Chemistry of Nuclear Recoil 18F Atoms. V. Mechanism and Systematics in CH3CF3

Nuclear recoil ¹⁸F atoms undergo hot F‐for‐F and F‐for‐H atomic substitution and hot F‐for‐CH₃ and F‐for‐CF₃ alkyl replacement reactions in CH₃CF₃. The primary absolute yields corresponding to these processes are $\text{3.56 ± 0.07,\hspace{0.17em}8.22 ± 0.09,\hspace{0.17em}5.79 ± 0.31}$ , and $\text{8.5 ± 2.5 \%}$ (estimated value), respectively. The total primary hot yield for organic products is $\text{26.1 ± 2.5 \%}$ , and that for all hot reactions including F‐to‐HF and F‐to‐F₂ abstraction is $\text{83 ± 3 \%}$ . There is no evidence in favor of hot F‐for‐2F or F‐for‐2H double substitution reactions in CH₃CF₃. Recoil ¹⁸F exhibits approximately a sixfold systematics preference for alkyl replacement reactions at the carbon—carbon bond in CH₃CF₃ relative to the average of substitution reactivities at carbon—fluorine and carbon—hydrogen bonds. The per‐bond preference for primary substitution reactions at carbon—hydrogen relative to carbon—fluorine bonds is $\text{2.30 ± 0.06}$ . The sums of primary hot yields for organic products are comparable for recoil ¹⁸F in CH₃CF₃ vs recoil ³H in alkanes, so that these two recoil systems differ principally in that ¹⁸F exhibits a preference for alkyl replacement reactions, whereas recoil ³H exhibits a preference for T‐for‐H substitution. All the organic products from primary ¹⁸F hot reactions exhibit extensive unimolecular decomposition.