A Remote Stereochemical Lever Arm Effect in Polymer Mechanochemistry

Molecular mechanisms by which to increase the activity of a mechanophore might provide access to new chemical reactions and enhanced stress-responsive behavior in mechanochemically active polymeric materials. Here, single-molecule force spectroscopy reveals that the force-induced acceleration of the electrocyclic ring opening of gem-dichlorocyclopropanes (gDCC) is sensitive to the stereochemistry of an alpha-alkene substituent on the gDCC. On the similar to 0.1 s time scale of the experiment, the force required to open the E-alkene-substituted gDCC was found to be 0.4 nN lower than that required in the corresponding Z-alkene isomer, despite the effectively identical force-free reactivities of the two isomers and the distance between the stereochemical permutation and the scissile bond of the mechanophore. Fitting the experimental data with a cusp model provides force-free activation lengths of 1.67 +/- 0.05 and 1.20 +/- 0.05 angstrom for the E and Z isomers, respectively, as compared to 1.65 and 1.24 angstrom derived from computational modeling.