• Bulletin of the Korean Chemical Society
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• v.33 no.12
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• pp.4079-4083
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• 2012

The mechanism of the cycloaddition reaction between singlet state dichlorosilylene germylidene ($Cl_2Si=Ge:$) and acetone has been investigated with B3LYP/6-$31G^*$ and B3LYP/6-$31G^{**}$ method, from the potential energy profile, we predict that the reaction has one dominant reaction pathway. The presented rule of the reaction is that the two reactants firstly form a Si-heterocyclic four-membered ring germylene through the [2+2] cycloaddition reaction. Because of the 4p unoccupied orbital of Ge atom in the Si-heterocyclic four-membered ring germylene and the ${\pi}$ orbital of acetone forming a ${\pi}{\rightarrow}p$ donor-acceptor bond, the Si-heterocyclic four-membered ring germylene further combines with acetone to form an intermediate. Because the Ge atom in the intermediate hybridizes to an $sp^3$ hybrid orbital after the transition state, then, the intermediate isomerizes to spiro-heterocyclic ring compound involving Si and Ge (P4) via a transition state.

• Journal of the Korean Chemical Society
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• v.65 no.1
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• pp.9-14
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• 2021

In this study, the DFT calculation was performed using the B3LYP/6-31G(d,p) basis sets for the reaction process in which phenanthrene decomposes due to the chain reaction of two OH radicals on phenanthrene in the gaseous state of 298 K at 1 atm. As a result of the calculation, even when two OH radicals act on phenanthrene in a chain, the reaction for producing phenanthren-9-ol is predicted to be more advantageous than the reaction for producing phenanthren-1-ol. On the other hand, it was predicted that the OH addition process at room temperature would be advantageous for the priority of the OH addition and H abstraction process.

• Bulletin of the Korean Chemical Society
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• v.35 no.3
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• pp.899-904
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• 2014

The atomic structures and electronic properties of six classical and nonclassical $H_2O$@$C_{24}$ fullerene regioisomers are systematically studied using the hybrid density functional B3LYP method and M06-2X method with empirical dispersion in conjunction with the 6-31G(d,p) basis sets. The charge transfer, frontier orbitals, dipole moment, energy gap between the HOMO and LUMO, and volume change of the $C_{24}$ cage are analyzed upon encapsulation of a $H_2O$ molecule in each $C_{24}$ regioisomer. All encapsulation processes are endothermic and the relative stabilities of six $C_{24}$ fullerene regioisomers change upon encapsulation of $H_2O$.

• Journal of the Korean Chemical Society
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• v.57 no.4
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• pp.461-471
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• 2013

Optimized geometrical structure, atomic charges, molecular electrostatic potential, nonlinear optical (NLO) effects and thermodynamic properties of the title compound N-(2,5-methylphenyl)salicylaldimine (I) have been investigated by using ab initio quantum chemical computational studies. Calculated results showed that the enol form of (I) is more stable than keto form. The solvent effect was investigated for obtained molecular energies, hardneses and the atomic charge distributions of (I). Natural bond orbital and frontier molecular orbital analysis of the title compound were also performed. The total molecular dipole moment (${\mu}$), linear polarizability (${\alpha}$), and first-order hyperpolarizability (${\beta}$) were calculated by B3LYP method with 6-31G(d), 6-31+G(d,p), 6-31++G(d,p), 6-311+G(d) and 6-311++G(d,p) basis sets to investigate the NLO properties of the compound (I). The standard thermodynamic functions were obtained for the title compound with the temperature ranging from 200 to 450 K.

• Bulletin of the Korean Chemical Society
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• v.25 no.4
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• pp.553-556
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• 2004

In this study we have performed ab initio computer simulations to investigate the conformational characteristics of the tetraethyl (1) and triethyl ester (2) of p-tert-butylcalix[4]arene. The structures of different conformational isomers for each compound have been optimized using ab initio RHF/6-31G methods. After optimization, B3LYP/6-31+G(d,p) single point calculations of the final structures are done to include the effect of electron correlation and the basis set with diffuse function and polarization function. Relative stability of tetraethyl ester (1) of p-tert-butylcalix[4]arene is in following order: cone (most stable) > partial cone > 1,3- alternate > 1,2-alternate isomer. Relative stability of triethyl ester (2) of p-tert-butylcalix[4]arene is in following order: cone (most stable) > 2-partial cone > 1-partial cone > 3-partial cone ~ 1,3-alternate ~ 1,2- alternate isomer.

• Bulletin of the Korean Chemical Society
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• v.34 no.10
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• pp.3022-3026
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• 2013

The adsorption of carbon dioxide on graphene sheets was theoretically investigated using density functional theory (DFT) and MP2 calculations. Geometric parameters and adsorption energies were computed at various levels of theory. The $CO_2$ chemisorption energies on graphene-$C_{40}$ assuming high pressure are predicted to be 71.2-72.1 kcal/mol for the lactone systems depending on various C-O orientations at the UCAM-B3LYP level of theory. Physisorption energies of $CO_2$ on graphene were predicted to be 2.1 and 3.3 kcal/mol, respectively, at the single-point $UMP2/6-31G^{**}$ level of theory for perpendicular and parallel orientations.

• Bulletin of the Korean Chemical Society
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• v.22 no.4
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• pp.395-400
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• 2001

The effects of ortho- (R = H and CH3) and Y-substituents (Y = OCH3, CH3H and CN), which are directly attached to the carbonyl carbon, on the protonation equilibria of the para-X-substituted benzoyl derivatives, 4-X -2, 6-di-R-C6H2-C(=O)-Y, are investigated theoretically using the B3LYP method with 6-31+G* basis set. Structurally, both of the (B) and (BH+ ) forms in the species with R = H are nearly coplanar regardless of the Y-substituents implying that the steric repulsion between Y-substituent and R = H is relatively small. In the species with R = CH3 , the tortional angle (Θ) between the carbonyl moiety and aryl ring varies from zero to near right angle depending on the degree of steric repulsion between Y and R = CH3 and the resonance demand. However the reaction energies, ΔG°, for the protonation processes are more favorable for R = CH3 than for R = H due to stronger electron donating effect of R = CH3 , although the species with R = CH3 are unfavorable sterically. On the other hand, the Hammett type plots are progressively better correlated with б+ than with б values on going from Y = OCH3 to Y = CN for both species with R = H and CH3 indicating that the degree of resonance delocalization between carbonyl moiety and X-substituent is increased for a more electron accepting Y-substituent. Nevertheless the effects of R = CH3 on the magnitude of Hammett type reaction constants ( б or б+ ) are not much different from those of R = H.

• Journal of the Korean Chemical Society
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• v.63 no.3
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• pp.151-159
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• 2019

The TADF properties for carbazol-dicyanobenzene, carbazol-diphenyl sulfone, carbazol-benzonitrile derivatives as OLED candidate materials are theoretically investigated using density functional theory (DFT) with $6-31G^{**}$, cc-pVDZ, and cc-pVTZ basis sets. The optimized geometries, harmonic vibrational frequencies, and HOMO-LUMO energy separations are predicted at the B3LYP/$6-31G^{**}$ level of theory. The harmonic vibrational frequencies of the molecules considered in this study show all real numbers implying true minima. The time dependent density functional theory (TD-DFT) calculations have been also applied to investigate the absorption and emission wavelength (${\lambda}_{max}$), energy differences (${\Delta}E_{ST}$) between excited singlet ($S_1$) and triplet ($T_1$) states of candidate materials.

• Bulletin of the Korean Chemical Society
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• v.25 no.12
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• pp.1911-1916
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• 2004

The conformational preference of tetrahomodioxacalix[4]arenes with three different para substituents on the phenolic ring has been investigated by using ab initio molecular orbital theory (RHF/6-31$G^{\ast}$) and density functional theory (B3LYP/6-31$G^{\ast}$). The stability order is predicted to be cone > C-1,2-alternate > partial cone > 1,3-alternate > COC-1,2-alternate. The distorted cone conformation is found to be most stable in a gas phase and the calculated results are in agreement with the reported $^1$H NMR and X-ray experimental observations. The substitution of methylene with dimethyleneoxa bridges increases the size of the annulus of the molecule, its conformational mobility, and the number of hydrogen bonding patterns. The thermodynamic stability and the conformational characteristics of tetrahomodioxacalix[4]arenes are discussed in regards of the number of phenolic hydrogen bonding patterns and the polarity of a molecule. The substituent effects on the para position of the phenolic ring are also introduced.

• Journal of the Korean Chemical Society
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• v.42 no.6
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• pp.629-637
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• 1998

The HF-SCF, MP2 and B3LYP calculations have been performed on the two conceivable clusters $(HF)_2(CO)$ trimers as well as their dimer complexes FH…FH, FH…CO and FH…OC applying $6-31+G^{\ast}^{\ast}$, and $6-311+G^{\ast}^{\ast}$ basis sets. A variety of ground state properties of these trimer complexes have been listed, and compared with corresponding properties of isolated monomers and combined dimers. It was calculated that FH…CO is more stable than FH…OC by average 0.85 kcal/mol and F-H…F-H…C≡O is more stable than F-H…F-H…O≡C by 1-2 kcal/mol. The C≡O stretching bands of the F-H…F-H…C≡O and F-H…F-H…O≡C were red shifted by 24, $37\;cm^{-1}$ compared with the FH…CO and FH…OC respectively. Also, H-F stretching bands were red shifted by 54 and $353\;cm^{-1}$.