• Bulletin of the Korean Chemical Society
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• 제27권5호
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• pp.687-693
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• 2006

Chromium(III) complexes, cis-[Cr([14]-decane)$(HOC _6H _4COO) _2$]$ClO _4$ I and cis-[Cr([14]-decane)(OH) $(OC _6H _4NO _2)$]$ClO _4{\cdot}H _2O$ II ([14]-decane = rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-teraazacyclotetradecane) are synthesized and structurally characterized by a combination of elemental analysis, conductivity, IR and VIS spectroscopy, and X-ray crystallography. The complexes crystallizes in the monoclinic space groups, $C2 _1$/a in I and $P2 _1$/n in II. Analysis of the crystal structure of complex I reveals that central chromium(III) ion has a distorted octahedral coordination environment and two hydrogensalicylato ligands are unidentate to the chromium(III) ion via the carboxyl groups in the cis-position. For monomeric complex I the hydrogensalicylato coordination geometry is as follows: Cr-O(average) = 1.984(3) $\AA$;Cr-N range = 2.105(3)-2.141(4) $\AA$;C(24)-O(4) = 1.286(5) $\AA$;N(2)-Cr-N(4) (equatorial position) = 96.97(15)${^{\circ}}$; N(1)-Cr-N(3) (axial position) = 168.27(15)${^{\circ}}$; O(1)-Cr-O(4) = 85.70(13)${^{\circ}}$. The crystal structure of II has indicated that chromium(III) ion is six-coordinated by four secondary amines of the macrocycle, hydroxide anion and nitrophenolate anion.

• Bulletin of the Korean Chemical Society
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• 제16권10호
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• pp.938-945
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• 1995

Hydrolysis of p-nitrophenyl acetate (PNPA) and p-nitrophenyldiphenyl phosphate (PNPDPP) by N-chloro compounds in micellar solution were studied. N,N'-dichloroisocyanuric acid sodium salt (DCI) in cetyltrimethylammonium chloride (CTACl) micellar solution gave pseudo first-order kinetics. But, DCI in cetyltrimethylammonium bromide (CTABr) micellar solution showed typical series first-order kinetics - fast hydrolysis of the esters and concomitant slow decay of the hydrolyzed product, p-nitrophenolate. The hydrolysis rate was decreased as the hydrophobicity of N-chloro compounds was increased, which is the opposite trend to the usual bimolecular micellar reaction. This curious behavior of the N-chloro compounds in the catalytic hydrolysis of PNPA and PNPDPP in a cationic micellar system can be best explained by participation of counter ions of the surfactants during hydrolysis.

• Bulletin of the Korean Chemical Society
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• 제31권12호
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• pp.3588-3592
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• 2010

Second-order rate constants ($k_N$) have been measured spectrophotometrically for nucleophilic substitution reactions of 2-pyridyl X-substituted benzoates 8a-e with a series of alicyclic secondary amines in $H_2O$ at $25.0{\pm}0.1^{\circ}C$. The $k_N$ values for the reactions of 8a-e are slightly smaller than the corresponding reactions of 4-nitrophenyl X-substituted benzoates 1a-e (e.g., $kN^{1a-e}/k_N^{8a-e}$ = 1.1 ~ 3.1), although 2-pyridinolate in 8a-e is ca. 4.5 $pK_a$ units more basic than 4-nitrophenolate in 1a-e. The Br$\o$nsted-type plot for the aminolysis of 8c (X = H) is linear with $\beta_{nuc}$ = 0.77 and $R^2$ = 0.991 (Figure 1), which is typical for reactions reported previously to proceed through a stepwise mechanism with breakdown of a zwitterionic tetrahedral intermediate $T^{\pm}$ being the rate-determining step (RDS), e.g., aminolysis of 4-nitrophenyl benzoate 1c. The Hammett plot for the reactions of 8a-e with piperidine consists of two intersecting straight lines (Figure 2), i.e., $\rho$ = 1.71 for substrates possessing an electron-donating group (EDG) while $\rho$ = 0.86 for those bearing an electron-withdrawing group (EWG). Traditionally, such a nonlinear Hammett plot has been interpreted as a change in RDS upon changing substituent X in the benzoyl moiety. However, it has been proposed that the nonlinear Hammett is not due to a change in RDS since the corresponding Yukawa-Tsuno plot exhibits excellent linear correlation with $\rho$ = 0.85 and r = 0.62 ($R^2$ = 0.995, Figure 3). Stabilization of substrates 8a-e in the ground state has been concluded to be responsible for the nonlinear Hammett plot.