Kinetic evidence of a common mechanism in the oxidations of diethyl sulfide by dichromates and halochromates of heterocyclic bases

The oxidations of diethyl sulfide by potassium dichromate, pyridinium dichromate, quinolinium dichromate, imidazolium dichromate, nicotinium dichromate, isonicotinium dichromate, pyridinium fluorochromate, quinolinium fluorochromate, imidazolium fluorochromate, pyridinium chlorochromate, quinolinium chlorochromate, and pyridinium bromochromate follow identical kinetic orders—first‐order each with respect to the chromium(VI) reagents, sulfide and hydrogen ion, and moderately inhibited by manganese(II) ion. The energy of activation varies linearly with the logarithm of frequency factor and so does the enthalpy of activation with the entropy of activation. Also, the activation free energies do not differ significantly. The dichromates and halochromates of heterocyclic bases oxidize diethyl sulfide via a common mechanism. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 1–8, 2003     

Photon interaction studies using 241Am γ-rays

We have carried out some photon interaction measurements using 59.54 keV γ-rays from a ²⁴¹Am source. These include γ attenuation studies as well as photoelectric absorption studies in various samples. The attenuation studies have been made using leaf and wood samples, samples like sand, sugar etc., which contain particles of varying sizes as well as pellets and aqueous solutions of rare earth compounds. In the case of the leaf and wood samples, we have used the γ-ray attenuation technique for the determination of the water content in fresh and dried samples. The variation of the attenuation coefficient with particle size has been investigated for sand and sugar samples. The attenuation studies as well as the photoelectric studies in the case of rare earth elements have been carried out on samples containing such elements whose K-absorption edge energies lie below and close to the γ-energy used. Suitable compounds of the rare earth elements have been chosen as mixture absorbers in these investigations. A narrow beam good geometry set-up was used for the attenuation measurements. A well-shielded scattering geometry was used for the photoelectric measurements. The mixture rule was invoked to extract the values of the mass attenuation coefficients for the elements from those of the corresponding compounds. The results are consistent with theoretical values derived from the XCOM package.     

Kinetics and mechanism of oxidation of allyl alcohol byN-bromosuccinimide

The kinetics of oxidation of allyl alcohol byN-bromosuccinimide (NBS) has been studied at 35 °C in aqueous medium. The reaction shows first order dependence on bothNBS and allyl alcohol. In fairly high acid concentration, there is no change in the rate of the reaction but at low acid concentration, the rate is considerably enhanced. There is no primary salt effect. At varying mercuric acetate concentrations, the rate constant remains the same. But in the absence of mercuric acetate, the rate is enhanced. The kinetic parameters,E _a,Arrhenius factorA, H, G and S have been calculated. A rate law in agreement with experimental results has been derived. A mechanism is proposed.

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Kinetik und Mechanismus der Oxidation von Allylalkohol mixN-Bromsuccinimid

Zusammenfassung Die Kinetik der Oxidation von Allylalkohol mitN-Bromsuccinimid (NBS) wurde bei 35 °C in wäßrigem Medium untersucht. Die Reaktion zeigt erste Ordnung gegenüberNBS und Allylalkohol. Bei relativ hoher Säurekonzentration zeigt sich keine Änderung der Reaktionsgeschwindigkeit, bei niedriger Säurekonzentration wird die Reaktionsgeschwindigkeit beträchtlich erhöht. Es wurde kein primärer Salzeffekt festgestellt. Bei varriierender Quecksilberacetatkonzentration bleibt die Reaktionsgeschwindigkeit gleich, bei Abwesenheit von Quecksilberacetat wird jedoch die Geschwindigkeitskonstante erhöht. Die kinetischen Parameter,E _a, derArrheniusfaktorA, H , G und S wurden bestimmt. Ein Geschwindigkeitsgesetz in Übereinstimmung mit den experimentellen Befunden wurde abgeleitet und ein Mechanismus vorgeschlagen.

     

Cooperativity and cluster growth patterns in acetonitrile: A DFT study

Cooperativity in intermolecular interactions and cluster growth patterns of acetonitrile has been studied using M06L density functional theory. Cyclic, ladder‐type, stacked, cross‐stacked, and mixed patterns are studied. Total interaction energy (E_int) and interaction energy per monomer (E_m) show maximum stability and cooperativity in stacked clusters followed by cross‐stacked ones. As cluster size increased, magnitude of E_m showed significant increase. Compared to E_m of dimer (?2.97 kcal/mol), the increase is 2.6‐fold for 27mer . Higher stabilization in larger clusters is attributed to strong cooperativity in intermolecular C? H···N and dipolar interactions. Enhanced cooperativity in stacked structures is supported by atoms‐in‐molecule electron density (ρ) data. Sum of ρ at intermolecular bond critical points is the highest for stacked clusters. Further, area of negative‐valued molecular electrostatic potential is linearly related with E_int and showed the lowest value in stacked followed by cross‐stacked clusters, indicating maximum utilization of lone pair density and maximum cooperativity in such growth patterns. A red shift in the average C? N stretching frequencies with increase in the number of monomers and its direct correlation with E_int in stacked clusters also supported their stability. Further, two known crystal patterns of acetonitrile (α and β) with 16 monomers are optimized and compared with the most stable hexadecamer pattern and are found to show lower values for E_int and E_m compared to the latter. Based on this result, we predict the existence of a third crystal pattern for acetonitrile which will be more ordered and more stable than α and β forms. © 2014 Wiley Periodicals, Inc.     

Gelation Kinetics-Structure Analysis of pH-triggered Low Molecular Weight Hydrogelators

Properties such as shear modulus, gelation time, structure of supramolecular hydrogels are strongly dependent on self-assembly, gelation triggering mechanism and processes used to form the gel. In our work we extend reported rheology analysis methodologies to pH-triggered supramolecular gels to understand structural insight using a model system based on N−N’ Dibenzoyl-L-Cystine pH-triggered hydrogelator and Glucono-δ-Lactone as the trigger. We observed that Avrami growth model when applied to time-sweep rheological data of gels formed at lower trigger concentrations provide estimates of fractal dimension which agree well compared with visualization of the microstructure as seen via Confocal Laser Scanning Microscopy, for a range of gelator concentrations.     

Structure-reactivity correlation of anilines in acetic acid

The oxidation of aniline in glacial acetic acid with percarbonate, a dry carrier of hydrogen peroxide, is a second-order reaction conforming to the isokinetic relationship. The hitherto followed method of correlation of the reaction rates in terms of the structure-reactivity relationships is unsatisfactory and erroneous. But the reaction rates of molecular anilines, obtained for the first time, conform to the structure-reactivity relationships.     

Crystal structure and spectroscopy of a hydrogen-bridged one-dimensional Cu(II) complex containing both octahedral and square pyramidal geometries in the same unit cell

Single crystals of the helical hydrogen-bridged one-dimensional Cu(II) complex, [Cu(stpy)₂(CH₃COO)₂(H₂O)₂] (1) [Cu(stpy)₂(CH₃COO)₂(H₂O)] (2), are prepared and characterized by elemental and thermal analyses, IR, electronic and X-ray crystal structure determination. The crystals are monoclinic, of space group C2/c, with unit cell parameters a = 31.842(7) Å, b = 5.9829(10) Å, c = 30.970(14) Å, = 111.78(3)°, Z = 4. The asymmetric unit contains two different types of Cu(II) polyhedra, namely, octahedron and square pyramid within the same unit cell. 1 has elongated octahedral geometry with two nitrogen atoms from stpy and two oxygen atoms from synmonodentate acetate ligands, transcoordinated to Cu(II) in the basal plane. The oxygen atoms of the two water molecules occupy the axial positions. 2 has Cu(II) coordination polyhedra similar to 1, except that only one of the apical positions is occupied by a water molecule. The structure consists of two independent linear chains, one involving octahedral (1) and the other involving square-pyramidal (2) polyhedra, held by hydrogen bridges. The Cu–Cu intra- and interchain separations in both 1 and 2 are 5.983 and 8.214 Å. The unit cell packing shows weak -stacking between adjacent coordinated stpy ligands in the chain, resulting in ladder-type structure. Further, the extended packing reveals helical arrangement of Cu(II) polyhedra in the lattice.     

A Comparative Study of Electrochemical Reduction of 4‐Nitrophenyl Covalently Grafted on Gold and Carbon

4‐Nitrophenyl layers were grafted on gold and glassy carbon surfaces by electrochemical reductive adsorption of the corresponding diazonium salt. Electrochemical conversion efficiencies of 4‐nitrophenyl moieties to 4‐aminophenyl moieties on gold versus on glassy carbon in a protic medium were investigated using X‐ray photoelectron spectroscopy (XPS). In total contrast to all previous comparative studies showing greater electrochemical reactivity of aryl diazonium salt‐derived layers on gold than on glassy carbon, a much lower rate of conversion to 4‐aminophenyl was observed on gold than on glassy carbon by both cyclic voltammetry (CV) and chronoamperometry (CA) methods. The lower electron transfer rate during conversion observed on gold versus glassy carbon was proposed to be due to a mechanism related to the molecular structure rearrangement of 4‐nitrophenyl during the process on glassy carbon. However, whilst complete conversion of 4‐nitrophenyl to 4‐aminophenyl on gold by chronoamperometry was achieved, on glassy carbon complete reduction could not be achieved under the same conditions.