The Gaussian 09, Revison E.01 and Gaussian 16, Revision A.03 suites were used for all calculations. Geometry optimizations and subsequent vibrational analyses were performed at either wB97XD/6-311++G** or wB97XD/cc-pVQZ. The wB97XD functional was used to account for long-range and dispersion interactions. Polarization functions were applied to account for effects from ring strain. Minima and were confirmed by means of vibrational analysis using the same functional/basis set combination: no imaginary frequencies were found. Natural bond orbital (NBO) second-order perturbation analyses and determination of Wiberg bond index (WBI) were performed at wB97XD/cc-pVQZ on coordinates optimized using the same functional/basis set combination. Pictures of molecular orbitals were rendered using the IQmol program. Table . - -