Kinetic and thermodynamic parameters of three-electron bonded species formed on reaction of hydroxyl radicals with alkyl iodides and 1,n-diiodoalkanes

Abstract

The reaction of hydroxyl radicals with n-alkyl iodides and 1,n-diiodoalkanes (n = 1 to 5) has been studied. Nanosecond pulse radiolysis experiments have been performed to find out the stability constants of the dimer radical cations of the alkyl iodides in acid aqueous solution. The bond enthalpy and entropy for the intermolecular two-centre three-electron bond in ethyl iodide and intramolecular two-centre three-electron bond in 1,4-diiodobutane are determined by means of temperature dependent kinetic studies. Quantum chemical computations have been performed to study the reaction of OH radicals with n-alkyl iodides and 1,n-diiodoalkanes (n = 1 to 5) theoretically. The semiempirical quantum chemical calculation (UHF/AM1) shows that the reaction of hydroxyl radicals (OH) with ethyl iodide (CH₃CH₂I) and 1,2-diiodoethane (ICH₂CH₂I) leads to the formation of three electron bonded adducts (RI∴OH) which are bound by ∼10 kcal mol⁻¹. The inter- and intramolecular two-centre three-electron bond strengths in the respective radical cations are also calculated and good correlation is observed between experimental and calculated results.