Pentalenene formation mechanisms reduxElectronic supplementary information (ESI) available: Coordinates and energies for all structures, and additional calculations mentioned in the text. See DOI: 10.1039/C3OB42005A

Quantum chemical calculations are used to assess various means of lowering the barrier for the dyotropic rearrangement previously proposed to occur during the carbocation rearrangement process promoted by pentalenene synthase. Several means of lowering this barrier, including a stepwise pathway for dyotropic rearrangement, are uncovered. The viability of various mechanisms for formation of the sesquiterpene pentalenene is assessed using quantum chemical calculations.