• Bulletin of the Korean Chemical Society
• /
• v.23 no.2
• /
• pp.337-345
• /
• 2002

The equilibrium structures for the ground and transition states of $C_7H_7^+$ isomers have been investigated using sophisticated ab initio quantum mechanical techniques with various basis sets. The structures of tropyrium and benzyl cations have been fully optimized at the DZP CCSD(T) levels of theory. And the structures of o-, m-and p-tolyl cations are optimized fully up to the DZ CCSD(T) levels of theory. The geometries for the transition states between three isomers of tolyl cations have been optimized up to DZP CISD level of theory. The SCF harmonic vibrational frequencies for tropylium, benzyl, and three isomers of tolyl cations are all real numbers, which confirm the potential minima and each unique imaginary vibrational frequencies for TS1 and TS2 confirm the true transition states. The relative energy of the benzyl cation with respect to the tropyrium cation is predicted to be 28.5 kJ/mol and is in good agreement with the previous theoretical predictions. The 0 K heats of formation, ${\Delta}H^{\circ}_{f0}$, have been predicted to be 890, 1095, 1101, and 1110 kJ/mol for tropylium, ortho-, meta-, and para-tolyl cations by taking the experimental value of 919 kJ/mol for the benzyl cation as the base level. The relative stability between tolyl cations is in the order of ortho

• Bulletin of the Korean Chemical Society
• /
• v.30 no.11
• /
• pp.2549-2554
• /
• 2009

The structures of 1,n-alkanedithiol (n = 2, 4, 6, 8, 10) self-assembled monolayers (SAMs) on a Au(111) substrate were investigated by electrochemical measurements and theoretical calculations. The results of the experimental techniques indicated that the dithiols, except n = 2, showed an upright molecular structure in the SAMs, in which alkanedithiols were bound to the Au surface via only one thiol functionality and the other one faced up to the air. The results also suggested that the formed dithiol SAMs were densely packed and highly oriented. Except ethanedithiol, which was thought to form a bilayer, the reductive desorption peak potentials of 1,n-alkanedithiol (n = 4, 6, 8, 10) SAMs were more negative than those of the corresponding monothiol ones in 0.1 M KOH solutions. This illustrates that the dithiol SAMs had higher stability than the corresponding monothiol ones. The major part of the high stability may be attributed to the van der Waals interaction among the sulfur atoms on top of the dithiol SAMs. The molecular modeling calculation showed that the structures of dithiol SAMs were similar to those of the corresponding monothiol SAMs and that all the dithiol SAMs, except ethanedithiol, were more stable than the corresponding monothiol SAMs. The calculated energy differences between dithiol and monothiol SAMs decreased with the increment of alkyl-chain length.

• Bulletin of the Korean Chemical Society
• /
• v.33 no.3
• /
• pp.971-974
• /
• 2012

The facilitated diffusion effect on protein-DNA binding is studied. A rigorous theoretical approach is presented to deal with the coupling between one-dimensional and three-dimensional diffusive motions. For a simplified model, the present approach can provide numerically exact results, which are confirmed by the lattice-based Monte Carlo simulations.

• Journal of the Korean Magnetic Resonance Society
• /
• v.10 no.1
• /
• pp.46-58
• /
• 2006

With a simple pulse sequence ($\pi/2$-{gradient, duration T}-acquisition) in solution NMR, detected signal has slowly grown up to percents of the equilibrium magnetization. The source of this unusual resurrection of dephased magnetization after a crushed gradient is cross-correlated effects of radiation damping and the distant dipolar field, which has been demonstrated by a numerical simulation and theoretical analysis.

• Journal of Photoscience
• /
• v.1 no.1
• /
• pp.75-82
• /
• 1994

General features of the fluorescence depolarization are briefly reviewed. Molecular rotations and electronic excitation transports are considered to account for the fluorescence depolarization. Various molecular systems studied by the fluorescence depolarization are described. The FiSrster theory which forms a basis for the energy transfer is revisited. Several theoretical treatments for the fluorescence depolarization in liquid and solid phases such as classical hydrodynamics, probability distribution function, Green's function formalism, molecular dynamics simulation and Monte Carlo methods are introduced.

• Journal of the Korean Chemical Society
• /
• v.57 no.2
• /
• pp.216-220
• /
• 2013

The hydroalumination of cyclopropane has been investigated using the B3LYP density functional method employing several split-valence basis sets. It is shown that the reaction proceeds via an intermediate weakly bound complex and a four-centered transition state. Calculations at higher levels of theory were also performed at the geometries optimized at the B3LYP level, but only slight changes in the barriers were observed. Structural parameters for the transition state are also reported.

• Proceedings of the Membrane Society of Korea Conference
• /
• 2003.07a
• /
• pp.11-16
• /
• 2003

A mathematical model describing the performance of a three phase catalytic membrane reactor for the partial oxidation of propane has been developed. The theoretical study pointed out that the recovery of products in the gas phase is strongly related to the membrane hydrophobicity.

• Bulletin of the Korean Chemical Society
• /
• v.4 no.1
• /
• pp.41-44
• /
• 1983

The chlorine addition and Diels-Alder cycloaddition of cyclopentadiene to 1, 4-benzoquinone-4-(O-methyloxime) have been studied MO theoretically. It has been shown that the reactions occur predominantly to the quinone ring double bond which is oriented anti to the nitrogen lone pair due to an n-${\sigma}^*$ interaction between the nitrogen lone pair, n, and the app. vicinal bond, causing the ${\pi}$ bond to be weakened and destabilized due to the less conjugation from reduced delocalization.

• Bulletin of the Korean Chemical Society
• /
• v.6 no.3
• /
• pp.132-135
• /
• 1985

Four types of the phase diagrams indicating the partial miscibilities in polymer-polymer or polymer-solvent systems have been explained in terms of the extended Flory-Huggins lattice theory. In this article, the term $kT_{\chi}$ in the theory is expressed as a function of temperature. Using such $a_{\chi}$-parameter, the simplest forms of geometrical conditions are derived for each type of the four partial miscibilities in polymer systems. The calculated partial miscibilities are in good agreement with the experiment.

• Bulletin of the Korean Chemical Society
• /
• v.7 no.5
• /
• pp.388-391
• /
• 1986

There are lipid phase theories and aqueous phase theories among the theories of anesthesia. For water clusters induced by anesthetizing molecules, the interaction energies are calculated using an empirical potential function and correlated with the anesthetizing partial pressures for mice. A good agreement was obtained with the theory that the water clusters around anesthetics play an important role on the anesthetic actions.