Integrative Graduate
Education and
Research Traineeship

Highlight

Distortion/Interaction Model of Organic Reactivity

Transition states of coronene reacting with dihydrogen (left) and ethylene (right). Distances are shown in Ångstroms.

Projects:

UCLA IGERT - Materials Creation Training Program (MCTP 2)

Institution:

University of California at Los Angeles

Primary Strategic Goal:

Learning: Build the Nation's research capability through critical investments in advanced instrumentation, facilities, cyber infrastructure, and experimental tools.

Secondary Strategic Goal:

Research Infrastructure: Build the Nation's research capability through critical investments in advanced instrumentation, facilities, cyber infrastructure, and experimental tools.

Achievement/Results

Theoretical work done by Amy Hayden in the Houk group has both contributed to the overall understanding of chemical reactivity as well as examined the behavior of polycyclic aromatic hydrocarbons (PAHs), molecules that have applications as organic semiconductors, in the presence of several common gaseous molecules. The reaction energetics of forty-three 1,4-dihydrogenation reactions of PAHs and nitrogen-containing heterocycles as well as the forty-three analogous Diels-Alder reactions with ethylene (C2H4) have been computed using B3LYP/6-31G(d) density functional theory. These groups of molecules were used as a test set to examine the applicability of the distortion/interaction model to reactions of these types. Distortion energy is the energy required to distort the reactants from their initial geometries to the transition state geometry, while interaction energy is the favorable electrostatic interaction experienced between these reacting fragments. This model, which was first established for 1,3-dipolar cycloadditions, proposes that the distortion energy is related to the activation energy. The computed transition state distortion energies of the reactions studied in this research correlate with the activation energies of these reactions, even for cases when the energy of reaction does not correlate with activation energy. From the results, it was concluded that the distortion/interaction model provides a better explanation than other known models of relative reactivities for these types of reactions. Typical transition states are shown in the Figure.

Reference

Hayden, A.E. & Houk, K.N. Transition State Distortion Energies Correlate with Activation Energies of 1,4-Dihydrogentations and Diels-Alder Cycloadditions of Aromatic Molecules. Journal of the American Chemical Society 2009, 131, 4084-4089.

Address Goals

The modifications of materials and surfaces (buckytubes and graphene, for example) through hydrogenations and cycloadditions are an important way to modify properties and extend applications.