Time-resolved pH jump study of photochemical cleavage and release of carboxylic acids from α-keto amides

Time-resolved pH jump experiments, using laser flash photolysis and bromocresol green as an indicator, showed that photochemical cleavage and release of carboxylic acids from various α-keto amides derivatives in aqueous media occurs on the microsecond timescale (18-136 μs), depending on carboxylate leaving group ability.     

Conversion of substituted 5‐aryloxypyrazolecarbaldehydes into reduced 3,4′‐bipyrazoles: synthesis and characterization,and the structures of four precursors and two products,and their supramolecular assembly in zero,one and two dimensions

The reaction of 5‐chloro‐3‐methyl‐1‐phenyl‐1H‐pyrazole‐4‐carbaldehyde with phenols under basic conditions yields the corresponding 5‐aryloxy derivatives; the subsequent reaction of these carbaldehydes with substituted acetophenones yields the corresponding chalcones, which in turn undergo cyclocondensation reactions with hydrazine in the presence of acetic acid to form N‐acetylated reduced bipyrazoles. Structures are reported for three 5‐aryloxycarbaldehydes and the 5‐piperidino analogue, and for two reduced bipyrazole products. 5‐(2‐Chlorophenoxy)‐3‐methyl‐1‐phenyl‐1H‐pyrazole‐4‐carbaldehyde, C₁₇H₁₃ClN₂O₂, (II), which crystallizes with Z′ = 2 in the space group P, exhibits orientational disorder of the carbaldehyde group in each of the two independent molecules. Each of 3‐methyl‐5‐(4‐nitrophenoxy)‐1‐phenyl‐1H‐pyrazole‐4‐carbaldehyde, C₁₇H₁₃N₃O₄, (IV), 3‐methyl‐5‐(naphthalen‐2‐yloxy)‐1‐phenyl‐1H‐pyrazole‐4‐carbaldehyde, C₂₁H₁₆N₂O₂, (V), and 3‐methyl‐1‐phenyl‐5‐(piperidin‐1‐yl)‐1H‐pyrazole‐4‐carbaldehyde, C₁₆H₁₉N₃O, (VI), (3RS)‐2‐acetyl‐5‐(4‐azidophenyl)‐5′‐(2‐chlorophenoxy)‐3′‐methyl‐1′‐phenyl‐3,4‐dihydro‐1′H,2H‐[3,4′‐bipyrazole] C₂₇H₂₂ClN₇O₂, (IX) and (3RS)‐2‐acetyl‐5‐(4‐azidophenyl)‐3′‐methyl‐5′‐(naphthalen‐2‐yloxy)‐1′‐phenyl‐3,4‐dihydro‐1′H,2H‐[3,4′‐bipyrazole] C₃₁H₂₅N₇O₂, (X), has Z′ = 1, and each is fully ordered. The new compounds have all been fully characterized by analysis, namely IR spectroscopy, ¹H and ¹³C NMR spectroscopy, and mass spectrometry. In each of (II), (V) and (IX), the molecules are linked into ribbons, generated respectively by combinations of C—H…N, C—H…π and C—Cl…π interactions in (II), C—H…O and C—H…π hydrogen bonds in (V), and C—H…N and C—H…O hydrogen bonds in (IX). The molecules of compounds (IV) and (IX) are both linked into sheets, by multiple C—H…O and C—H…π hydrogen bonds in (IV), and by two C—H…π hydrogen bonds in (IX). A single C—H…N hydrogen bond links the molecules of (X) into centrosymmetric dimers. Comparisons are made with the structures of some related compounds.     

Kinetics and Mechanism of Oxidation of Some Substituted Benzhydrols by <Emphasis Type="Italic">N</Emphasis>-Bromosuccinimide

N-bromosuccinimide (NBS) oxidation of some substituted benzhydrols (4-Cl-, 4-Me-, 4-OMe-, 4-NO²⁻, 4,4′-dimethyl-, 4,4′-dichloro-, 4,4′-dimethoxy-, and 4-methyl-2-nitro-) yields corresponding benzophenones in the presence of Hg(OAc)₂. The reaction is first-order in [NBS], [substrate], and [H⁺]. A study on the primary kinetic hydrogen isotope effect and solvent isotope effect suggest that C-H and O-H stretching frequencies are affected in the transition state. Activation parameters for the rate-determining step have been evaluated. The results are in accord with the linear free energy relationship (LFER). The linear plot of log(k _obs/k ₀) vs. σ⁺ (ρ = −0.69)and Bunnett plots support the existence of proton-transfer in the rate-determining step. Rate behavior in different solvent compositions suggests dipolar-dipolar interaction in the absence of acid and ion-dipolar interaction in the presence of acid. Two different mechanisms have been suggested: cyclic transition state with unprotonated N-bromosuccinimide (NBS) in the absence of acid and noncyclic transition state with protonated NBS in the presence of acid.__________From Kinetika i Kataliz, Vol. 46, No. 3, 2005, pp. 360–365.Original English Text Copyright © 2005 by Hiran, Malkani, Rathore.This article was submitted by the authors in English.     

Isolation and X-ray structural characterization of tetraisopropylpyrene cation radical

A practical synthesis of 1,3,6,8-tetraisopropylpyrene and the isolation and X-ray structural characterization of its monomeric cation radical salt are described.     

Duplexiphane: a polyaromatic receptor containing two adjoined Delta-shaped cavities for an efficient hopping of a single silver cation

A simple synthesis of a polyaromatic receptor (i.e., duplexiphane) containing two adjoined Delta-shaped cavities is accomplished via an intramolecular (double) McMurry coupling, and its structure is established by X-ray crystallography. The binding of silver cation to duplexiphane showed that it binds only a single silver cation with significantly higher efficiency (>100 times) than a model compound containing only one pi-prismand-like cavity, and the single silver cation hops intramolecularly between the two adjoined cavities in duplexiphane.     

Photochemical elimination of leaving groups from zwitterionic intermediates generated via electrocyclic ring closure of alpha,beta-unsaturated anilides

Methacrylanilides, ArN(CH3)COC(CH2LG)=CH2, with allylic leaving groups (LG(-) = BocAla, PhCO2(-), PhCH2CO2(-), PhO(-)) undergo photochemical electrocyclic ring closure to produce a zwitterionic intermediate. Further reaction of the intermediate results in expulsion of the leaving group to give an alpha-methylene lactam as the major product. In addition, a lactam product that retains the leaving group is formed via a 1,5-H shift in the intermediate. Elimination of the leaving group is generally preferred, even for LG(-) = PhO(-), although in benzene as the solvent the lactam retaining the phenolate group becomes the sole photoproduct. The electrocyclic ring closure occurs in the singlet excited-state for the para-COPh-substituted anilide derivative and is not quenched by 0.15 M piperylene or 0.01 M sodium 2-naphthalenesulfonate (2-NPS) as triplet quenchers. Comparable concentrations of 2-NPS strongly quench the transient absorption of the triplet excited state observed at 450-700 nm according to laser flash photolysis experiments. In aqueous media, quantum yields for total products are insensitive to leaving group ability, and Phi(tot)(para-CO2CH3) = 0.04-0.06 at 310 nm and Phi(tot)(para-COPh) = 0.08-0.1 at 365 nm, for which Phi(isc) = 0.15.     

Ein Beitrag zum Einfluß des Stoffüberganges auf eine erzwungene Konvektion an einer fluiden Phasengrenze

The interfacial-dynamic behaviour of a fluid two-phase-system with mass transfer was investigated under influence of forced convection in the manner of flat jets directed to the interface. The tangential velocities were measured at a characteristic point near to the interface air/water or in the interface itself using a Laser-Doppler-Velocimeter in dependence on the velocities of jets into two phases in both cases with and without transfer of acetone. The variations of velocities due to the interfacial effects are only detectable at small velocities of the jets. They are discussed by model conceptions and compared with the results of a theoretical research of heat transfer in a fluid two-phase-system (Interfacial-dynamic surface renewal model).     

A Review on Mechanical Behavior of FRP Composites at Different Loading Speeds

Fiber-reinforced polymer (FRP) composites are increasingly becoming suitable and durable materials in the repair and replacement of traditional metallic materials. The built-in promise of performance assurance and retention of structural integrity in harsh and hostile environments of these materials certainly offers an alternative and attractive avenue for a wider range application to explore its potential to the zenith. The toughest challenge faced by material scientists is to assess and ascertain its behavioral log in a range of loading rates. The heterogeneity and responses of multiple distinct phases to varying loading conditions are most often complex and far away from comprehensive conclusion. Furthermore, composites with common structural polymer matrices quite often absorb moisture during service period. Then, FRPs become a much more complex system to comprehend its sensitivity to experimental variation. The present article emphasizes the need for understanding this perpetual problem of FRPs which might pose a threat to its prospects.     

The HOMO Nodal Arrangement in Polychromophoric Molecules and Assemblies Controls the Interchromophoric Electronic Coupling

Triptycenes spontaneously assemble into two‐dimensional networks in which long‐range charge transport is facilitated by the extensive electronic coupling through the triptycene framework (intramolecularly) and by cofacial π‐stacking (intermolecularly). While designing and synthesizing next‐generation triptycenes containing polyaromatic chromophores, the electronic coupling amongst the chromophores was observed to be highly dependent on the nature and position of the substituents. Herein, we demonstrate using hexaalkoxytriptycenes that the electronic coupling amongst the chromophores is switched on and off by a simple repositioning of the substituents, which alters the nodal arrangement of the HOMOs of the individual chromophores. A visual inspection of the HOMOs can thus provide a ready evaluation of the electronic coupling in polychromophoric molecules/assemblies, and will serve as an important tool for the rational design of modern charge‐transport materials.     

HYDROXYALKANESULFONYL CHLORIDES FROM CHLORINATION OF HYDROXYALKANESULFINATE SALTS IN A NONPOLAR MEDIUM: 3-HYDROXY-1-PROPANESULFONYL AND 4-HYDROXY-1-BUTANESULFONYL CHLORIDES

Abstract

3-Hydroxy-1-propanesulfonyl chloride (1b) was obtained for the first time (admixed with 10% of propane sultone, 2b) by chlorination of a dichloromethane suspension of sodium 3-hydroxy-1-propanesulfinate (3b). 4-Hydroxy-1-butanesulfonyl chloride (1c) containing 13% butane sultone (2c) was prepared similarly from 3c. The cyclizations of 1b and 1c in CDCl₃ containing 1-butanol (0.9 M) showed first order rate constants of 1.4 × 10^?4 and 6.4 × 10^?5 s^?1, corresponding to effective concentrations of 4.5 × 10² and 2.1 × 10² M, respectively. Reaction of triethylamine in ethanol-d (a) with 1b gave exclusively the undeuterated sultone (2b), evidently by a direct cyclization, and (b) with 1c produced mainly ethyl 4-hydroxy-1-butanesulfonate largely monodeuterated at the α-position, and presumably formed by way of the sulfene (6c).