Rate constants and product distributions have been measured for the reactions of O(+)˙((4)S) with the methyl halides (CH(3)F, CH(3)Cl, CH(3)Br, CH(3)I) and three perfluorinated compounds (CF(4), SF(6), SF(5)CF(3)) at 300 K in a flowing afterglow-selected ion flow tube (FA-SIFT). The reactions occur with high efficiency, despite the necessity for spin conversion in some processes. The mechanisms include charge transfer, atom abstraction, and fragmentation reactions. Computational modeling was carried out to provide insight into these processes.
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.
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