title: Measurement of a linear free energy relationship one molecule at a time.
abstract: A systematic study of the dehydrogenation of substituted thiophenols by controlled charge injection from the tip of a scanning tunneling microscope (STM) reveals a pronounced dependence of the reaction yield on the position and the chemical nature of the substituent. We evaluate the dehydrogenation rate of para-halo-substituted species within a linear free energy relationship, namely the Hammett equation. The resultant rho value of 1.4 can faithfully predict the reaction rates of molecules that are meta-halo-substituted or para-methyl-substituted. The positive sign of rho suggests a negatively charged transition state at the core of the STM-induced process, and the magnitude of the rho value indicates that the presence of the substrate does not preclude substantial substituent effects. The applicability of the Hammett equation to single-molecule chemistry offers facile prediction of the rate of STM-based single-molecule chemistry in a field, which so far has been addressed by focusing on involved quantum-mechanical modeling of its underlying processes.
authors.affiliation: Department of Chemistry, University of California, Riverside, CA 92521, USA.
authors.forename: B V
authors.initials: BV
authors.lastname: Rao
authors.forename: K-Y
authors.initials: KY
authors.lastname: Kwon
authors.forename: A
authors.initials: A
authors.lastname: Liu
authors.forename: L
authors.initials: L
authors.lastname: Bartels
mesh_terms: D019817:Benzoic Acid / Q000737:chemistry; D001703:Biophysics / Q000379:methods*; D003300:Copper / Q000737:chemistry; D006859:Hydrogen / Q000737:chemistry; D007700:Kinetics; D016252:Microscopy, Scanning Tunneling / Q000379:methods*; D008956:Models, Chemical; D010636:Phenols / Q000737:chemistry; D013438:Sulfhydryl Compounds / Q000737:chemistry; D013816:Thermodynamics; D013997:Time Factors; D014867:Water / Q000737:chemistry
chemical_list: D010636:Phenols; D013438:Sulfhydryl Compounds; D014867:Water; D003300:Copper; C042983:thiophenol; D006859:Hydrogen; D019817:Benzoic Acid