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Probing the Cyclic Transition State in the Reaction O(3P) + Alkyl Iodides to Form HOI: Electronic, Steric and Thermodynamic Factors Influencing the Reaction Pathway



J P. Reid, C X. Qian, S R. Leone


Electronic, steric and thermodynamic factors governing the reaction of O[3P) with alkyl iodides to yield HOI are probed by time-resolved Fourier transform infrared emission spectroscopy. The reaction to produce HOI is known to proceed through a cyclic-5-membered transition state. Steric effects are examined by studying the nascent vibrational distribution of the HOI product in the reactions of O[3P] with cyclopentyl iodide and cyclohexyl iodide. Little effect of steric hindrance is observed with either of these reactants. A CF3 electron withdrawing group on the carbon in the Β-position to the iodine atom, probed by studying the precursor CH2ICH2CF3, weakens the C-H bond participating in the cyclic transition state and therefore diminishes the partitioning of vibrational energy into the HOI product. The cyclic 5-membered transition state occurs not only with saturated hydrocarbon chains, but also when either the H atom or the I atom is abstracted fro an olefinic carbon site to yield an allene or acetylene product. This is explored by probing the reactions of O(3)) with CH2+CHI and CH2+CHCH2I, vinyl and allyl iodide, respectively. The energetic driving force for these reactions is the formation of the carbon-carbon multiple bond in the corresponding product. If a strongly doubly bound product pathway is not available, such as in the reaction of O(3P) with trimethyliodosilane, (CH3)3Sil, the reaction exothermicity is not sufficient to form vibrationally excited HOI. Preferential reaction through a 5-membered cyclic transition state to abstract an H atom from a carbon atom, rather than through a 6-membered ring by abstraction of an H atom from an oxygen atom, appears to be the mechanism in the reaction of O(3P) with 2-iodoethanol, CH2ICH2OH.
Physical Chemistry Chemical Physics
No. 4


cyclic transition state, gas phase reaction dynamics, time-re-solved spectroscopy


Reid, J. , Qian, C. and Leone, S. (2000), Probing the Cyclic Transition State in the Reaction O(<sup>3</sup>P) + Alkyl Iodides to Form HOI: Electronic, Steric and Thermodynamic Factors Influencing the Reaction Pathway, Physical Chemistry Chemical Physics (Accessed March 4, 2024)
Created January 31, 2000, Updated October 12, 2021