Density functional and ab initio methods have been used to study the mechanisms for key dynamic processes of the experimentally known S-4-symmetric [16] annulene (1a). Using BH& HLYP/6-311+ G** and B3LYP/6-311+G**, we located two viable stepwise pathways with computed energy barriers (E-a = 8-10 kcal/mol) for conformational automerization of 1a, in agreement with experimental data. The transition states connecting these conformational minima have Mobius topology and serve as starting points for non-degenerate pi-bond shifting (configuration change) via Mobius aromatic transition states. The key transition state, TS1-2, that connects the two isomers of [16]annulene (CTCTCTCT, 1 -> CTCTTCTT, 2) has an energy, relative to the S-4 isomer, that ranged from 6.9 kcal/mol (B3LYP/6-311+G**) to 16.7 kcal/mol (BH&HLYP/6-311+G**), bracketing the experimental barrier. At our best level of theory, CCSD(T)/cc-pVDZ(est), this barrier is 13.7 kcal/mol. Several other Mobius bond-shifting transition states, as well as Mobius topology conformational minima, were found with BH&HLYP energies within 22 kcal/mol of 1a, indicating that many possibilities exist for facile thermal configuration change in [16] annulene. This bond-shifting mechanism and the corresponding low barriers contrast sharply with those observed for cis/trans isomerization in acyclic polyenes, which occurs via singlet diradical transition states. All Mobius bond-shifting transition states located in [16]- and [12] annulene were found to have RHF -> UHF instabilities with the BH& HLYP method but not with B3LYP. This result appears to be an artifact of the BH&HLYP method. These findings support the idea that facile thermal configuration change in [4n] annulenes can be accounted for by mechanisms involving twist-coupled bond shifting.