Benchmark thermochemistry of chloramines, bromamines, and bromochloramines: halogen oxidants stabilized by electron correlation

Abstract

Chloramines, bromamines, and bromochloramines are halogen-containing oxidants that arise from the reaction of hypohalous acids with ammonia in water. Although relevant to both water disinfection chemistry and biochemistry, these molecules are difficult to study in the laboratory, and their thermochemical properties remain poorly established. We developed a benchmark level ab initio calculation protocol, termed TA14, adapted from the Weizmann theory and Feller-Peterson-Dixon approaches to determine the molecular structures and thermochemical properties of these compounds. We find that the halamine molecules are bound largely, and in some cases entirely, by electron correlation forces. This presumably explains their high reactivity as electrophilic oxidants. We provide computed heats of formation at 0 K (ΔfH(0)(0 K)) and at 298 K (ΔfH(0)(298 K)) and Gibbs free energies of formation at 298 K (ΔfG(0)(298 K)) for the 9 inorganic chloramines, bromamines, bromochloramines in gas phase. Based on comparisons to previous theoretical and experimental data for a set of 11 small molecules containing N, O, H, Cl, and Br, we propose uncertainties ranging from 1 to 3 kJ mol(-1) for computed thermodynamic properties of the halamines. Reported thermochemical data enable the determination of equilibrium constants for reactions involving halamines, opening possibilities for more quantitative studies of the chemistry of these poorly understood compounds.

Gas-Phase Ozone Reactions with a Structurally Diverse Set of Molecules: Barrier Heights and Reaction Energies Evaluated by Coupled Cluster and Density Functional Theory Calculations

“…Diagnostics for nondynamical correlation effects can give an indication of the importance of post-CCSD­( T ) electronic contributions for thermochemical applications. ,, A comparison of multireference diagnostics between RHF- and UHF-based CC calculations should give some additional insight into whether one type of reference wave function should be preferred in energy calculations. We calculated the T1 diagnostic and the %TAE­[( T )] diagnostic for all species involved in all reactions, shown in Table S19 in the Supporting Information, along with the spin contamination of the UHF reference.…”

Heterocycles Derived from Generating Monovalent Pnictogens within NCN Pincers and Bidentate NC Chelates: Hypervalency versus Bell-Clappers versus Static Aromatics

“…Given the impracticality associated with handling chlorinated amine derivatives, we devised an alternative route to nitrogen counterpart 5 . Lithiation of A (R = Mes, R′ = Me) with n -BuLi, followed by treatment with the electrophilic nitrogen source TsN 3 led to the in situ generation of (NCN)–N 3 , which extruded N 2 upon heating (100 °C) to afford 5 as a colorless oil in 62% yield (Scheme ).…”

Large-scale calculations of gas phase thermochemistry: Enthalpy of formation, standard entropy, and heat capacity

“…These results are in agreement with other studies showing that energetics for molecules containing heavy or electron-withdrawing elements are not predicted accurately. 48,49 For instance, it has been shown that CCSD(T) with extrapolation to the complete basis-set limit, combined with the core valence correlation and relativistic effects, is needed to improve the accuracy of thermochemistry for chlorine containing molecules. 49 Moreover, it has been observed that halogen-containing molecules are severely affected by a nondynamical electron correlation; thus, a post-CCSD(T) correlation treatment may be needed.…”

“…48,49 For instance, it has been shown that CCSD(T) with extrapolation to the complete basis-set limit, combined with the core valence correlation and relativistic effects, is needed to improve the accuracy of thermochemistry for chlorine containing molecules. 49 Moreover, it has been observed that halogen-containing molecules are severely affected by a nondynamical electron correlation; thus, a post-CCSD(T) correlation treatment may be needed. 48 For large molecules such as fatty acids and esters, a parametric empirical correction equation-based on the number of bonding, core and unpaired electrons in the ground state-has been derived in order to correct the quantum enthalpy of formation.…”