title: A remote stereochemical lever arm effect in polymer mechanochemistry.
abstract: 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 α-alkene substituent on the gDCC. On the ∼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 Å for the E and Z isomers, respectively, as compared to 1.65 and 1.24 Å derived from computational modeling.
authors.affiliation: Department of Chemistry, Duke University , Durham, North Carolina 27708, United States.
authors.forename: Junpeng
authors.initials: J
authors.lastname: Wang
authors.forename: Tatiana B
authors.initials: TB
authors.lastname: Kouznetsova
authors.forename: Zachary S
authors.initials: ZS
authors.lastname: Kean
authors.forename: Lin
authors.initials: L
authors.lastname: Fan
authors.forename: Brendan D
authors.initials: BD
authors.lastname: Mar
authors.forename: Todd J
authors.initials: TJ
authors.lastname: Martínez
authors.forename: Stephen L
authors.initials: SL
authors.lastname: Craig