• Bulletin of the Korean Chemical Society
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• v.10 no.4
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• pp.346-348
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• 1989

Interactions between Tl atoms for the Tl dimer are studied by relativistic and nonrelativistic EHT methods. Relativistic bond weakening for the Tl dimer is qualitatively explained by comparing orbital energies from relativistic and nonrelativistic calculations. It is also shown that significant overlap exists, especially for 6p orbitals, at the internuclear distance larger than 4 ${\AA}$, implying that Tl-Tl interaction is not just the electrostatic interaction in the recently discovered dimeric thallacarborane.

• Bulletin of the Korean Chemical Society
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• v.29 no.2
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• pp.305-308
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• 2008

We performed coupled-cluster calculations to determine the intermolecular interaction energy between two TiAu4 clusters. Our ab initio calculations predict that the binding energy is 2.89 eV, which is somewhat larger than the known binding energy of 2.0 eV for TiH4-TiH4. The intermolecular binding energy is relatively high, despite TiAu4 having all the attributes of a magic cluster. The favorable orbital interaction between occupied Au(6s) and unoccupied Ti(3d) orbitals leads to the strong dimeric interaction for TiAu4-TiAu4.

• Bulletin of the Korean Chemical Society
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• v.23 no.2
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• pp.201-204
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• 2002

The rates of the aminolysis of S-phenyl substituted-acetate series $(RC(=O)SC_6H_4Z$, with R=Me, Et, i-Pr, t-Bu and Bn) with benzylamines $(XC_6H_4CH_2NH_2)$ are not correlated simply with the Taft's polar $({\sigma}^{\ast})$ and/or steric effect constants $(E_s)$ of the substituents due to abnormally enhanced rate of the substrate with R=Et. Furthermore, the cross-interaction constant, ${\rho}x_z$ , is the largest with R=Et. These anomalous behaviors can only be explained by invoking the vicinal bond $({\sigma})$-antibond $({\sigma}^{\ast})$ charge transfer interaction between C-$C{\alpha}$ and C-S bonds. In the tetrahedral zwitterionic intermediate, $T^{\pm}$ , formed with R=Et the vicinal ${\sigma}_{c-c}-{\sigma}^{\ast}_{c-s}$ delocalization is the strongest with an optimum antiperiplanar arrangement and a narrow energy gap, ${\Delta}{\varepsilon}={\varepsilon}_{{\sigma}^{\ast}}-{\varepsilon}_{\sigma}$. Due to this charge transfer interaction, the stability of the intermediate increases (with the concomitant increase in the equilibrium constant K (= $k_a/k_{-a}$)) and also the leaving ability of the thiophenolate leaving group increases (and hence $k_b$ increases) so that the overall rate, $k_n\;=\;Kk_b$, is strongly enhanced. Theoretical support is provided by the natural bond orbital (NBO) analyses at the B3LYP/6-31+$G^{\ast}$ level. The anomaly exhibited by R=Et attests to the stepwise reaction mechanism in which the leaving group departure is rate limiting.

• Journal of the Korean Chemical Society
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• v.13 no.4
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• pp.273-280
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• 1969

The MO's of maleic anhydride are calculated using the parameter values, $h_{o}$.= 1, $h_{o}$:= 2, $k_{c=o}$= 1, $k_{c-o}$= 0.8, and ${\delta}_{{\alpha}_n}=2{\times}(0.3)^n$. With these MO's the interaction energies of the photochemical reaction of maleic anhydride (MA) with benzene are calculated using intermolecular orbital theory. It is shown that there are cases where the interaction energy includes a constant term and this term takes a great role in the photochemical interaction energy, and that with the calculated interaction energies the reaction mechanism is quite well explained. And it is proved that the photochemical reaction is possible for the second addition step of MA to benzene, and that the MA-benzene adduct should have the well-known stereochemical structure.

• Journal of the Korean Chemical Society
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• v.29 no.2
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• pp.98-103
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• 1985

Orbital interactions between two nonbonding orbitals have been investigated for heteroatom analogues of trimethylene diradical using MINDO/3 and STO-3G methods. The results showed that the conformers in which significant ${\sigma}$-aromatic stabilization is involved exhibited level order reversal to $n_-$ below $n_+$ as it was found for trimethylene diradical. Lone pair orbitals (LPO) were found to be stabilized by charge dispersion accompanying vicinal trans $n-{\sigma}^*$ interaction and hydrogen bonding. In systems with different heteroatoms, N and O, the contribution of the LPO of oxygen, $n_O$ was always greater in the lower level whereas that of nitrogen, nN, was greater in the higher level as can be expressed as : $n_{\pm}$(lower) = $n_O{\pm}{\lambda}_Nn_N.\;n_{\pm}(higher)\;=\;n_N{\pm}{\lambda}_On_O$. where ${\lambda}_i$< 1.0

• Bulletin of the Korean Chemical Society
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• v.23 no.2
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• pp.221-224
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• 2002

Nucleophilic addition reactions of benzylamines (BA; $XC_6H_4CH_2NH_2$) to ethyl-${\alpha}$-cyanocinnamates (ECC;$YC_6H_4CH$=C(CN)COOEt) have been investigated in acetonitrile at $30.0^{\circ}C$. The rate is first order with respect to BA and ECC. The rate is slower than that expected from the additive effect of ${\sigma}^-$ or $R^-$ for the activating groups (CN and COOEt). Natural. bond orbital ${\pi}^{\ast}_{c=c}$ calculations show that the contribution of COOEt group may not be fully effective despite the coplanar molecular structure. The selectivity parameters including the cross-interaction constant (${\rho}_{xy}$ = -0.22) indicate that the addition occurs in a single step. The kinetic isotope effects ($k_H/k_D$=2.5-2.8) involving deuterated BA ($XC_6H_4CH_2ND_2$) nucleophiles and activation parameters (${\Delta}H^{\neq}=4{\sim}6\;kcal\;mol^{-1};{\Delta}S^{\neq}=-45{\sim}-52\;e.u.$) suggest a cyclic transition state in which N-$C_{\alpha}$ and H-$C_{\beta}$ bonds are formed concurrently.

• Journal of the Korean Magnetics Society
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• v.26 no.4
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• pp.119-123
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• 2016

We have studied electronic and magnetic structure of cubane-type Cu magnetic molecule using density functional method. The calculated density of states show that Cu has 3d $x^2-y^2$ hole orbital because of short distances between Cu atom and in-plane 4 ligand atoms. The calculated total energy with in-plane antiferromagnetic spin configuration is lower than those of ferromagnetic configurations. The calculated exchange interaction J between in-plane Cu atoms is much larger than those between out-plane Cu atoms, since the $x^2-y^2$ hole orbital ordering of Cu 3d orbitals induces strong super-exchange interaction between in-plane Cu atoms.

• Journal of the Korean Physical Society
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• v.73 no.11
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• pp.1691-1697
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• 2018

Employing the density functional theory, we have investigated the roles of Coulomb and Hund's interactions in the electronic and magnetic properties of newly discovered ${\alpha}-RuCl_3$ having the $R{\overline{3}}$ symmetry, which is in close proximity of the Kitaev system. We show that both the size and the direction of local magnetic moment are highly dependent on Coulomb and Hund's interactions, and the spin and orbital parts show different behaviors. The validity of the so-called $j^{eff}$ picture is accessed upon interaction parameters, and the explicit roles of Hund's interaction in the local electronic structures and magnetic properties are discussed.

• Bulletin of the Korean Chemical Society
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• v.34 no.12
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• pp.3727-3732
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• 2013

The interaction between metalloporphyrins and diazine tautomers was investigated using quantum chemistry method. The results showed that the metal atom in the metalloporphyrin was not coplanar with porphin ring, and zinc porphyrin has the most extent of its non-coplanar nature. The most stable complex in nine complexes was iron porphyrin. NBO analysis indicated that the interaction between the lone pair of electrons on the nitrogen atom and the unoccupied lone pair orbital of metal contributes significantly to the stability of the complexes. Through the conceptual DFT parameter and Fukui dual descriptor, the thermodynamic stability and reactivity of complexes were analyzed. The density difference function (DDF) analyzes were performed to explore the rearrangement of electronic density after the coordination interaction. NICS calculation indicated that metalloporphyrin aromaticity was reduced after the coordination interaction, and aromaticity of diazine tautomer was increased along direction vector of the coordination interaction force.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.40.1-40.1
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• 2013

We perform a set of N-body/SPH simulations of galaxy interactions between early- and late-type galaxies with the mass ratio of 2 to 1. We show that mass transfer during a fly by interaction (the closest approach distance ~50kpc) can cause the morphology transformation of an early-type galaxy to a late type. In our simulations, we vary the orbital parameters of the interactions and the cold gas fraction of the late-type galaxy to compare how the morphology transformation is affected by the amount of mass transfer and orbital angular momentum of cold gas accreted to the early type. We also include hot halo gas in the galaxy models and show the location of the tidal bridge can be influenced by the shock generated during the collision.