Due to their unique physical properties, carbon nanotubes are a novel nanoscale environment in which to carry out chemical reactions. Reaction energetics, mechanism and dynamics could be significantly altered inside carbon nanotubes due to their large instrinsic polarizabilities and due to the severely decreased reaction volume. In an effort to examine the effect on reaction enthalpies and activation energies of confining reacting systems inside carbon nanotubes, calculations using hybrid density functional theory have been carried out for a model reaction.
In theoretical studies examining the effect of local environment of chemical reactivity, the Menshutkin SN2 reaction1 is often studied. In the present work, the effect of confinement of the Menshutkin SN2 reaction inside zigzag (8,0) and (9,0) carbon nanotubes is investigated. Compared to the gas phase, the potential energy surface changes dramatically. First, the ion pair product is significantly stabilized, making the overall process more favourable. Second, the transition state shifts towards the reactants and is stabilized, giving a lower reaction barrier, in agreement with the Hammond postulate. Comparison of the all electron nanotube calculations with a polarizable continuum model shows excellent agreement, confirming the stabilizing mechanism and suggesting a cost-effective method for investigating other confined chemistries.
The results presented here indicate that the effect of nanotube confinement on relative reaction energies closely resembles solvation and that chemical reactions in which there is a separation of charge along the reaction coordinate will be inhanced inside fullerene based materials due to their large electronic polarizabilities.
1 Menshutkin, N. Z. Phys. Chem.1890, 5, 589; Menshutkin N. Z. Phys. Chem.1890, 6, 41.
Mathew D. Halls
Scientific Simulation and Modeling Group, Zyvex Corporation,
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