Mechanochemistry is an emerging field that studies reactions driven by a mechanical force. In polymer mechanochemistry, mechanical forces are harnessed by molecules known as mechanophores, which activate in response to an applied mechanical force. The application of mechanical force creates deformations on the potential energy surface (PES) of a mechanochemical reaction, thus potentially creating reaction pathways and products alternate to those observed via other means of activation. Flex-activated mechanophores are a subset of mechanophores which translate force into angular distortions that result in bond elongation; these distortions allow for the release small molecule products. Oxanorbornadiene is a flex-activated mechanophore that releases a furan when activated. Preliminary research has demonstrated that the introduction of a methyl group at carbon 1 of the oxanorbornadiene mechanophore’s bridgehead inhibits its mechanochemical activation. However, the role of steric and/or electronic encumbrance on the activation of oxanorbornadiene is not yet understood. The aim of this study is to control mechanophore activation by modifying the electronics and/or sterics at either side of the bridgehead. An additional goal is to explore if and how the PES deformations make the reaction pathway inaccessible. The force-modified reaction paths of a series of oxanorbornadiene mechanophores were determined computationally using Growing String Method, and the effects of the steric and electronic parameters were analyzed.

Elucidating steric and electronic impacts of functional groups on the potential energy surfaces of a series of oxanorbornadiene mechanophores using growing string method

ACS Fall 2021

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