM3 derivatives of the dipole moments to yield the infrared intensities. The infrared fingerprints of the nine molecules are reasonably different both in patterns and in intensities, with the more stable isomers having less intense infrared spectra. This behavior is rationalized by a simple physical model.