The "facilitated transition" hypothesis as an explanation for the gemdialkyl effect
A new technique of searching the conformational space of transition states was used to explore the cause of the rate acceleration in the gem-dialkyl effect in intramolecular cyclization reactions. Several previous hypotheses were discarded and a new hypothesis was advanced based on this new data. This hypothesis, the "Facilitated Transition" hypothesis, states that increased steric hindrance reduces the overall activation energy by facilitating rotation through the transition state. The older "Reactive Rotamer" hypothesis was eliminated by generating all conformations of the starting materials using the WIZARD and MM2 computer programs and demonstrating that no relationship is found between rate increase and a change in the concentration of "reactive rotamers".
Journal of Molecular Structure: THEOCHEM
Parrill, A., & Dolata, D. (1996). The "facilitated transition" hypothesis as an explanation for the gemdialkyl effect. Journal of Molecular Structure: THEOCHEM, 370 (2-3), 187-202. https://doi.org/10.1016/S0166-1280(96)04701-X