ABSTRACT

The purpose of this study is to utilize computational techniques in the determination of the mechanistic pathways for the one-pot conversion of a pentacyclo-undecane (PCU) dione 1 to a pentacyclo-undecane cage lactam 2.

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The mechanism proposed [1] for this unique conversion was based on chemical intuition. In pursuance the ab initio quantum mechanical level of theory was employed. The primary goal of this study was to compute the relative difference in energies for the reactants, products and transition states of the proposed mechanistic pathways. The energy values obtained were used to predict the thermodynamic and kinetic pathways of the mechanism. All calculations were performed using the GAUSSIAN 98 series of programs, and GAUSS VIEW was used to visualize the transition state structures.

Full geometry optimizations were performed at the Hartree-Fock (HF) level of theory using the 6-31+G* basis set. In addition, the transition states were established using a SCAN technique to obtain a starting structure. Transitions states were verified by using the second-derivative analytical vibrational frequency calculations and the visual inspection of the movement of atoms associated with the transition.

Hess’s Law was applied to compute the heats of formation. It was found that two transition structures in the gas phase had abnormally high energies. However, these energies were found to be considerably lower in the presence of a solvent molecule. Furthermore, it was observed the one-step conversion of the dione 1 to the lactam 2 proceeded via a single transition state.

Previous experimental work found that the reaction proceeds through a cyanohydrin intermediate which in all likelihood represents the rate determining step. Sound arguments exists [2] to demonstrate that the computationally determined rate-determining step agrees with the experimentally observed rate-determining step.