• Journal of the Korean Chemical Society
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• v.32 no.3
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• pp.163-170
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• 1988

The MNDO calculations were performed on the various rotamers of N-methyl formamide, N,N-dimethyl formamide, N-methyl acetamide, and N,N-dimethylacetamide in order to investigate the contribution of the one-electron and the steric effect on their rotational barriers about the C-N bond. Results show that while the conformational stabilities of formamides depend mainly on the one-electron factor, those of acetamides depend mainly on the steric factor. According to results obtained by calculations on the rotational barriers about C-N bond, for N-monosubstituted amides the steric effect is larger in the rotational ground state than in the transition state and for N,N-disubstituted amides the steric effect is larger in the rotational transition state.

• Journal of the Korean Applied Science and Technology
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• v.36 no.1
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• pp.174-188
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• 2019

The present study was carried out to investigate the emulsifying properties of heat-treated octenyl succinic anhydride(OSA) starch and the interfacial structure at oil droplet surface in emulsions stabilized by heat-treated OSA starch. First, the aqueous suspensions of OSA starch were heated at $80^{\circ}C$ for 30 min. Oil-in-water emulsions were then prepared with the heat-treated OSA starch suspension as sole emulsifier and their physicochemical properties such as fat globule size, surface load, zeta-potential, dispersion stability, confocal laser scanning microscopic image(CLSM) were determined. It was found that fat globule size decreased as the concentration of OSA starch in emulsions increased, showing a lower limit value ($d_{32}:0.31{\mu}m$) at ${\geq}0.2wt%$. Surface load increased steadily with increasing OSA starch concentration in emulsions, possibly forming multiple layers. In addition, fat globule sizes were also influenced by pH: they were increased in acidic conditions and these results were interpreted in view of the change in zeta potentials. The dispersion stability by Turbiscan showed that it was more unstable in emulsions at acidic condition. Heat-treated OSA starch found to adsorb at the oil droplet surface as some forms of membrane (not starch granules), which might be indicative of stabilizing mechanism of OSA starch emulsions to be steric forces.

• Journal of the Korean Chemical Society
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• v.18 no.4
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• pp.223-238
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• 1974

CNDO/2 MO theoretical studies and kinetic studies of halide exchange reactions for alkylchloroformates have been carried out in order to investigate structure-reactivity relationship of alkylchloroformates. From the result of energetics, it was concluded that the most stable configuration of alkylchloroformate is that in which alkyl group and chlorine are trans to each other, and that the hindered rotation about the bond between the carbonyl carbon and alkoxy-oxygen bond is attributed to the ${\pi}-$electron delocalization. It has been found that the large charge separation is due to -M effect of carbonyl and alkoxy oxygens and-I effect of chlorine. The order of rates in solvents studied was $(CH_3)_2 > CO > CH_3CN{\gg}MeOH.$$I^->Br^->Cl^-$ in protic solvent, and of Cl^->Br^- >I^-$ in dipolar aprotic solvents. Alkyl group contribution has the decreasing order of $CH_3-> C_2H-{\gg}i-C_3H_7-.$ The solvent effect has been interpreted on the basis of initial and final state contribution. A transition state model has been suggested, and it has been proposed that the most favorable mechanism is the addition-elimination. From the results of activation parameters and electronic properties, an energy profile has been proposed. Structural factors determining reactivities of alkylchloroformates have been shown to be charge, energy level of ${\alpha}^*LUMO$ to C-Cl bond and ${\alpha}^{\ast} $antibonding strength with respect to C-Cl bond in this MO. Charge and polarizability of nucleophile, and the interaction of these effects with solvent structures are also found to be important.