Thymine, molecular orbitals, energy

Snyder et ai.364 have also calculated the molecular orbital energies of anionic forms of thymine by ab initio method. b Mainly localized on 0-7. 

Compare the following papers for the discussion of the energies of occupied and unoccupied molecular orbitals of uracil and thymine, and of their complexes with different partners uracil,171 173 I77 178 182 200 201 203 ao7 a89 280 407 41a thymine,171 184 186,201,260 adenine-thymine,la4 186 190 208 2-NH2-purine-thymine,190 uracil-uracil, uracil-uracil-uracil, thymine-thymine, and thymine-thymine-thymine.171... 

The energies of the molecular orbitals of the adenine-thymine base pair have been calculated by several authors to elucidate the effect of hydrogen bond formation on the properties of the bases (for u-HMO calculations, see refs. 1, 140, 171, 263). 

Energies of Highest Occupied (HOMO) and Lowest Empty (LEMO) Molecular Orbitals of Adenine, Thymine, and Their Pair Calculated by w-SCF MO Method (Closed-Shell)"... 

Figure 20-5. Molecular orbital plots of neural 5 -dTMPH, calculated using the B3LYP/6-31G method. B3LYP/6-31G calculated orbital energies along with scaled values are given in eV. In parentheses the experimental VOEs of thymine (Ref. [94]) are given in eV. (Reprinted with permission from ref. [209], J. Phys. Chem. (2007) American Chemical Society.)...

From ETS experiments (Aflatooni et al. 1998), Aflatooni et al. showed that energies required to attach an electron into the lowest empty valence molecular orbitals of all the bases are positive. This means that all the bases have negative valence vertical electron affinity (<0). The vertically formed anions of pyrimidines bases (C, T, and U) were found to be more stable than the purines (G and A) by ca. 0.2 eV. The ETS spectra of U, T, C, G, and A are shown in O Fig. 34-7. The spectra in O Fig. 34-7 arise due to the occupation of the lowest empty 7t -MOs of the parent molecules by the electron. The vertical lines on the spectra (O Fig. 34-7) show the position of the vertical attachment energies. For guanine anion, the ETS (shown in O Fig. 34-7) was observed for its enol tautomer (for details see Aflatooni et al. [1998]). For each of these molecules, three VAEs, associated with the three lowest vacant tTi, tT2, and 7T3 MOs, were determined. The VAEs 0.22,1.58, and 3.83 eV for uracil 0.29,1.71, and 4.05 eV for thymine 0.32,1.53, and 4.50 eV for cytosine 0.54,1.36, and 2.17 eV for adenine and 0.46,1.37, and 2.36 eV for guanine(enol) tautomer were determined by ETS. 

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