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Orbital Interactions in$ BeC_{2}H_{2}\;and\;LiC_{2}H_{2}$ Complexes
Ikchoon Lee,Jae Young Choi Korean Chemical Society 1993 Bulletin of the Korean Chemical Society Vol.14 No.1
Ab initio calculations are carried out at the 6-311G$^{**}$ level for the $C_{2v}$ interactions of Be and Li atoms with acetylene molecule. The main contribution to the deep minima on the $^3B_2\;BeC_2H_2\;and\;^2B_2 LiC_2H_2$ potential energy curves is the b_2\;(2p(3b_2)-l{\pi}_g^*(4b_2))$ interaction, the $a_1\;(2s(6a_1)-I{\pi}_u(5a_1))$ interaction playing a relatively minor role. The exo deflection of the C-H bonds is basically favored, as in the $b_2$ interaction, due to steric crowding between the metal and H atoms, but the strong in-phase orbital interaction, or mixing, of the $a_1$ symmetry hydrogen orbital with the $5a'_1,\;6a'_1,\;and\;7a'_1$ orbitals can cause a small endo deflection in the repulsive complexes. The Be complex is more stable than the Li complex due to the double occupancy of the 2s orbital in Be. The stability and structure of the $MC_2H_2$ complexes are in general determined by the occupancy of the singly occupied frontier orbitals.
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.
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.
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.
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.
Theoretical Studies of 1,5-Sigmatropic Rearrangements Involving Group Transfer$^1$
IkChoon Lee,Bon Su Lee,Nam Doo Kim,Chang Kon Kim Korean Chemical Society 1992 Bulletin of the Korean Chemical Society Vol.13 No.5
The 1,5-sigmatropic rearrangements involving group (X) migration in ${\omega}$(X)-substituted 1,3-pentadiene, $C^1H_2=C^2H-C^3H=C^4H-C^5H_2-X$, where X = H, $CH_3$, $BH_2$, $NH_2$, OH or F, are investigated MO theoretically using the AM1 method. For the migrating groups without lone pair electrons, X = H, $CH_3$, or $BH_2$, the suprafacial pathway is favored, whereas for the migrating groups with lone pair electrons participating in the TS, $X=NH_2$, OH, or F, the antarafacial pathway is favored electronically. However excessive steric inhibition in the antarafacial TS for $X=NH_2$ leads to subjacent orbital controlled suprafacial process. The antarafacial shift of F is relatively disfavored compared to that of OH due to smaller orbital overlap and larger interfrontier energy gap in the TS.
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.