Bypassing the multireference character of singlet molecular oxygen, part 1:1,4‐cyclo‐addition
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Bypassing the multireference character of singlet molecular oxygen, part 1:1,4‐cyclo‐addition. / Jespersen, Malte F.; Jørgensen, Solvejg; Johnson, Matthew S.; Mikkelsen, Kurt V.
I: International Journal of Quantum Chemistry, Bind 121, Nr. 6, e26523, 15.03.2021.Publikation: Bidrag til tidsskrift › Tidsskriftartikel › fagfællebedømt
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TY - JOUR
T1 - Bypassing the multireference character of singlet molecular oxygen, part 1:1,4‐cyclo‐addition
AU - Jespersen, Malte F.
AU - Jørgensen, Solvejg
AU - Johnson, Matthew S.
AU - Mikkelsen, Kurt V.
PY - 2021/3/15
Y1 - 2021/3/15
N2 - Modeling reactions involving singlet molecular oxygen (O2 [1Δg]) is challenging because the degeneracy of the highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO and LUMO) orbitals of oxygen causes a significant multireference character. Within the limit that singlet-singlet near-degeneracy disappears in the transition state, it would be possible to bypass singlet oxygen's multireference character by simply adding the experimentally determined singlet/triplet splitting (22.5 kcal/mol) to the energy of the triplet ground state of molecular oxygen. This method is tested by calculating rate constants for the reactions of singlet molecular oxygen with furan, 2-methylfuran, 2,5-dimethylfuran, pyrrole, 2-methylpyrrole, 2,5-dimethylpyrrole, and cyclopentadiene using transition state theory. We find that the reaction rate coefficients are within a factor of 15 of experimentally determined rate constants, indicating an error in the barrier energy of roughly 3 kcal/mol. Furthermore, we find that energy refinement at the CCSD(T)-F12 level of theory is crucial to achieving accurate results. We conclude that, based on a comparison with an experiment, this approximation is valid to some degree and can be used for other systems involving the 1,4-cyclo-addition of singlet oxygen.
AB - Modeling reactions involving singlet molecular oxygen (O2 [1Δg]) is challenging because the degeneracy of the highest occupied molecular orbital and lowest unoccupied molecular orbital (HOMO and LUMO) orbitals of oxygen causes a significant multireference character. Within the limit that singlet-singlet near-degeneracy disappears in the transition state, it would be possible to bypass singlet oxygen's multireference character by simply adding the experimentally determined singlet/triplet splitting (22.5 kcal/mol) to the energy of the triplet ground state of molecular oxygen. This method is tested by calculating rate constants for the reactions of singlet molecular oxygen with furan, 2-methylfuran, 2,5-dimethylfuran, pyrrole, 2-methylpyrrole, 2,5-dimethylpyrrole, and cyclopentadiene using transition state theory. We find that the reaction rate coefficients are within a factor of 15 of experimentally determined rate constants, indicating an error in the barrier energy of roughly 3 kcal/mol. Furthermore, we find that energy refinement at the CCSD(T)-F12 level of theory is crucial to achieving accurate results. We conclude that, based on a comparison with an experiment, this approximation is valid to some degree and can be used for other systems involving the 1,4-cyclo-addition of singlet oxygen.
U2 - 10.1002/qua.26523
DO - 10.1002/qua.26523
M3 - Journal article
VL - 121
JO - International Journal of Quantum Chemistry
JF - International Journal of Quantum Chemistry
SN - 0020-7608
IS - 6
M1 - e26523
ER -
ID: 257919915