• 대한화학회지
• /
• 제18권3호
• /
• pp.171-174
• /
• 1974

Sulfonyl chloride $ RSO_2Cl,\;R=C6H_5-,\;CH3-,\;OCH3-$ 및 $(CH_3)_2N-$에 대하여 EHT계산을 하였으며 바닥상태의 전자구조 특성과 $S_N$반응성을 논의하였다. 특히 $R=OCH_3$의 경우 Buncel이 제안한 Cl에서의 치환가능성을 검토하였다.

• 대한화학회지
• /
• 제6권2호
• /
• pp.148-154
• /
• 1962

The reactions between organic halides$(CCl_4,\;C_6H_5Br,\;C_6H_5Cl,\;C_6H_5I)$ and amines $(C_6H_5NH_2,\;R_2NH,\;R_3N,\;(CH_2)_5NH,\;pyridine)$ were studied under mixed u.v. irradiation. The modes of reactions were examined by means of gas chromatography and product-reactant ratio determination. The reaction of $CCl_4$ with amines give chloroform and hexachloroethanes, and the reaction of aromatic halides with amines gave biphenyl and benzene. In each series of reaction there obtained mainly corresponding amine hydrohalides, but no amination products. The reactivity was in the order of the basicity of amines and of the reactivity of organic hahides, except in the case of cyclic tertiary amine. The result was interpreted as a non-chain photodecomposition process. A competitive proton abstraction reaction path via the formation of a change transfer complex was proposed as the reaction mechanism.

• Journal of Pharmaceutical Investigation
• /
• 제6권2호
• /
• pp.95-100
• /
• 1976

A study on the effect of the pH of precipitation on the acid consuming capacity, aging stability, physical and chemical properties of hydrous aluminum oxide prepared by the reaction of aluminum chloride and ammonium hydroxide solution was carried out by means of X-ray diffraction, IR spectra and differential thermal analysis. The results from these experiments are as follows: 1. Hydrous aluminum oxide precipitated at lower pH showed better acid consuming capacity, higher stability and more anion contained in the structure than that prepared at higher pH. 2. The hydrous aluminum oxide prepared at lower pH is amorphous and that prepared at higher pH is crystalline hydrated hydrous aluminum oxide, i.e., Bayerite and these results are conformed to Rhee's hypothesis. 3. The rate of loss of reactivity and the end-point reactivity are related to the pH of precipitation.

• Bulletin of the Korean Chemical Society
• /
• 제24권7호
• /
• pp.925-930
• /
• 2003

Kinetic studies of the reaction of Z-aryl cyclopropanecarboxylates with X-pyridines in acetonitrile at 55.0 ℃ have been carried out. The reaction proceeds by a stepwise mechanism in which the rate-determining step is the breakdown of the zwitterionic tetrahedral intermediate, $T^{\pm}$. These mechanistic conclusions are drawn base on (i) the large magnitude of ρx and ρz, (ii) the positive sign of ρxz and the larger magnitude of ρxz than normal $S_N2$ processes, (iii) a small positive enthalpy of activation, Δ$H^≠$, and a large negative, Δ$S^≠$, and lastly (iv) adherence to the reactivity-selectivity principle (RSP) in all cases.

• Bulletin of the Korean Chemical Society
• /
• 제29권9호
• /
• pp.1732-1736
• /
• 2008

The endogenous dipeptides, carnosine and related compounds, are the naturally occurring dipeptides with multiple neuroprotective properties. We have examined the protective effects of carnosine, homocarnosine and anserine on the aggregation of neurofilament-L (NF-L) induced by neurotoxin, acrolein. When NF-L was incubated with acrolein in the presence of carnosine, homocarnosine or anserine, protein aggregation was inhibited in a concentration-dependent manner. These compounds inhibited the formation of protein carbonyl compounds and dityrosine in acrolein-mediated NF-L aggregates. The aggregates of NF-L displayed thioflavin T reactivity, reminiscent of amyloid. This thioflavin T reactivity was inhibited by carnosine and related compounds. This effect was associated with decreased formation of oxidatively modified proteins. Our results suggested that carnosine and related compounds might have protective effects to brain proteins under pathophysiological conditions leading to degenerative damage such as neurodegenerative disorders.

• 대한화학회지
• /
• 제20권2호
• /
• pp.136-140
• /
• 1976

오르토-터페닐계 화합물들의 광화학적 탈수소 고리화 반응을 섭동분자궤도론적으로 다루었으며 일차 들뜬 상태의 가동결합차수가 반응성의 좋은 지표가 될 수 있음을 밝혔다. 이 해석은 Woodward-Hoffman의 궤도함수 대칭성 보존법칙에도 부합된다.

• Bulletin of the Korean Chemical Society
• /
• 제1권3호
• /
• pp.98-101
• /
• 1980

For the first time we have synthesized thiabenzene radical by the reaction of thiopyrylium cation with alkali metals. As might be expected for a free radical, ESR-spectrum of 2,4,6-triphenylthiabenzene radical shows the single signal with g-value of 2.0045. The proton signal of 2,4,6-triphenylthiabenzene radical in nmr spectrum shifts to the higher field than that of 2,4,6-triphenylthiopyrylium cation by ca. 0.5 ppm. From the UV-spectrum of thiabenzene radical the presence of 6${\pi}$ non-benzenoid aromatic system was observed as in the case of thiopyrylium cation. The reactivity of alkali metals with thiopyrylium cation increases in the order of decreasing ionization energy, Li

• Bulletin of the Korean Chemical Society
• /
• 제5권3호
• /
• pp.126-129
• /
• 1984

The reaction of aryl halides with phenoxides and alkoxides were investigated under phase transfer catalytic conditions. 2,4-Dinitro- and 4-nitrohalobenzenes reacted readily with phenoxides in NaOH(aq)-benzene in the presence of Bu4N+Br, affording the products quantitatively. Although the aryl halides did not react with alkoxides under the same condition, the reactions were completed within 2 hours at room temperature when conducted under solid-liquid phase transfenr catalytic condition. The reactivity of aryl halides was in the order, Ar = 2,4-dinitrophenyl > 4-nitrophenyl, and X = F > Cl, consistent with the SNAr mechanism. The reactivity of oxyanions increased with the change of reaction condition from liquid-liquid to solid-liquid phase transfer catalysis. The results were explained with the concentration and the degree of hydration of the anion in benzene.

• Bulletin of the Korean Chemical Society
• /
• 제17권9호
• /
• pp.840-845
• /
• 1996

Rate constants have been measured spectrophotometrically for the reactions of p-and m-nitrophenyl 2-thiophenecarboxylate (5a and 5b, respectively) with alkali metal ethoxides (EtO-M+) in absolute ethanol at 25.0±0.1 ℃. The reactivity of EtO-M+ exhibits dependence on the size of alkali metal ions, i.e. the reactivity of EtO-M+ toward 5a decreases in the order EtO-K+ ≥ EtO-Na+ > EtO-Li+ > EtO-, while the one toward 5b does in the order EtO-Na+ ≥ EtO-K+ > EtO-Li+ > EtO-. This result indicates that ion paired EtO-M+ is more reactive than dissociated EtO-, and alkali metal ions form complexes with the substrate more strongly at the transition state than at the ground state. The catalytic effect shown by alkali metal ions appears to be less significant in the reaction of 5 than in the corresponding reaction of 4, indicating that complexation of alkali metal ions with 5 is not as strong as the one with 4.

• Bulletin of the Korean Chemical Society
• /
• 제18권8호
• /
• pp.865-868
• /
• 1997

Second-order rate constants have been measured spectrophotometrically for the reactions of p-nitrophenyl phenylacetate (1) and benzoate (2) with a series of alicyclic amines in H2O containing 20 mole % DMSO at 25.0 ℃. 1 appears to be more reactive than 2 toward all the amines studied, although phenylacetic acid is a weaker acid than benzoic acid. The higher reactivity of 1 can be attributed to resonance and/or steric effect, since the ground state of 2 can be stabilized by resonance and 1 would experience less steric hindrance due to the presence of CH2 group between phenyl and C=O group. The reactivity of the amines increases with increasing their basicity. The Bronsted-type plots for aminolysis of 1 and 2 show good linearity with βnuc values of 0.81 and 0.85, respectively, indicating that the TS structures of the aminolyses of 1 and 2 are similar. Besides, the linear Bronsted plots obtained in the present system clearly suggest that there is no mechanism change for the given series of the amines and the reactions of 1 and 2 proceed in a same mechanism.