TY - JOUR
T1 - Reductive dechlorination of trichloroethylene
T2 - A computational study
AU - Nonnenberg, Christel
AU - Van der Donk, Wilfred A.
AU - Zipse, Hendrik
PY - 2002/9/19
Y1 - 2002/9/19
N2 - Vitamin B12 catalyzes the reductive dechlorination of several ubiquitous pollutants including the conversion of trichloroethylene (TCE) to ∼95% cis-1,2-dichloroethylene (DCE) and small amounts of trans-DCE and 1,1-DCE. The origins of this unexpected selectivity were investigated using density functional and coupled-cluster theory. At all levels of theory considered, the initially formed trichloroethylene radical anion is an unstable species. Breakage of one of the three C-Cl bonds during the dissociative process gives the most stable ion complex when the two remaining chlorines occupy a cis geometry. Once formed, the cis-1,2-dichloroethen-1-y1 radical is about 6 kJ/mol more stable than the corresponding trans radical and 21 kJ/mol more stable than the 1,1-dichloroethen-2-yl radical. The calculated relative energies can be rationalized by delocalization of the unpaired electron over the nonbonding orbitals of the α-chlorine. The computed geometries of the radicals suggest significant interactions between the orbital occupied by the unpaired electron and the σ* orbital of the β C-Cl bond trans to the radical. The barrier for interconversion of the two 1,2-dichlorinated vinyl radicals lies between ∼30-40 kJ/mol depending on the level of theory. The reactivities of the three radicals with respect to hydrogen atom abstraction from methanol (C-H or O-H) as well as chlorine elimination were investigated. All three radicals show a strong preference for abstraction of the α-hydrogen atom of methanol (17-25 kJ/mol), with a significant positive reaction energy for chlorine elimination (60-80 kJ/mol). These results are discussed further in relation to the experimentally observed product distribution.
AB - Vitamin B12 catalyzes the reductive dechlorination of several ubiquitous pollutants including the conversion of trichloroethylene (TCE) to ∼95% cis-1,2-dichloroethylene (DCE) and small amounts of trans-DCE and 1,1-DCE. The origins of this unexpected selectivity were investigated using density functional and coupled-cluster theory. At all levels of theory considered, the initially formed trichloroethylene radical anion is an unstable species. Breakage of one of the three C-Cl bonds during the dissociative process gives the most stable ion complex when the two remaining chlorines occupy a cis geometry. Once formed, the cis-1,2-dichloroethen-1-y1 radical is about 6 kJ/mol more stable than the corresponding trans radical and 21 kJ/mol more stable than the 1,1-dichloroethen-2-yl radical. The calculated relative energies can be rationalized by delocalization of the unpaired electron over the nonbonding orbitals of the α-chlorine. The computed geometries of the radicals suggest significant interactions between the orbital occupied by the unpaired electron and the σ* orbital of the β C-Cl bond trans to the radical. The barrier for interconversion of the two 1,2-dichlorinated vinyl radicals lies between ∼30-40 kJ/mol depending on the level of theory. The reactivities of the three radicals with respect to hydrogen atom abstraction from methanol (C-H or O-H) as well as chlorine elimination were investigated. All three radicals show a strong preference for abstraction of the α-hydrogen atom of methanol (17-25 kJ/mol), with a significant positive reaction energy for chlorine elimination (60-80 kJ/mol). These results are discussed further in relation to the experimentally observed product distribution.
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U2 - 10.1021/jp0264073
DO - 10.1021/jp0264073
M3 - Article
AN - SCOPUS:0037136630
SN - 1089-5639
VL - 106
SP - 8708
EP - 8715
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 37
ER -