• Bulletin of the Korean Chemical Society
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• 제33권8호
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• pp.2707-2710
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• 2012

The nucleophilic substitution reactions of O-ethyl phenyl phosphonochloridothioate with substituted anilines ($XC_6H_4NH_2$) and deuterated anilines ($XC_6H_4ND_2$) are kinetically investigated in acetonitrile at $55.0^{\circ}C$. The deuterium kinetic isotope effects (DKIEs) invariably increase from a secondary inverse DKIE ($k_H/k_D$ = 0.93) to a primary normal DKIE ($k_H/k_D$ = 1.28) as the substituent of nucleophile (X) changes from electron-donating to electron-withdrawing. These can be rationalized by the gradual transition state (TS) variation from a backside to frontside attack. A concerted $S_N2$ mechanism is proposed. A trigonal bipyramidal TS is proposed for a backside attack while a hydrogen-bonded, four-center-type TS is proposed for a frontside attack.

• Bulletin of the Korean Chemical Society
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• 제33권3호
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• pp.775-778
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• 2012

The potential energy surfaces of ammonia molecule adsorptions on the symmetrically chlorinated Si(100)-$2{\times}1$ surface were explored with SIMOMM:MP2/6-31G(d). It was found that the initial nucleophilic attack by ammonia nitrogen to the surface Si forms a $S_N2$ type transition state, which eventually leads to an HCl molecular desorption. The second ammonia molecule adsorption requires much less reaction barrier, which can be rationalized by the surface cooperative effect. In general, it was shown that the surface Si-Cl bonds can be easily subjected to the substitution reactions by ammonia molecules yielding symmetric surface Si-$NH_2$ bonds, which can be a good initial template for subsequent surface chemical modifications. The ammonia adsorptions are in general more facile than the corresponding water adsorption, since ammonia is better nucleophile.

• Bulletin of the Korean Chemical Society
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• 제33권3호
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• pp.843-847
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• 2012

The nucleophilic substitution reactions of dibutyl chlorothiophosphate (4S) with substituted anilines ($XC_6H_4NH_2$) and deuterated anilines ($XC_6H_4ND_2$) are investigated kinetically in acetonitrile at $55.0^{\circ}C$. The obtained deuterium kinetic isotope effects (DKIEs;$k_H/k_D$) are primary normal ($k_H/k_D$ = 1.10-1.35). A concerted mechanism involving predominant frontside nucleophilic attack is proposed on the basis of the primary normal DKIEs and selectivity parameters. Hydrogen bonded, four-center-type transition state is proposed. The steric effects of the two ligands on the anilinolysis rates of the chlorothiophosphates are discussed. The anilinolyses of P=S systems are compared with those of their P=O counterparts on the basis of the reactivities, thio effects, selectivity parameters, and DKIEs.

• 대한화학회지
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• 제24권5호
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• pp.347-355
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• 1980

${\alpha}$- 및 ${\beta}$-염화나프탈렌카르보닐의 가메탄올 분해반응속도를 메탄올-아세톤, 메탄올-아세토니트릴 혼합용매 속에서 측정하였다. 각 혼합용매마다 공통적으로 ${\alpha}$-염화나프탈렌카르보닐이 ${\beta}$-염화나프탈렌카르보닐보다 반응속도 상수가 크게 관측되었다. 이것은 Dewar수 Nr과 Streitwieser의 ${\sigma}^+$값과도 일치하였다. 카르보닐탄소가 천이상태에서 $sp^3$로 바뀌어 인접수소에 의한 입체장애가 없어지는 것을 알 수 있었다.

• 한국세라믹학회지
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• 제25권4호
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• pp.321-328
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• 1988

The sintering phenomena, electrical resistivity, dielectric and piezoelectric properties of lead titanate ceramics modified by the partial substitution of La for Pb and Mn for Ti, (Pb1-1.5xLax)(Ti1-yMny)O3 ceramics, have been investigated. In (Pb1-1.5xLax)(Ti1-yMny)O3 system, with increasing lanthanum content, the realtive bulk density increased, but the Curie point and tetragonality (c/a) decreased. The tetragonal-to-cubic phase transition boundary existed in the range of 0.20

• Progress in Superconductivity
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• 제10권2호
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• pp.128-132
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• 2009

Polycrystalline samples of $(Ru_{0.8}Nb_{0.2})Sr_2(Gd_{1.5-x}Nd_xCe_{0.5})Cu_2O_z$($ 0{\leq}x{\leq}1.25$) have been synthesized by a solid-state reaction route. The X-ray diffraction data revealed that the Nd solubility limit can be placed between x=0.5 and x=0.75. The superconducting transition temperature decreased with increasing Nd content, confirming that Nd entered the lattice. Room-temperature thermoelectric power measurements showed that all the samples are in the underdoped state and the partial substitution of Nd for Gd resulted in a decrease in the carrier density on the superconducting layers.

• Bulletin of the Korean Chemical Society
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• 제35권3호
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• pp.815-820
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• 2014

We applied the two-color resonant two-photon ionization and mass-analyzed threshold ionization techniques to record the vibronic and cation spectra of 2,4-difluorophenol. As supported by our theoretical calculations, only the cis form of 2,4-difluorophenol involves in the two-photon photoexcitation and pulsed field ionization processes. The band origin of the $S_1{\leftarrow}S_0$ electronic transition of cis-2,4-difluorophenol appears at 35 647 ${\pm}2cm^{-1}$ and the adiabatic ionization energy is determined to be 70 $030{\pm}5cm^{-1}$, respectively. Most of the observed active vibrations in the electronically excited $S_1$ and cationic ground $D_0$ states mainly involve in-plane ring deformation vibrations. Comparing these data of cis-2,4-difluorophenol with those of phenol, cis-2-fluorophenol, and 4-fluorophenol, we found that there is an additivity rule associated with the energy shift resulting from the additional fluorine substitution.

• 한국세라믹학회지
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• 제18권2호
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• pp.75-78
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• 1981

The electrical conductivity of $(M_2O_3)_x (BaTiO_3)_{1-x}$ has been measured over the temperature range of 30 to 27$0^{\circ}C$. The substitution of rare earth oxide such as $La_2O_3$, $Nd_2O_3$, or $Dy_2O_3$ can be represented by $M_2O_3$. The additional mole fraction of the rare earth oxide is ranged over 0.0015 to 0.0030. The electrical conductivity exhibits an anomalous decrease near the tetragonal to cubic transition about 12$0^{\circ}C$. The decrease in the electrical conductivity is observed at the higher impurity concentrations owing to space charge layer. The increase in the electrical conductivity is observed as the impurity ion is varied from $La^{+3}$$Nd^{+3}$ to $Dy^{+3}$, due to overlap of 4f electrons of the inner shell.

• 대한화학회지
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• 제25권3호
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• pp.145-151
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• 1981

기체상에서의 이분자 친핵성치환반응에 대한, 고유한 반응성에 대하여 CNDO/2 방법의 분자궤도론적으로 논의 하였다. 친핵체 및 이탈기별로 반응물, 천이상태, 그리고 생성물에 대해 geometry optimization을 하고 구조와 형태를 고찰하였다. CNDO/2수준에서도 정성적인 논의가 가능하였으며 반응성은 친핵체의 염기도와 이로부터 유발된 분극력에 의해 지배되었다

• Bulletin of the Korean Chemical Society
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• 제32권12호
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• pp.4403-4407
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• 2011

The nucleophilic substitution reactions of dipropyl chlorothiophosphate (3) with substituted anilines ($XC_6H_4NH_2$) and deuterated anilines ($XC_6H_4ND_2$) are investigated kinetically in acetonitrile at $55.0^{\circ}C$. The obtained deuterium kinetic isotope effects (DKIEs; $k_H/k_D$) are primary normal ($k_H/k_D$ = 1.11-1.35). A concerted mechanism involving predominant frontside nucleophilic attack is proposed on the basis of the primary normal DKIEs and selectivity parameters. Hydrogen bonded, four-center-type transition state is proposed. The steric effects of the two ligands on the anilinolysis rates of various substrates are discussed.