TY - JOUR
T1 - Ab initio molecular orbital theory on intramolecular charge polarization
T2 - Effect of hydrogen abstraction on the charge sensitivity of aromatic and nonaromatic species
AU - Morita, Akihiro
AU - Kato, Shigeki
PY - 1997/4/30
Y1 - 1997/4/30
N2 - We performed ab initio molecular orbital (MO) calculations of the response kernel (δQ(a)/δV(b)), which represents the response of the intramolecular charge polarization by external electrostatic field, on the basis of the coupled perturbed Hartree-Fock equation. The response kernels of some organic molecules including pyrazine, pyrazinyl radical, acetone, and 2- hydroxypropyl radical were calculated along the present formulation. The results revealed that the hydrogen abstraction of pyrazine causes the product radical to be remarkably deformable in the partial charge distribution, while the hydrogen abstraction of acetone does not induce such enhancement of the charge sensitivity. The augmented sensitivity does not appear in the usual polarizability for a uniform field but emerges for a local fluctuated field. To elucidate the remarkable difference, we performed the normal mode analysis and decomposition based on the intrinsic soft MO pairs or localized orbitals. As a result, the enhancement in the aromatic species is attributed to the softest normal mode due to the π-σ mixing that facilitates the deformation of the π-electron orbitals. In the nonaromatic species, on the other hand, this effect is not dominant and is canceled by the breakdown of hyperconjugation. We suggest that the particular sensitivity of aromatic radicals is the origin of anomalously slow diffusion in solution.
AB - We performed ab initio molecular orbital (MO) calculations of the response kernel (δQ(a)/δV(b)), which represents the response of the intramolecular charge polarization by external electrostatic field, on the basis of the coupled perturbed Hartree-Fock equation. The response kernels of some organic molecules including pyrazine, pyrazinyl radical, acetone, and 2- hydroxypropyl radical were calculated along the present formulation. The results revealed that the hydrogen abstraction of pyrazine causes the product radical to be remarkably deformable in the partial charge distribution, while the hydrogen abstraction of acetone does not induce such enhancement of the charge sensitivity. The augmented sensitivity does not appear in the usual polarizability for a uniform field but emerges for a local fluctuated field. To elucidate the remarkable difference, we performed the normal mode analysis and decomposition based on the intrinsic soft MO pairs or localized orbitals. As a result, the enhancement in the aromatic species is attributed to the softest normal mode due to the π-σ mixing that facilitates the deformation of the π-electron orbitals. In the nonaromatic species, on the other hand, this effect is not dominant and is canceled by the breakdown of hyperconjugation. We suggest that the particular sensitivity of aromatic radicals is the origin of anomalously slow diffusion in solution.
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U2 - 10.1021/ja9635342
DO - 10.1021/ja9635342
M3 - Article
AN - SCOPUS:0030908729
VL - 119
SP - 4021
EP - 4032
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 17
ER -