• Bulletin of the Korean Chemical Society
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• v.21 no.5
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• pp.465-470
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• 2000

The conformations and energies of p-tert-butylcalix[4] crown-6-ether (1) and its alkyl ammonium complexes have been simulated by AM1 semi-empirical quantum mechanics and molecular mechanics calculations using a variety of forcefields (MM2, MM+, CVFF). We performed molecular dynamics calculations to simulate the behavior of these coplexes primartily focusing on the three representative conformations (cone, partial cone, 1,3-alternate) of host molecule 1. When we performed AM1 semi-empirical and molecular mechanics calculations, the one conformation was generally found to be most stable for all the employed calculation methods. The primary binding site of host 1 for the recognition of alkyl ammonium guests was confirmed to be the central part of the crown moiety. The complexation enthalpy calculations revealed that the alkyl amonium cations having smaller and linear alkyl group showed the better complexation efficiencies when combined with p-tert-butylcalix[4]crown-6-ether, that is in satisfactory agreement with the experimental results.

• Journal of the Korean Applied Science and Technology
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• v.19 no.3
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• pp.161-166
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• 2002

The alkaline hydrolysis of alkyl alkylphosphinate and alkyl phenylphosphinates have been studied at room temperature. The hydrolysis proceeded as an one-stage reaction($S_{N}$ 2) and involved a nucleophilic attack of the hydroxyl ion on the phosphorus atom. And the length of the alkoxy group in the phosphinate esters affected on hydrolysis. Therefore, the alkaline hydrolysis may be used as a method to decompose the chemical agents.

• Bulletin of the Korean Chemical Society
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• v.23 no.6
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• pp.891-896
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• 2002

The structures and energies of p-tert-butylcalix[4]crown-6-ether(1) in various conformers and their alkyl ammonium complexes have been calculated by ab initio HF/6-31G quantum mechanics method. We have tried to obtain the relative affinity of partial-cone and 1,3-alternate conformers of 1 for alkyl ammonium guests by comparison with its cone-shaped analogue. We have also calculated the relative complexation efficiency of these host-guest complexes focusing on the binding sites of $crown-\sigma-enther$ moiety or benzene-rings pocket of the host molecule 1. These calculations revealed that the crown moiey has better complexation efficiency than upper rim part of calyx[4]arene that is in similar trend to the cone-shaped complexes.

• Bulletin of the Korean Chemical Society
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• v.17 no.3
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• pp.269-273
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• 1996

Alkyl halides were reduced to the corresponding alkanes by the homonuclear bridging hydride, (μ-H)[(η5-MeCp)Mn(CO)2]2-PPN+ in THF at the elevated temperatures (40-60 ℃) under the pseudo first order reaction conditions where excess of alkyl halide was employed under nitrogen atmosphere. The reaction is of overall second order; first order with respect to [bridging hydride] and first order with respect to [alkyl halide] with the activation parameters, ΔH≠=28.93 kcal/mol and ΔS≠=17.95 e.u. The kinetic data, the ESR evidence and the reaction with cyclopropyl canbinyl bromide ensure that two possible reaction pathways are operable in this reaction: (1) concerted mechanism, and (2) single electron transfer pathway are in competition leading to the same product, the corresponding alkane.

• Bulletin of the Korean Chemical Society
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• v.13 no.3
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• pp.280-285
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• 1992

Enantiomeric separation of free amino acids has been achieved by a reversed phase liquid chromatography with addition of a Cu(Ⅱ) complex of N-alkyl-L-proline (alkyl: propyl, pentyl or octyl) to the mobile phase. The amino acids eluted were detected by a postcolumn OPA system. N-alkyl-L-proline was prepared and used as a chiral ligand of Cu(Ⅱ) chelate for the enantiomeric separation. The concentration of the Cu(Ⅱ) chelate, the organic modifier and pH affect the enantiomeric separation of free amino acids. The retention behaviour, varied with change in pH and the concentration of the Cu(Ⅱ) chelate, was different compared with those of the derivatized amino acids. The elution orders between D- and L-forms were consistent except histidine showing that L-forms elute earlier than D-forms. The retention mechanism for the enantiomeric separation can be illustrated by the stereospecificity of the ligand exchange reaction and the hydrophobic interaction between the substituent of amino acids and reversed phase, $C_18$.

• Journal of the Korean Chemical Society
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• v.45 no.5
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• pp.454-460
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• 2001

The reaction of 3-methoxycarbonylmethylene-2-oxo-1,2,3,4-tetrahydroquinoxaline(7) with hydrazine hydrate gave 3-hydrazinocarbonylmethylene-2-oxo-1,2,3,4-tetrahydroquinoxaline(8). The reaction of compound 8 with alkyl (ethoxymethylene)cyanoacetates gave the [(quinoxalin-2-ylidene)ethanoyl]-1H-pyra-zoles(9). The reaction of compound 9b with N-alkylanilines provided the N-alkyl-(quinoxalin-2-ylidene)-N-phenylethanamides(10). Compounds 9 and 10 showed the tautomerism between the enamine and methylene imine forms in solution. The tautomer ratios were determined by the $^1H$ NMR.

• Bulletin of the Korean Chemical Society
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• v.15 no.6
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• pp.460-465
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• 1994

New silicon-monosubstituted (${\eta}^4$-2,3,4,5-tetraphenyl-l-silacyclopentadiene)transi tion metal complexes are described. (7-Alkyl-7-silanorbornadienyl)MLn(Alkyl=Methyl: MLn=CpRu$(CO)_2$: Alkyl=Methyl: MLn=CpNi(CO): Alkyl=Ethyl: MLn=CpNi(CO)) complexes were prepared from the corresponding silole-transition metal complexes with dimethylacetylenedicarboxylate. Cycloaddition products were obtained with 2,3-dimethyl-1,3-butadiene, 2,3-butanedione, and 1,4-benzoquinone through the ruthenium-substituted silylene. We have determined the crystal structure of (1-methyl-2,3,4,5-tetraphenyl-l-silacyclopentadien yl)cyclopentadienyldicarbonylruthenium by using graphite monochromated Mo-Ka radiation. The compound was crystallized in the monoclinic space group $P2_{1/c}$ with a = 9.838(l), b = 15.972(3), c = 18.327(3) ${\AA}$, and ${\beta}= 94.28(l)^{circ}$. The ruthenium moiety CpRu$(CO)_2$ on silicon is in an axial position.

• Bulletin of the Korean Chemical Society
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• v.24 no.7
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• pp.895-896
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• 2003

• Bulletin of the Korean Chemical Society
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• v.34 no.1
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• pp.174-178
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• 2013

A highly reliable dealkylation protocol of alkyl aryl ethers, whose alkyl groups are longer than methyl group, has been developed. We report that various ethyl, n-propyl, and benzyl aryl ethers are successfully cleaved using an ionic liquid, 1-n-butyl-3-methylimidazolium bromide, [bmim][Br], under microwave irradiation. Despite many characteristics such as lower cost and less toxicity of the alkylating agents, and greater hydrophobicity of the products, longer alkyl ethers have been significantly less exploited than methyl ethers, probably due to more difficulty in the deprotection step. Since it has the same advantages as the demethylation method developed by this group including mild conditions, short reaction time, and small use of the ionic liquids, the dealkylation protocol can greatly encourage the broader use of longer alkyl groups in the protection of phenolic groups. As with our previous study of demethylation using [bmim][Br], the microwave irradiation is crucial for the deprotection of longer alkyl aryl ethers. Unlike the conventional heating, which causes either low conversion or decomposition, the microwave irradiation seems to more effectively provide energy to cleave the ether bonds and therefore suppresses the undesired reactions.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.12 no.1
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• pp.69-74
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• 1999

We have investigated that the high pretilt angle of the NLC, 4-n-pentyl-4-cyanobiphenyl (5CB), was observed on rubbed polythiophene (PTP) surfaces with alkyl chains with more than 10 carbon atoms; it is attributed to the surface-excluded volume effect by the alkyl chain lengths between the LCs and the PTP surfaces. Next, we investigated that the odd-even effect of the polar anchoring strength in 5CB on rubbed PTP surfaces with alkyl chain lengths has been successfully evaluated. The anchoring strength of 5CB for rubbed PTP surfaces with odd-number is weak compared with even-number up to the 6 carbon atoms in the alkyl chain; however, odd-number is strong compared with even-number above 7 carbon atoms. The weak anchoring strength of 5CB is approximately $1\times10^{-3} (J/m^2$) on rubbed PTP surface with 7 carbon atoms; it is relatively strong anchoring strength. Consequently, we conclude that the odd-even effects of the polar anchoring strength in NLCs are strongly related to the characteristics of the polymer and observed clearly for short alkyl chain lengths.