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Nucleophilic Substitution at a Carbonyl Carbon Atom(VI)
Lee, Hai-Whang,Lee, Ikchoon Korean Nuclear Society 1975 Nuclear Engineering and Technology Vol.7 No.4
Kinetic studies on the halide exchange reactions of substituted benzoyl chlorides have been carried out. The experimental result has been explained reasonably in terms of HSAB principle and EH-Theory, and addition elimination mechanism has been proposed for this type of reaction.
An MO Theoretical Studies on Conformations of Methyl and Ethyl Chanoacetates
Lee, Ikchoon,Kim, Jik-Tae,Kim, Ui-Rak Korean Nuclear Society 1974 Nuclear Engineering and Technology Vol.6 No.3
The extended Huckel molecular orbital calculations have been carried out on rotamers of methyl and ethyl cyanoacetates. Results show that cis orientation of C≡N group is favored while for $CH_3$group trans orientation is favored. The major part of the stabilization energies can be accounted for by the electrostatic energies between the atoms involved.
LEE, IKCHOON,RHYU, KEUN WOO,LEE, HAI WHANG,SHIM, CHANG SUB,OH, HYUCK KEUN 全北大學校 基礎科學硏究所 1991 基礎科學 Vol.14 No.2
Kinetic studies on the reactions of methy1 (MBS) and ethyl benzenesulphonates (EBS) with N, N-dimethylanilines (DMA) in methanol and acetonitrile are reported. The cross interaction constants ρ_XZ and β_XZ, between the substituents in the nucleophile (X) and the leaving group (Z) indicated that the transition states (TS) are looser than those for the reactions with anilines, but the relative tightness between the two substrates was the same; the TS was tighter for EBS despite the increase in steric effect leading to looser TSs for MBS and EBS alike. The TS variation between two different reaction series expected from the simple Hammett and Bronsted coefficients, ρ_X, ρ_Z, β_X and β_Z, was incompatible with that predicted by the cross interaction constants, demonstrating again the unreliability of the simple parameters.
Lone Pairs in the 1,3-Sigmatropic Group Rearrangements
Lee, Ikchoon,Cho, Jeoung Kl,Lee, Bon-Su,Oh, Hyuck Keun 全北大學校 基礎科學硏究所 1991 基礎科學 Vol.14 No.1
Semiempirical computations using the AM1 and MNDO methods were carried out in order to elucidate allowed mechanisms for 1,3-group(X) rearrangement processes with X = BH_2, CH_3, CN, F, NH_2, OH, Cl and SH. The reactivity of the group migration was largely controlled by the steric effect in the 4-membered ring transition state, an antarafacial process having a greater energy barrier due to a greater steric repulsion. For the groups with lone pair electrons, the participation of the lone pair orbital is found to ease the steric effect by enabling the FMO interation with highly polarizable, high lying, lone pair electrons at relatively distant range; the involvement of lone pairs in the transition state causes an alteration of the symmetry selection rule to that of a 6-electron system with an allowed 1,3-suprafacial migration in contrast to an allowed 1,3-antarafacial migration for a 4-electron system. Various stereoelectronic aspects were analysed in some detail.
Ikchoon Lee,Chul Hyun Kang,Pyoung Sam Park,Hai Whang Lee Korean Chemical Society 1991 Bulletin of the Korean Chemical Society Vol.12 No.3
Kinetic studies of the reactions of benzyl benzenesulfonates with benzylamines in methanol and acetonitrile have been carried out. The reaction was found to proceed by a dissociative $S_N2$ in MeCN but by an associative $S_N2$ mechanism in MeOH. The transition state was rather loose in MeCN whereas it was tight in MeOH, in contrast to a tighter TS in MeCN for the corresponding reactions with aniline. The reaction of benzylamine in MeOH was characteristic of the highly solvated nucleophile, benzylamine, compared to the normal reaction in MeCN.
MO Theoretical Studies on the Benzylic and Resonance Shunt Effects
Ikchoon Lee,Jeong Ki Cho,Chang Kon Kim Korean Chemical Society 1991 Bulletin of the Korean Chemical Society Vol.12 No.2
The reactions of aniline with benzyl and phenacyl compounds are studied by the AM1 method. Two types of modeling were adopted: Cation-neutral, in which a proton is attached to the leaving group F and anion-neutral model, in which aniline was replaced by phenoxide with Cl as the leaving group. The cation-neutral model represented the reactvery well, reproducing the various solution-phase experimental results. In the benzyl system, the ${\pi}$-electrons of the two rings (X-ring in the nucleophile and Y-ring in the substrate) interact conjugatively in the transition state (TS) resulting in a bond contraction of the $C_{\alpha}-C_{Y1}$ bond (benzylic effect), whereas in the phenacyl system the ${\pi}$ electrons of the X-ring delocalizes more efficiently into the carbonyl group than into the Y-ring (resonance shunt effect) with a bond contraction of the $C_{\alpha}-C_{\beta}$ bond. The bond contraction in the benzylic effect was substantially greater than that in the resonance shunt effect. The TS was rather loose for benzyl while it was tighter for phenacyl system. Various bond length changes with substituents in the TS were, however, found to be irregular.
Kinetic Studies on the Halide Exchange Reactions of Some Substituted Benzyl Chlorides
Lee, Ikchoon,Lee, Bon-Su,Yie, Jae-Eui Korean Nuclear Society 1971 Nuclear Engineering and Technology Vol.3 No.4
Kinetic studies on the halide exchange reactions of some substituted benzyl chlorides have been carried out using radioisotope tracer halide ions. Results are consistent with our previous conclusion that the rates of halide exchange reactions in acetone with arylmethy halides are dictated by the porarizabilities of both substrate and nucleophile.
Lee, Ikchoon,Hang, Seong Wan,Park, Jin Ha 全北大學校 基礎科學硏究所 1991 基礎科學 Vol.14 No.1
The transition state(TS) structure for the reactions of phenacyl benzenesulfonates with N,N-dimethylanilines(DMA) is investigated using various selectivity parameters, especially with crosss-constants, Ρ_ij, β_ij and λ_ij. The trends in reactivity were similar to aniline series but the TS was found to be somewhat looser than that for aniline series. It was found that the RSP and BEP principle hold within the DMA series but are violated between two different rcaction series with DMA and aniline.