One-electron reduction of substituted chlorinated methanes as determined from ab initio electronic structure theory

Eric J. Bylaska, David A. Dixon, Andrew R. Felmy, Paul Tratnyek

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17 Citations (Scopus)

Abstract

Substituted chloromethyl radicals and anions are potential intermediates in the reduction of substituted chlorinated methanes (CHxCl3-xL, with L- = F-, OH-, SH-, NO3 -, HCO3 - and x = 0-3). Thermochemical properties, ΔHf °(298.15 K), S°(298.15 K,1 bar), and ΔGs(298.15 K, 1 bar), were calculated by using ab initio electronic structure methods for the substituted chloromethyl radicals and anions: CHyCl2-yL· and CHyCl2-yL-, for y = 0-2. In addition, thermochemical properties were calculated for the aldehyde, ClHCO, and the gem-chlorohydrin anions, CCl3O-, CHCl2O-, and CH2ClO-. The thermochemical properties of these additional compounds were calculated because the nitrate-substituted compounds, CHyCl2-y(NO3)· and CHyCl2-y(NO3)-, were not stable, with all levels of ab initio theory leading to highly dissociated complexes. On the basis of these thermochemical estimates, the overall reaction energetics (in the gas phase and aqueous phase) for several mechanisms of the first electron reduction of the substituted chlorinated methanes were predicted. In almost all of the cases, the thermodynamically most favorable pathway resulted in loss of Cl-. The exception was for the reduction of the nitrate-substituted chlorinated methanes CHxCl3-x(NO3). On reduction, these compounds were shown to readily decompose into a Cl- anion, NO2· gas, and an aldehyde. In addition, the results of this study suggest that a higher degree of chlorination corresponds to a more favorable reduction. Relative to the nonsubstituted chlorinated methanes, the thermodynamic results suggest the CHxCl3-xF, CHxCl3-xOH, and CHxCl3-x(HCO3) compounds are moderately more difficult to reduce, the CHxCl3-xSH compounds are moderately less difficult to reduce, and the CHxCl3-x(NO3) compounds are substantially more favorable to reduce. These results demonstrate that ab initio electronic structure methods can be used to calculate the reduction potentials of organic compounds to help identify the potentially important environmental degradation reactions.

Original languageEnglish (US)
Pages (from-to)11581-11593
Number of pages13
JournalJournal of Physical Chemistry A
Volume106
Issue number47
DOIs
StatePublished - Nov 28 2002

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Methane
Electronic structure
thermochemical properties
methane
electronic structure
Anions
Electrons
anions
electrons
aldehydes
nitrates
Aldehydes
Nitrates
Chlorohydrins
Gases
chlorination
Gems
organic compounds
Chlorination
Weathering

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

One-electron reduction of substituted chlorinated methanes as determined from ab initio electronic structure theory. / Bylaska, Eric J.; Dixon, David A.; Felmy, Andrew R.; Tratnyek, Paul.

In: Journal of Physical Chemistry A, Vol. 106, No. 47, 28.11.2002, p. 11581-11593.

Research output: Contribution to journalArticle

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abstract = "Substituted chloromethyl radicals and anions are potential intermediates in the reduction of substituted chlorinated methanes (CHxCl3-xL, with L- = F-, OH-, SH-, NO3 -, HCO3 - and x = 0-3). Thermochemical properties, ΔHf °(298.15 K), S°(298.15 K,1 bar), and ΔGs(298.15 K, 1 bar), were calculated by using ab initio electronic structure methods for the substituted chloromethyl radicals and anions: CHyCl2-yL· and CHyCl2-yL-, for y = 0-2. In addition, thermochemical properties were calculated for the aldehyde, ClHCO, and the gem-chlorohydrin anions, CCl3O-, CHCl2O-, and CH2ClO-. The thermochemical properties of these additional compounds were calculated because the nitrate-substituted compounds, CHyCl2-y(NO3)· and CHyCl2-y(NO3)-, were not stable, with all levels of ab initio theory leading to highly dissociated complexes. On the basis of these thermochemical estimates, the overall reaction energetics (in the gas phase and aqueous phase) for several mechanisms of the first electron reduction of the substituted chlorinated methanes were predicted. In almost all of the cases, the thermodynamically most favorable pathway resulted in loss of Cl-. The exception was for the reduction of the nitrate-substituted chlorinated methanes CHxCl3-x(NO3). On reduction, these compounds were shown to readily decompose into a Cl- anion, NO2· gas, and an aldehyde. In addition, the results of this study suggest that a higher degree of chlorination corresponds to a more favorable reduction. Relative to the nonsubstituted chlorinated methanes, the thermodynamic results suggest the CHxCl3-xF, CHxCl3-xOH, and CHxCl3-x(HCO3) compounds are moderately more difficult to reduce, the CHxCl3-xSH compounds are moderately less difficult to reduce, and the CHxCl3-x(NO3) compounds are substantially more favorable to reduce. These results demonstrate that ab initio electronic structure methods can be used to calculate the reduction potentials of organic compounds to help identify the potentially important environmental degradation reactions.",
author = "Bylaska, {Eric J.} and Dixon, {David A.} and Felmy, {Andrew R.} and Paul Tratnyek",
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T1 - One-electron reduction of substituted chlorinated methanes as determined from ab initio electronic structure theory

AU - Bylaska, Eric J.

AU - Dixon, David A.

AU - Felmy, Andrew R.

AU - Tratnyek, Paul

PY - 2002/11/28

Y1 - 2002/11/28

N2 - Substituted chloromethyl radicals and anions are potential intermediates in the reduction of substituted chlorinated methanes (CHxCl3-xL, with L- = F-, OH-, SH-, NO3 -, HCO3 - and x = 0-3). Thermochemical properties, ΔHf °(298.15 K), S°(298.15 K,1 bar), and ΔGs(298.15 K, 1 bar), were calculated by using ab initio electronic structure methods for the substituted chloromethyl radicals and anions: CHyCl2-yL· and CHyCl2-yL-, for y = 0-2. In addition, thermochemical properties were calculated for the aldehyde, ClHCO, and the gem-chlorohydrin anions, CCl3O-, CHCl2O-, and CH2ClO-. The thermochemical properties of these additional compounds were calculated because the nitrate-substituted compounds, CHyCl2-y(NO3)· and CHyCl2-y(NO3)-, were not stable, with all levels of ab initio theory leading to highly dissociated complexes. On the basis of these thermochemical estimates, the overall reaction energetics (in the gas phase and aqueous phase) for several mechanisms of the first electron reduction of the substituted chlorinated methanes were predicted. In almost all of the cases, the thermodynamically most favorable pathway resulted in loss of Cl-. The exception was for the reduction of the nitrate-substituted chlorinated methanes CHxCl3-x(NO3). On reduction, these compounds were shown to readily decompose into a Cl- anion, NO2· gas, and an aldehyde. In addition, the results of this study suggest that a higher degree of chlorination corresponds to a more favorable reduction. Relative to the nonsubstituted chlorinated methanes, the thermodynamic results suggest the CHxCl3-xF, CHxCl3-xOH, and CHxCl3-x(HCO3) compounds are moderately more difficult to reduce, the CHxCl3-xSH compounds are moderately less difficult to reduce, and the CHxCl3-x(NO3) compounds are substantially more favorable to reduce. These results demonstrate that ab initio electronic structure methods can be used to calculate the reduction potentials of organic compounds to help identify the potentially important environmental degradation reactions.

AB - Substituted chloromethyl radicals and anions are potential intermediates in the reduction of substituted chlorinated methanes (CHxCl3-xL, with L- = F-, OH-, SH-, NO3 -, HCO3 - and x = 0-3). Thermochemical properties, ΔHf °(298.15 K), S°(298.15 K,1 bar), and ΔGs(298.15 K, 1 bar), were calculated by using ab initio electronic structure methods for the substituted chloromethyl radicals and anions: CHyCl2-yL· and CHyCl2-yL-, for y = 0-2. In addition, thermochemical properties were calculated for the aldehyde, ClHCO, and the gem-chlorohydrin anions, CCl3O-, CHCl2O-, and CH2ClO-. The thermochemical properties of these additional compounds were calculated because the nitrate-substituted compounds, CHyCl2-y(NO3)· and CHyCl2-y(NO3)-, were not stable, with all levels of ab initio theory leading to highly dissociated complexes. On the basis of these thermochemical estimates, the overall reaction energetics (in the gas phase and aqueous phase) for several mechanisms of the first electron reduction of the substituted chlorinated methanes were predicted. In almost all of the cases, the thermodynamically most favorable pathway resulted in loss of Cl-. The exception was for the reduction of the nitrate-substituted chlorinated methanes CHxCl3-x(NO3). On reduction, these compounds were shown to readily decompose into a Cl- anion, NO2· gas, and an aldehyde. In addition, the results of this study suggest that a higher degree of chlorination corresponds to a more favorable reduction. Relative to the nonsubstituted chlorinated methanes, the thermodynamic results suggest the CHxCl3-xF, CHxCl3-xOH, and CHxCl3-x(HCO3) compounds are moderately more difficult to reduce, the CHxCl3-xSH compounds are moderately less difficult to reduce, and the CHxCl3-x(NO3) compounds are substantially more favorable to reduce. These results demonstrate that ab initio electronic structure methods can be used to calculate the reduction potentials of organic compounds to help identify the potentially important environmental degradation reactions.

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