A new study shows that it is possible to use mechanical force to deliberately alter chemical reactions and increase chemical selectivity — a grand challenge of the field.

The study led by University of Illinois Urbana-Champaign researcher Jeffrey Moore and Stanford University chemist Todd Martinezz demonstrates how external mechanical forces alter atomic motions to manipulate reaction outcomes. The study findings are published in the journal Science.

«We think of chemical reactions as molecules moving on a surface of potential energy in the way hikers follow the contour map of mountains and valleys along a trail,» said lead author Yun Liu, a post-doctoral researcher in Moore’s research group. «A mountain along a reaction path is a barrier that needs to be traversed before the molecules can descend into their final product. Therefore, the relative height of barriers control which path the molecules will most likely choose, allowing chemists to make predictions about what a particular chemical reaction will produce — an outcome called selectivity.»

Chemists have traditionally assumed that the jiggling of molecules — known as «molecular dynamics» — is governed by a potential energy surface. Molecules transform by chemical reactions that seek the path requiring a minimum amount of energy. However, emerging evidence shows that molecules often do not have time to sample the surface, leading to deviations called nonstatistical dynamic effects, the researchers said.

Nonstatistical dynamic effects are observed in some common reactions such as nitration of benzene and dehydration reactions,» Liu said. «Despite these examples, NDEs have not fully captured chemists’ attention because they are difficult to measure and cannot be controlled to change the reaction outcomes — the essential pursuit of chemistry.»

Liu developed an experimental design using a carbon-13 isotope-labeled ring molecule with two polymer chains attached. Liu placed the polymers into a reaction vessel and applied a mechanical force via sonication, which rips the ring into two separate groups.

Story Source: Materials provided by University of Illinois at Urbana-Champaign, News Bureau. Original written by Lois Yoksoulian. Note: Content may be edited for style and length.