title: Dehalogenation of arenes via SN2 reactions at bromine: competition with nucleophilic aromatic substitution.
abstract: The gas-phase reactions of carbon- and nitrogen-centered nucleophiles with polyfluorobromobenzenes were examined in a selected-ion flow tube (SIFT) and modeled computationally at the MP2/6-31+G(d,p)//MP2/6-31+G(d) level. In the gas-phase experiments, rate constants and branching ratios were determined. The carbon nucleophiles produce expected nucleophilic aromatic substitution (SNAr) and proton transfer products along with unexpected products that result from SN2 reactions at the bromine center (polyfluorophenide leaving group). With nitrogen nucleophiles, the SN2 at bromine channel is suppressed. In the SNAr channels, the "element effect" is observed, and fluoride loss competes with bromide loss. The computational modeling indicates that all the substitution barriers are well below the entrance channel and that entropy and dynamics effects control the product distributions.
authors.affiliation: Department of Chemistry, Virginia Commonwealth University , 1001 W. Main Street, Richmond, Virginia 23284-2006, United States.
authors.forename: Scott
authors.initials: S
authors.lastname: Gronert
authors.forename: John M
authors.initials: JM
authors.lastname: Garver
authors.forename: Charles M
authors.initials: CM
authors.lastname: Nichols
authors.forename: Benjamin B
authors.initials: BB
authors.lastname: Worker
authors.forename: Veronica M
authors.initials: VM
authors.lastname: Bierbaum
mesh_terms: D001966:Bromine / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D003198:Computer Simulation; D054879:Halogenation; D006846:Hydrocarbons, Halogenated / Q000737:chemistry*; D007477:Ions / Q000737:chemistry*; D008956:Models, Chemical; D009584:Nitrogen / Q000737:chemistry*; D055601:Organic Chemistry Phenomena
chemical_list: D006846:Hydrocarbons, Halogenated; D007477:Ions; D002244:Carbon; D009584:Nitrogen; D001966:Bromine