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 <i>gem</i>-dichloro­cyclo­propanes (<i>g</i>DCC) is sensitive to the stereo­chemistry of an α-alkene substituent on the <i>g</i>DCC. On the ∼0.1 s time scale of the experiment, the force required to open the <i>E</i>-alkene-substituted <i>g</i>DCC was found to be 0.4 nN lower than that required in the corresponding <i>Z</i>-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 Å for the <i>E</i> and <i>Z</i> isomers, respectively, as compared to 1.65 and 1.24 Å derived from computational modeling