Substituent Effects and Mechanism in a Mechanochemical Reaction.

Published

Journal Article

We report the effect of substituents on the force-induced reactivity of a spiropyran mechanophore. Using single molecule force spectroscopy, force-rate behavior was determined for a series of spiropyran derivatives substituted with H, Br, or NO2 para to the breaking spirocyclic C-O bond. The force required to achieve the rate constants of ∼10 s-1 necessary to observe transitions in the force spectroscopy experiments depends on the substituent, with the more electron withdrawing substituent requiring less force. Rate constants at 375 pN were determined for all three derivatives, and the force-coupled rate dependence on substituent identity is well explained by a Hammett linear free energy relationship with a value of ρ = 2.9, consistent with a highly polar transition state with heterolytic, dissociative character. The methodology paves the way for further application of linear free energy relationships and physical organic methodologies to mechanochemical reactions, and the characterization of new force probes should enable additional, quantitative studies of force-coupled molecular behavior in polymeric materials.

Full Text

Duke Authors

Cited Authors

  • Barbee, MH; Kouznetsova, T; Barrett, SL; Gossweiler, GR; Lin, Y; Rastogi, SK; Brittain, WJ; Craig, SL

Published Date

  • October 2, 2018

Published In

Volume / Issue

  • 140 / 40

Start / End Page

  • 12746 - 12750

PubMed ID

  • 30260221

Pubmed Central ID

  • 30260221

Electronic International Standard Serial Number (EISSN)

  • 1520-5126

International Standard Serial Number (ISSN)

  • 0002-7863

Digital Object Identifier (DOI)

  • 10.1021/jacs.8b09263

Language

  • eng