Activation Parameters for the Additions of Arylhalocarbenes to Alkenes

Article abstract of DOI:10.1021/ja00282a030

By use of nanosecond laser flash photolytic methods, absolute rate constants have been obtained for the additions of p-(trifluoromethyl)phenylbromocarbene (CF3C6H4CBr), phenylbromocarbene (PhCBr), phenylchlorocarbene (PhCCl), phenylfluorocarbene (PhCF), and p-methoxyphenylfluorocarbene (CH3OC6H4CF) to tetramethylethylene (TME) and 1-hexene.The rate constants ranged from 1.7 x 10⁹ (CF3C6H4CBr/TME) to 5.0 x 10⁴ L/(M.s) (CH3OC6H4CF)/1-hexene); classical structure/reactivity relations were obeyed.Determination of the rate constants at temperatures between 315 and 200 K gave E_a, logA, ΔH*, ΔS*, and ΔG* for the 10 reactions.All of thereactions were dominated by ΔS*, ΔG* ranged from 5.0 to 11 kcal/mol for the fastest and slowest reactions.Negative values of E_a were observed some of the faster reactions at higher temperatures.These results are analyzed in terms of single-step addition reactions where ΔG* is dominated by ΔS* and, alternatively, in terms of a two-steps machanism proceeding through a carbene-alkene complex.