Spectroscopic study of solid-state photoreaction in organic crystal: Photopolymerization of dimethyl ester of α,α′-dicyano-p-phenylenediacrylic acid and diethyl ester of p-phenylenediacrylic acid

Raman spectroscopy has been used to study solid-state photopolymerization reactions in dimethyl ester of α,α′-dicyano-p-phenylenediacrylic acid (p-CPAMe) and diethyl ester of p-phenylenediacrylic acid (p-PDAEt). The reactants and products were characterized by infrared and Raman spectroscopy. Excitation and emission spectra suggest that in p-CPAMe exciton–phonon coupling is strong, but in the other monomer it is very weak. Raman phonon spectroscopic study reveal that in both the samples the reaction mechanism is homogeneous in the initial stages. However, in the later stages the reaction becomes heterogeneous in p-PDAEt. In p-CPAMe the lattice becomes disordered with the progress of polymerization and finally becomes amorphous whereas in p-PDAEt the lattice remains highly ordered. © 1992 John Wiley & Sons, Inc.     

Laser Raman spectroscopic study of photoreaction dynamics in p -chloro cinnamic acid crystal

Raman phonon spectroscopy has been used to study photodimerization reaction inp-chloro cinnamic acid (pCCA) crystal. The β-form of the crystal yields the 4,4′-dichloro-β-truxinic acid dimer. Six distinct low frequency phonon bands are observed in thepCCA monomer crystal. On reaction progress, these bands show a monotonic shift to lower frequencies and broaden out. Finally, in the dimer crystal the phonon spectrum shows two weak broad bands. These results suggest that the reaction is homogeneous in the initial stages and, as the product concentration increases, the lattice becomes highly disordered. The reactant and the product were characterised by infrared and Raman spectroscopy. The disappearance of aliphatic C=C bond stretching vibration and appearance of cyclobutane ring deformation and cyclobutane ring-breathing vibrations on reaction confirm photodimerization by cyclobutane ring formation. The large Stoke's shift between the absorption and emission band suggest strong exciton-phonon coupling in the monomer lattice. This reaction seems to be phonon-mediated.     

Preparation of 1,3-dienyl organotrifluoroborates and their Diels-Alder/cross-coupling reactions

2-BF₃-substituted 1,3-butadienes with potassium and tetrabutyl ammonium counterions have been prepared in gram quantities from chloroprene via a simple synthetic procedure. The potassium salt of this new main group element substituted diene has been characterized by ¹H, ¹³C, ¹¹B, and ¹⁹F NMR and the tetra n-butyl ammonium salt was also characterized by X-ray crystallography. Diels-Alder reactions of these dienes with dienophiles such as ethyl acrylate, methyl vinyl ketone, and N-phenylmaleimide are reported as well as subsequent Pd-catalyzed cross-coupling reactions of those Diels-Alder adducts. 4-Phenyl-2-BF₃-substituted 1,3-diene was prepared by magnesium-halogen exchange from the corresponding 2-bromo and iodo dienes. The 4-phenyl-2-bromo-1,3-butadiene was also characterized by X-ray crystallography. 4-Phenyl-2-BF₃-1,3-butadiene was used in Diels-Alder/cross-coupling reactions and the product of a Diels-Alder reaction with N-phenylmaleimide followed by cross-coupling with 4-bromo-benzonitrile was also characterized by X-ray crystallography.     

An account of the strategies to enhance the water splitting efficiency of noble-metal-free electrocatalysts

The electrolysis of water for hydrogen generation has shown immense promise as an energy conversion technology for the green energy economy.Two concurrently occ...     

Convenient,Mild Catalytic Deprotection of Oximes to Carbonyl Compounds with Hydrogen Peroxide and Iodine Catalyst in Aqueous Acetonitrile

A clean, mild, and efficient catalytic deoximation procedure compatible with several common functional groups has been developed using 30% hydrogen peroxide activated by iodine catalyst in aqueous acetonitrile under essentially neutral conditions. The mechanistic features of an iodonium ion–driven nucleophilic cleavage of oximic C[dbnd]N have been revealed.     

Kinetic Studies on Interaction of Platinum(II) Complexes with an ‘S’ Containing Ligand in Aqueous Medium

The kinetics of the substitution reactions of [Pt(dach)(H₂O)₂]²⁺ and [Pt(en)(H₂O)₂]²⁺ (where ‘dach’ and ‘en’ are cis-1,2-diaminocyclohexane and ethylenediamine, respectively) with excess N,N′-diethylthiourea have been studied in aqueous solution by UV–Vis spectrophotometry. The effect of different N–N spectator ligands on the reactivity of platinum(II) complexes was investigated by studying the water lability of the reactant complexes. The kinetic study has been substantiated by product isolation, IR, NMR and ESI-MS spectral analysis and DFT calculations. The reactions follow normal square-planar substitution mainly in an associative way. Rate parameters have been evaluated under different conditions. The substitution rates of the complexes studied can be tuned through the nature of the N–N chelates, which is important in the development of new active compounds for cancer therapy.     

Numerical investigation on the effect of magnetic field on natural convection heat transfer from a pair of embedded cylinders within a porous enclosure

The present work examines the influence of magnetohydrodynamic field on natural convection phenomena inside a porous square enclosure with a pair of embedded hot circular cylinders. Numerical investigations are performed to understand the effects of interspacing distance between the embedded cylinders, Hartmann number, Rayleigh number and Darcy number on the thermal transport process and the total irreversibility generation. It is observed that the isotherm distribution is strongly affected by the presence of magnetic field although the distribution of streamlines remains independent of the strength of magnetic field. This underlines the fact that magnetic field strongly influences the heat transfer process and entropy generation characteristics. It reveals that the natural convection is suppressed in the presence of a higher magnetic field as evident from the reduction in Nusselt number. It is observed that an increase in the spacing between the cylinders increases the heat transfer rate, and moreover, the effect of the magnetic field on heat transfer is more pronounced at higher interspacing distance between the embedded cylinders. The heat transfer rate increases significantly with the increase in the permeability of the medium. The entropy generation rate is independent of the strength of applied magnetic field. Further, the contribution of the entropy generation owing to friction is found to be negligible in total irreversibility obtained at lower values of Rayleigh number irrespective of Darcy number. However, the contribution of irreversibility owing to heat transfer is found to be minimal at higher values of Rayleigh number.

     

Effect of initial orientation on twinning in commercially pure titanium

Abstract

The effect of initial orientation on twinning micro-mechanisms during tensile deformation of commercially pure titanium has been studied using micro focus X-ray diffraction and electron back scatter diffraction (EBSD) in a scanning electron microscope. Three orientations A, B and C obtained from a rolled and annealed block of commercially pure titanium were deformed in uniaxial tension till failure and the tested specimens were characterised with regard to bulk texture, microstructure and crystal orientation mapping using EBSD. Orientation B along the transverse direction in ND-TD plane exhibits higher strength and lower strain hardening compared to orientations A and C along the rolling direction in TD-RD and ND-RD plane, respectively. This is attributed to different texture of sample B compared to samples A and C leading to dissimilar twinning micro-mechanisms and characteristic variation in nature of twinning. It is observed that limited twin nucleation and prominent lateral growth plays a dominant role in orientation B while multiple twin nucleation with significant non-Schmid behaviour is dominant for the other two orientations. It is proposed from this study that conventional factors associated with twin formation like Schmid factor play a main role in twin nucleation and propagation, however, growth or lateral thickening of the twins is explained by elastic stiffness variation across twins and their parent grains.     

Alkali Metal and Alkaline Earth Metal Complexes with the Bis(borane‐diphenylphosphanyl)amido Ligand – Synthesis,Structures, and Catalysis for Ring‐Opening Polymerization of ϵ‐Caprolactone

The syntheses of lithium and alkaline earth metal complexes with the bis(borane‐diphenylphosphanyl)amido ligand ( 1 ‐ H ) of molecular formulas [{κ²‐N(PPh₂(BH₃))₂}Li(THF)₂] ( 2 ) and [{κ³‐N(PPh₂(BH₃))₂}₂M(THF)₂] [(M = Ca ( 3 ), Sr ( 4 ), Ba ( 5 )] are reported. The lithium complex 2 was obtained by treatment of bis(borane‐diphenylphosphanyl)amine ( 1 ‐ H ) with lithium bis(trimethylsilyl)amide in a 1:1 molar ratio via the silylamine elimination method. The corresponding homoleptic alkaline earth metal complexes 3 – 5 were prepared by two synthetic routes – first, the treatment of metal bis(trimethylsilyl)amide and protio ligand 1 ‐ H via the elimination of silylamine, and second, through salt metathesis reaction involving respective metal diiodides and lithium salt 2 . The molecular structures of lithium complex 2 and barium complex 5 were established by single‐crystal X‐ray diffraction analysis. In the solid‐state structure of 2 , the lithium ion is ligated by amido nitrogen atoms and hydrogen atoms of the BH₃ group in κ²‐coordination of the ligand 1 resulting in a distorted tetrahedral geometry around the lithium ion. However, in complex 5 , κ³‐coordination of the ligand 1 was observed, and the barium ion adopted a distorted octahedral arrangement. The metal complex 5 was tested as catalyst for the ring opening polymerization of ?‐caprolactone. High activity for the barium complex 5 towards ring opening polymerization (ROP) of ?‐caprolactone with a narrow polydispersity index was observed. Additionally, first‐principle calculations to investigate the structure and coordination properties of alkaline earth metal complexes 3 – 5 as a comparative study between the experimental and theoretical findings were described.     

A heterometallic, heterovalent Cu(I)/Sn(II/IV)/S cluster with an unprecedented Cu4Sn core and stannacyclopentane units

[(Ph3PCu(I))6{(CH2)4Sn(IV)S2}6Cu(I)4Sn(II)], a walnut-type, heterometallic, heterovalent cluster, as confirmed by density functional theory calculations, was obtained under reductive solvothermal conditions and features an unprecedented metalloid core within a metal sulfide shell and an organic surface.