Reactions of Aliphatic Diazo Compounds: VI. Reactions of Diazomethane and Ethyl Diazoacetate with (E)-2-Arylmethylene-1,2,3,4-tetrahydronaphthalen-1-ones

Diazomethane and ethyl diazoacetate add to (E)-2-arylmethylene-1,2,3,4-tetrahydronaphthalen-1-ones in a regio- and stereoselective fashion, yielding the corresponding 4'-aryl-1,2,3,4,4',5'-hexahydro-3'H-naphthalene-2-spiro-3'-pyrazol-1-ones. The products formed by addition of ethyl diazoacetate undergo isomerization into 4,5-dihydro-1H-pyrazole derivatives.     

Paradigms and Paradoxes: Energetics of Aqueous Oxyanions of Nonmetals and Metalloids

The enthalpies of formation of simple nonmetal or metalloid oxyanions in aqueous solution are discussed. Archival values are cited and estimates are made. Trends prove evasive.     

Paradoxes and Paradigms: Aqueous Polynuclear Oxyanions of Sulfur and Homologous Series

The enthalpies of formation of several series of aqueous polynuclear oxyanions of sulfur are discussed. In this context we briefly discuss the nature of homologous series.     

Reactions of Aliphatic Diazo Compounds: III. Reaction of Ethyl Diazoacetate with 1,3-Diarylpropenones

Ethyl diazoacetate adds to 1,3-diarylpropenones in a regioselective fashion to give intermediate 4,5-dihydro-3H-pyrazole derivative; 1,3-hydride shift in the latter leads to formation of isomeric ethyl 4-aryl- 5-aroyl-4,5-dihydro-1H-pyrazole-3-carboxylate and ethyl 4-aryl-3-aroyl-4,5-dihydro-1H-pyrazole-5-carboxylate at a ratio of 5:1. Thermolysis of these products is not stereospecific; as a result, three isomeric substituted ethyl cyclopropanecarboxylates and 2-pyranone derivative are formed.     

Paradigms and Paradoxes: Resonance Stabilization in Diazophenoxides (Quinone Diazides)

Diazophenoxides (quinone diazides) constitute an interesting class of compounds that are seemingly high-energy species on the nonaromatic/aromatic interface. With appropriate substitution and/or annelation, they have found use in the fields of explosives, medicine, and photolithography. Thermochemical information about them is sparse. To aid further understanding of these important chemical species, the current paper discusses a few extant enthalpies of formation from which we tentatively derive a resonance energy of ca. 15 kJ-mol^–1 for the parent, p-species, 4-diazo-2,5-cyclohexadiene-1-one. Interestingly, this value is nearly identical to that recently found for the likewise conjugated diazo compound, ethyl diazoacetate.     

Paradigms and Paradoxes: Common and Maximum Accessible Oxidation States of the Elements

Common and accessible oxidation states of numerous nonmetals and transition metals in compounds with high oxidation state are discussed. These oxidation state concepts are generally, disappointingly and surprisingly elusive.     

Paradigms and Paradoxes: Aspects of the Energetics of Carboxylic Acids and Their Anhydrides

Making use of the enthalpies of formation of the well-established acetic acid and acetic anhydride, the energetics of other carboxylic acid anhydrides (with four or fewer carbons) are discussed. Some of these species are also well known, such as succinic and maleic anhydride. Others are less well known, such as ketene and carbon suboxide and even diatomic carbon and malonic anhydride. Still others are more evasive, such as the classical anhydrides of formic and oxalic acid.     

Paradigms and Paradoxes: Thoughts on the Enthalpy of Formation of Guanidine and Its Monosubstituted Derivatives

Despite their seeming simplicity, substituted guanidines have not particularly caught the attention of the thermochemical community. The current paper compares the enthalpy of formation of solid substituted guanidines with correspondingly substituted benzenes, also as solids.     

Paradigms and Paradoxes: The Solubility of AgCl in Water: Some Thermochemical Issues of Aqueous Ag+ Ion

It is well established in the pedagogical literature that AgCl is insoluble in water while NaCl and KCl are soluble: applications of this difference are made in elementary studies of both qualitative and quantitative analysis. What is usually left unsaid, however, is why AgCl is so much less soluble than NaCl or KCl. This brief note addresses this issue in terms of the thermochemistry of these three metal chlorides and constituent ions as found in their solid salts, aqueous solutions and gaseous diatomic molecules.     

Paradigms and Paradoxes: Exothermicity of Some Reactions Involving the Noble Gas Fluorides and Oxides

It has long been known that the oxidizing/fluorinating power of noble gas fluorides increases in the order XeF₂ < XeF₄ < XeF₆ < KrF₂. While this does not initially appear surprising, a more careful investigation based on enthalpy and kechanistic considerations show some unexpected features. Reconciliation of these features also provides some understanding of the explosive nature of the sole isolable, noble gas oxides, XeO₃ and XeO₄.     

Paradigms and Paradoxes: Additive trends in the absolute entropy of monoxides and homonuclear diatomic molecules

Structural Chemistry - In general, entropy is not additive for the system of a single molecule. We show this by demonstrating that the entropy of a monoxide species, before and after subtracting...     

Paradigms and Paradoxes: Fractional and Other Non-integer Charges in Chemistry—an Understanding of Aromaticity

Structural Chemistry - In the current study, the energetics of fractionally (and indeed arbitrary non-integer) charged species is explicitly discussed for the enhanced understanding of aromaticity...     

Direct Asymmetric Aldol Type Reaction with Ethyl Diazoacetate: Stereoselective Synthesis of α, β-Dihydroxy Esters

Enantioselective aldol condensation under catalytic condition remains a challenging task in modern organic synthesis, and numerous efforts have been directed to this area. In particular, the direct catalytic asymmetric aldol reaction is very attractive considering the requirement of atom efficiency. This has been studied only recently, and several very practical processes have been developed. We have recently initiated a study on the direct asymmetric aldol type reaction with ethyl diazoacetate as nucleophile. Moderate enantioselectivities (65% ～91% ee ) were achieved in the condensation of aldehydes with ethyl diazoacetate catalyzed by the chiral complex of BINOL derivatives-Zr (OBu- t )4. [1]     

Paradigms and Paradoxes: The Energetics of <Emphasis Type="Italic">N</Emphasis>-Acylimines

N-Acylimines have the functional group –C(O)–N=C and so appear as formally simple derivatives of both amides and of imines. Nonetheless, these are relatively unstudied species and seemingly unstable to hydrolysis and rearrangement. Reaction chemistry and thermochemical reasoning show that N-acylimines are not amides.     

Comparative Analysis of Acyclovir Esters Stability in Solutions: The Influence of the Substituent Structure,Kinetics, and Steric Effects

Reversed‐phase high‐performance liquid chromatography has been applied to the determination of acyclovir (ACV) esters such as acetate, isobutyrate, pivalate, ethoxycarbonate, and nicotinate. All analyses were carried out at laboratory temperature using a column LiChrospher RP‐18 (250 × 4 mm, 5 µm) and a proper mobile phase consisting of acetonitrile and phosphate buffer (pH 6 or 6.7) or acetonitrile and potassium dihydrogen phosphate, and acetic acid. The methods were validated by the determination of the following parameters: selectivity, precision, accuracy, and linearity. Kinetic studies on the hydrolysis were investigated in solutions at 310 K over the pH range 0.42–1.38. The pH‐profiles indicated specific acid‐catalyzed and spontaneous water‐catalyzed degradation. The stability of the studied ACV esters were determined not only by steric factors. In the case of ethoxycarbonyl ester of ACV, the hydrolysis was a two‐step reaction.     

The Role of the Interface in Thin Film and Droplet Accelerated Reactions Studied by Competitive Substituent Effects

Based on a study of competitive substituent effects in a Claisen–Schmidt reaction, interfacial effects have been shown to play an important role in accelerated reactions that occur in thin films and droplets. A role for the interface in an accelerated C?C bond‐formation reaction between 6hydroxy‐1‐indanone and aromatic aldehydes is indicated by cooperative interactions between p‐methylbenzaldehyde and p‐nitrobenzaldehyde. Additional acceleration over that occurring in bulk reactions is seen for p‐methylbenzaldehyde, but only in the presence of p‐nitrobenzaldehyde. A decrease in the degree of acceleration is detected when the reaction is forced electrostatically to occur inside the thin film, and the interface is shown to participate in the accelerated reactions. This experimental evidence for interfacial thin film and droplet acceleration supports a recent model and builds on earlier work which locates molecules within evaporating droplets in electrosprays.     

Paradigms and Paradoxes:Estimation of the Enthalpies of Formation of Some Common,Solid-Phase Compounds of Considerable Theoretical Importance

The enthalpies of formation of the following solid-state species are estimated: calcium carbonate, muscovite, graphite, cellulose, and silicon, which, as found in chalk, slate, pencil lead, paper, and integrated circuits, are key reagents in numerous theoretical studies. Agreement between theory and experiment is within 40 kJ mol^–1.     

Self-Promoted N-Glycosylation: Extended Substrate Scope and Substituent Effects

A self-promoted glycosylation method for the stereoselective formation of β-glucosides from a substrate library of glycosyl trichloroacetimidate glycosyl donors and glycosyl acceptors is presented. The simple two-component reaction takes place at elevated temperatures, without the addition of any additives or catalysts. After a simple basic workup, N-glycosides were obtained in good yields and with high β-selectivity and hence this method allows for easy access to glycoconjugates under very mild conditions. The influences of neighboring group participation and substituents, in both the glycosyl donor and acceptor, were studied. Kinetic data were obtained from in situ IR and these were used for a Hammett study. A connection between the pK_a of the acceptor and reaction rate was found and new mechanistic insight in self-promoted glycosylations gained.     

Ligand Steric and Fluoroalkyl Substituent Effects on Enchainment Cooperativity and Stability in Bimetallic Nickel(II) Polymerization Catalysts

The synthesis and characterization of two neutrally charged bimetallic Ni(II) ethylene polymerization catalysts, {2,7-di-[2,6-(3,5-di-methylphenylimino)methyl]1,8-naphthalenediolato}-bis-Ni(II) (methyl)(trimethylphosphine) [(CH(3) )FI(2) -Ni(2) ] and {2,7-di-[2,6-(3,5-di-trifluoromethyl-phenylimino)methyl]-1,8-naphthalenediolato}-bis-Ni(II) (methyl)(trimethyl-phosphine) [(CF(3) )FI(2) -Ni(2) )], are reported. The diffraction-derived molecular structure of (CF(3) )FI(2) -Ni(2) reveals a Ni???Ni distance of 5.8024(5)??. In the presence of ethylene and Ni(COD)(2) or B(C(6) F(5) )(3) co-catalysts, these complexes along with their monometallic analogues [2-tert-butyl-6-((2,6-(3,5-dimethylphenyl)phenylimino)methyl)-phenolate]-Ni(II) -methyl(trimethylphosphine) [(CH(3) )FI-Ni] and [2-tert-butyl-6-((2,6-(3,5-ditrifluoromethyl-phenyl)phenylimino)methyl)phenolato]-Ni(II) -methyl-(trimethylphosphine) [(CF(3) )FI-Ni], produce polyethylenes ranging from highly branched M(w) =1400 oligomers (91?methyl branches per 1000?C) to low branch density M(w) =92?000 polyethylenes (7?methyl branches per 1000?C). In the bimetallic catalysts, Ni???Ni cooperative effects are evidenced by increased product polyethylene branching in ethylene homopolymerizations (～3× for (CF(3) )FI(2) -Ni(2) vs. monometallic (CF(3) )FI-Ni), as well as by enhanced norbornene co-monomer incorporation selectivity, with bimetallic (CH(3) )FI(2) -Ni(2) and (CF(3) )FI(2) -Ni(2) enchaining approximately three- and six-times more norbornene, respectively, than monometallic (CH(3) )FI-Ni and (CF(3) )FI-Ni. Additionally, (CH(3) )FI(2) -Ni(2) and (CF(3) )FI(2) -Ni(2) exhibit significantly enhanced thermal stability versus the less sterically encumbered dinickel catalyst {2,7-di-[(2,6-diisopropylphenyl)imino]-1,8-naphthalenediolato}-bis-Ni(II) (methyl)(trimethylphosphine). The pathway for bimetallic catalyst thermal deactivation is shown to involve an unexpected polymerization-active intermediate, {2,7-di-[2,6-(3,5-di-trifluoromethyl-phenylimino)methyl]-1-hydroxy,8-naphthalenediolato-Ni(II) (methyl)-(trimethylphosphine).