Gronert Scott, Garver John M, Nichols Charles M, Worker Benjamin B, Bierbaum Veronica M
Department of Chemistry, Virginia Commonwealth University , 1001 W. Main Street, Richmond, Virginia 23284-2006, United States.
J Org Chem. 2014 Nov 21;79(22):11020-8. doi: 10.1021/jo502039h. Epub 2014 Nov 7.
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.
在选择离子流动管（SIFT）中研究了以碳和氮为中心的亲核试剂与多氟溴苯的气相反应，并在MP2/6-31+G(d,p)//MP2/6-31+G(d)水平上进行了计算建模。在气相实验中，测定了速率常数和分支比。碳亲核试剂产生预期的亲核芳香取代（SNAr）和质子转移产物，以及由溴中心（多氟苯负离子离去基团）的SN2反应产生的意外产物。对于氮亲核试剂，溴处的SN2通道受到抑制。在SNAr通道中，观察到“元素效应”，氟化物损失与溴化物损失相互竞争。计算建模表明，所有取代势垒都远低于入口通道，熵和动力学效应控制着产物分布。
