Kinetics of the reactions of halide anions with carbocations: quantitative energy profiles for s(n)1 reactions

Rate constants for the reactions of Laser flash photolytically generated benzhydrylium ions (diarylcarbenium ions) with halide ions have been determined in various solvents, including neat and aqueous acetonitrile as well as some alcohols. Substitution of the rate constants into the correlation equation log k = s(N + E) yields the nucleophilicity parameters N for the halide ions in different solvents. Linear correlations with negative slopes are found between the nucleophilicity parameters N for Cl(-) and Br(-) in different solvents and the solvent ionizing powers Y of the corresponding solvents. Increasing halide solvation reduces the rates of carbocation/chloride combinations by approximately half as much as it increases the rates of ionizations of benzhydryl chlorides. Comparison of the solvent dependent nucleophilicity parameters N of halide anions and the nucleophilicity parameters N(1) for solvents yields a quantitative prediction of common ion rate depression, as demonstrated by the analysis of a variety of literature reported mass-law constants alpha. Combination of the rate constants for the reactions of benzhydrylium ions with halide ions (k(-)()(1)) reported in this work with the ionization constants of benzhydryl halides (k(1)) and the recently reported rate constants for the reactions of benzhydrylium ions with solvents (k(2)) yields complete quantitative free energy profiles for solvolysis reactions. The applicability of Hammond's postulate for interpreting solvolysis reactions can thus be examined quantitatively.     

Stereoselectivity in cycloaddition of phenylglyoxylonitrile oxide to 7-substituted norbornadienes and 8-substituted 2-azabicyclo[3.2.1]oct-3,6-dienes

The cycloaddition of phenylglyoxylonitrile oxide to the 7-substituted norbornadienes $\text{1}$a-c gives predominantly the endo isomers, but that to the 8-substituted 2-azabicyclo[3.2.1]oct-3,6-dienes $\text{2}$a,b the exo isomers.     

Hypertension does not stimulate the development of hypercholesterolemia or fatty liver induced by a high cholesterol/cholate diet in rats

A high cholesterol/cholate diet induced hypercholesterolemia and fatty liver in both spontaneously hypertensive rats (SHR) and normotensive control rats (WKY). However, in contrast to previous concepts, the levels of cholesterol ester, triacylglycerol and phosphatidylcholine in plasma as well as triacylglycerol in liver were higher in WKY than in SHR fed a normal diet. The high cholesterol/cholate diet elevated the levels of plasma cholesterol, plasma cholesterol ester and hepatic triacylglycerol, and the extent of elevation was significantly higher in WKY than in SHR. Increases both in monoene/saturated ratios, an indication of elevated delta 9-desaturase activity, and in linoleate/arachidonate ratios, a possible indication of impaired desaturation-elongation activity, were observed in hepatic and plasma lipids of both strains fed the high cholesterol/cholate diet. The increases in monoene/saturated ratios were similar in both strains, but the increases in the linoleate/arachidonate ratios were higher for the plasma cholesterol esters of WKY than of SHR. The n-6/n-3 ratios of plasma and hepatic lipids were higher in WKY than in SHR throughout the experiments. These diet-induced changes observed in hepatic and plasma lipids were not reflected in the aortic lipids. Thus, hypertension per se does not promote the development of hyperlipemia and fatty liver induced by a high cholesterol/cholate diet. Our results also suggest that the metabolism of polyenoic fatty acids is different between SHR and WKY.     

Variation of free volume size and content of shape memory polymer — Polyurethane — Upon temperature studied by positron annihilation lifetime techniques and infrared spectroscopy

Positron annihilation lifetime measurement and Fourier transform infrared spectrometry were applied to the study of temperature dependencies of free volume parameters and hydrogen bonds in segmented polyurethane, specially fabricated as a shape memory polymer. The variation of free volumes in amorphous region were correlated to that of hydrogen bonding and the shape memory mechanism of polyurethane is elucidated from a microscopic point of view. The relationship between free volume contents and the formation of hydrogen bonds significantly suggests that the shape memory occurs due to the configurational recovery of the microscopic regulation around urethane bundles of hard segment and consequent restoration of soft-segment in polyurethane.     

Polymerization of cyclic ethers in the presence of maleic anhydride. Part I. Polymerization of trioxane and 3,3-bis(chloromethyl)oxetane by γ-rays,ultraviolet light,and benzoyl peroxide

Cyclic ethers such as trioxane and 3,3-bis(chloromethyl)oxetane have been polymerized easily in the presence of maleic anhydride by the irradiation of γ-rays and ultraviolet light. The polymer formed is a homopolymer of cyclic ether. The rate of polymerization is accelerated by suitable amounts of oxygen which is required to form some active species at the initiation step. The polymerization is inhibited by the addition of a small amount of radical scavenger, thus suggesting a radical initiating mechanism. In addition, the polymerization is easily initiated by benzoyl peroxide even in vacuo at or above 50°C. Diaroyl and diacyl peroxides are also effective, and polymerization also proceeds in the presence of chloromaleic anhydride, exactly in the same manner as in maleic anhydride. On the other hand, it is well known that polymerization of these cyclic monomers rarely occurs with radical catalysts and easily with cationic catalysts in the absence of maleic anhydride. From these results, it may be concluded that the polymerization is brought about by means of a radical–cationic species.     

Synthesis and reactivity of a (mu-1,1-hydroperoxo)(mu-hydroxo)dicopper(II) complex: ligand hydroxylation by a bridging hydroperoxo ligand

A new tetradentate tripodal ligand (L3) containing sterically bulky imidazolyl groups was synthesized, where L3 is tris(1-methyl-2-phenyl-4-imidazolylmethyl)amine. Reaction of a bis(mu-hydroxo)dicopper(II) complex, [Cu2(L3)2(OH)2]2+ (1), with H2O2 in acetonitrile at -40 degrees C generated a (mu-1,1-hydroperoxo)dicopper(II) complex [Cu2(L3)2(OOH)(OH)]2+ (2), which was characterized by various physicochemical measurements including X-ray crystallography. The crystal structure of 2 revealed that the complex cation has a Cu2(mu-1,1-OOH)(mu-OH) core and each copper has a square pyramidal structure having an N3O2 donor set with a weak ligation of a tertiary amine nitrogen in the apex. Consequently, one pendant arm of L3 in 2 is free from coordination, which produces a hydrophobic cavity around the Cu2(mu-1,1-OOH)(mu-OH) core. The hydrophobic cavity is preserved by hydrogen bondings between the hydroperoxide and the imidazole nitrogen of an uncoordinated pendant arm in one side and the hydroxide and the imidazole nitrogen of an uncoordinated pendant arm in the other side. The hydrophobic cavity significantly suppresses the H/D and 16O/18O exchange reactions in 2 compared to that in 1 and stabilizes the Cu2(mu-1,1-OOH)(mu-OH) core against decomposition. Decomposition of 2 in acetonitrile at 0 degrees C proceeded mainly via disproportionation of the hydroperoxo ligand and reduction of 2 to [Cu(L3)]+ by hydroperoxo ligand. In contrast, decomposition of a solid sample of 2 at 60 degrees C gave a complex having a hydroxylated ligand [Cu2(L3)(L3-OH)(OH)2]2+ (2-(L3-OH)) as a main product, where L3-OH is an oxidized ligand in which one of the methylene groups of the pendant arms is hydroxylated. ESI-TOF/MS measurement showed that complex 2-(L3-OH) is stable in acetonitrile at -40 degrees C, whereas warming 2-(L3-OH) at room temperature resulted in the N-dealkylation from L3-OH to give an N-dealkylated ligand, bis(1-methyl-2-phenyl-4-imidazolylmethyl)amine (L2) in approximately 80% yield based on 2, and 1-methyl-2-phenyl-4-formylimidazole (Phim-CHO). Isotope labeling experiments confirmed that the oxygen atom in both L3-OH and Phim-CHO come from OOH. This aliphatic hydroxylation performed by 2 is in marked contrast to the arene hydroxylation reported for some (mu-1,1-hydroperoxo)dicopper(II) complexes with a xylyl linker.     

Stable metallic behavior and antiferromagnetic ordering of Fe(III) d spins in (EDO-TTFVO)2.FeCl4

We report the crystal structure and physical properties of the 2:1 FeCl4- salt of a new donor molecule, EDO-TTFVO. Crystal structure analysis of this salt revealed that the donor molecules formed a beta' '-type two-dimensional conducting layer, and there is a short S...Cl contact between the donor molecules and the FeCl4- ions, which is expected to mediate a strong pi-d interaction. This salt showed a stable metallic conducting behavior down to 0.3 K and an antiferromagnetic ordering at TN approximately 3.0 K, indicating that this salt becomes a new antiferromagnetic molecular metal at ambient pressure. The appearance of the magnetic ordering is considered to originate from the strong pi-d interactions between the donor molecules and the FeCl4- ions because the field dependence of magnetoresistances was remarkably affected below the antiferromagnetic transition temperature.     

Application of chiral bidentate NMR solvents for assignment of the absolute configuration of alcohols: scope and limitation

The ¹³C NMR behaviors of several cyclic and biaryl secondary alcohols as well as acyclic tertiary alcohols have been studied in the chiral bidentate NMR solvent BMBA-p-Me (1). An empirical rule has been advanced to correlate the absolute configuration of each type of alcohols with the ¹³C chemical shift behaviors in (R,R)- and (S,S)-BMBA-p-Me.     

Preparation of poly(arylenediphosphine)s by palladium‐catalyzed polycondensation: Formation of polymer transition‐metal complexes and catalytic reactions

The palladium‐catalyzed polycondensation of aryl diiodides with 1,3‐bis(phenylphosphino)propane afforded poly(arylenediphosphine)s in good yields. Treatment of the polyphosphine with elemental sulfur and hydrogen peroxide efficiently converted the polyphosphine into poly(arylenediphosphine sulfide) and poly(arylenediphosphine oxide), respectively. Treatment of the polyphosphines with Pd(II) and Pt(II) yielded corresponding polymer‐metal complexes with high metal contents. Application of the polymer‐Pd complexes in homogeneous and heterogeneous aryl alkynylation and carbonylation was examined. The polymer‐Pd complexes showed good catalytic activity similar to that of the corresponding low molecular weight Pd complex, and reuse of the polymer catalysts was easily achieved. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2637–2647, 2002     

Seeded polymerization of vinyl acetate using monodisperse poly(vinyl acetate) latex particles

The seeded polymerizations of vinyl acetate, using monodisperse poly(vinyl acetate) latex particles prepared in the absence of emulsifiers with potassium persulfate, have been investigated at 70°C with potassium persulfate as an initiator. New small particles were formed in the system containing a small amount of seed particles, but were not observed in the system containing a large amount of seed particles. The size of the secondary particles increased, and their number decreased, with an increase in the seed particle number. The minimum diameter of PVAc particles, which are stabilized by the sulfate ion groups bound at the end of polymer chains during polymerization, was determined to be 0.12 μm diameter from the limiting total surface area of seed particles which prevented further secondary nucleation. The minimum diameter of the particles increased as the speed of the stirrer increased. The new small particle number calculated using this value agreed well with that formed in the seeded polymerization.