Reactivity of conformationally constrained bispropargyl sulfones: complete preference for 6π-electrocyclization process

The reactivity of a series of conformationally constrained bispropargyl sulfones with an ortho alkenyl moiety was studied. Under basic condition, these molecules underwent isomerization, first to monoallene followed by 6π-electrocyclization (6π-EC). Another cycle of isomerization and 6π-EC gave the bis naphthyl sulfones. No Garratt–Braverman (GB) Cyclization product could be isolated even on easing up the strain. Computations with DFT (at BP86-D3/def2-SVP level) indicated that, it is energetically more favorable for the initially formed monoallenic intermediate to undergo electrocyclization rather than isomerize to bisallene. This is in contrast to the acyclic unconstrained counterpart, where isomerization to bisallene is preferred and competing GBC/6π-EC of bisallenes results in mixture of products.     

Dielectric behavior and transport properties of ZnO nanorods

Highly optical, good crystalline and randomly aligned ZnO nanorods were synthesized by the hydrothermal method. The dielectric properties of ZnO nanorods were attributed to the interfacial polarization at low frequencies (below 10 kHz) and orientational polarization at higher frequencies. The observed ω^(n?1) dependence of dielectric loss was discussed on the basis of the Universal model of dielectric response. Dielectric loss peak was composed of the Debye like loss peak at higher frequencies and interfacial loss peak at lower frequencies. Charge transport through the grain and grain boundary region was investigated by impedance spectroscopy. At higher temperatures the conductivity of the nanorod was mainly through the grain interior and the overall impedance was contributed by the grain boundary region. The activation energy of nanorod was calculated as 0.078 eV, which is slightly higher than the reported bulk value.     

Non‐Radiative Energy Transfer Mediated by Hybrid Light‐Matter States

We present direct evidence of enhanced non‐radiative energy transfer between two J‐aggregated cyanine dyes strongly coupled to the vacuum field of a cavity. Excitation spectroscopy and femtosecond pump–probe measurements show that the energy transfer is highly efficient when both the donor and acceptor form light‐matter hybrid states with the vacuum field. The rate of energy transfer is increased by a factor of seven under those conditions as compared to the normal situation outside the cavity, with a corresponding effect on the energy transfer efficiency. The delocalized hybrid states connect the donor and acceptor molecules and clearly play the role of a bridge to enhance the rate of energy transfer. This finding has fundamental implications for coherent energy transport and light‐energy harvesting.     

PET-SWNT nanocomposites through ultrasound assisted dissolution-evaporation

Poly(ethylene terephthalate) (PET) based nanocomposites have been prepared with single walled carbon nanotubes (SWNTs) through an ultrasound assisted dissolution-evaporation method. Differential scanning calorimetry studies showed that SWNTs nucleate crystallization in PET at weight fractions as low as 0.3%, as the nanocomposite melt crystallized during cooling at temperature 24 °C higher than neat PET of identical molecular weight. Isothermal crystallization studies also revealed that SWNTs significantly accelerate the crystallization process. Mechanical properties of the PET-SWNT nanocomposites improved as compared to neat PET indicating the effective reinforcement provided by nanotubes in the polymer matrix. Electrical conductivity measurements on the nanocomposite films showed that SWNTs at concentrations exceeding 1 wt% in the PET matrix result in electrical percolation. Comparison of crystallization, conductivity and transmission electron microscopy studies revealed that ultrasound assisted dissolution-evaporation method enables more effective dispersion of SWNTs in the PET matrix as compared to the melt compounding method.     

Extractive spectrophotometric determination of palladium using 2-(2-hydroxyimino-1-oxoethyl)furan

A rapid, simple, selective and sensitive method for the determination of palladium in trace amounts has been developed, based on the reaction of 2-(2-hydroxyimino-1-oxoethyl)furan [-isonitroso-2-acetyl-furan] with the metal ion in acetic acid. The intense yellow complex is quantitatively extractable into chloroform, whose absorbance is measured at 425 nm. The method is free from the interference of a large number of other metal ions. It obeys Beer's law in the range 0.0–3.8 g Pd mL^–1 with Sandell's sensitivity of 0.003 g Pd cm^–2. The ratios of metal to ligand in the extracted complex are 1:1 and 1:2. The analysis of various samples has been carried out with satisfactory and reproducible results.     

Palladium-catalyzed expedient Heck annulations in 1-bromo-1,5-dien-3-ols: Exceptional formation of fused bicycles

An unprecedented Pd-catalyzed intramolecular Heck cyclization has been investigated on halogenated diene scaffolds undergoing various mode of cyclization and termination leading to the formation of structurally differing fused cyclopenta(e)none and aromatic analogue. The discrimination in the fate of palladium intermediates formed in situ undergoing Heck cyclization preferentially arises out of the difference in reaction temperature as well as substrate architecture. Sequential Heck reaction of 1-Bromo-5-methyl-1-aryl-hexa-1,5-dien-3-ol derivatives followed by oxidation or termination via sp² CH activation in aromatic ring led to the formation of fused cyclopentanes. However, the similar reaction at elevated temperature showed predominance towards the formation of aromatic analogues via one pot cyclization and dehydroxylation. The mechanism for the formation of cyclopentanone fused with cyclopropane ring system is supported by density functional theory based calculations.     

Extractive spectrophotometric determination of niobium(V) with 3-hydroxy-2-(2-thienyl)-4H-chromen-4-one

A coloured complex of niobium (V) with 3-hydroxy-2-(2-thienyl)-4H-chromen-4-one (HTC) is produced in perchloric acid medium (4 mol/L); it is quite stable and extractable into dichloromethane. Beer's law is obeyed in the range 0.0–1.9 g Nb(V) mL^–1. The molar absorptivity at _max=420 nm is 5.0357×10⁴ L mol^–1 cm^–1. Using Job's method and the mole ratio method, the ratio of metal to ligand (Nb:HTC) in the extracted species has been found to be 1:2. The effect of anions and foreign metals is described.     

Buckling analysis of cylindrical thin-shells using strain gradient elasticity theory

The stability problem of cylindrical shells is addressed using higher-order continuum theories in a generalized framework. The length-scale effect which becomes prominent at microscale can be included in the continuum theory using gradient-based nonlocal theories such as the strain gradient elasticity theories. In this work, expressions for critical buckling stress under uniaxial compression are derived using an energy approach. The results are compared with the classical continuum theory, which can be obtained by setting the length-scale parameters to zero. A special case is obtained by setting two length scale parameters to zero. Thus, it is shown that both the couple stress theory and classical continuum theory forms a special case of the strain gradient theory. The effect of various parameters such as the shell-radius, shell-length, and length-scale parameters on the buckling stress are investigated. The dimensions and constants corresponding to that of a carbon nanotube, where the length-scale effect becomes prominent, is considered for this investigation.     

Performance model of metallic concentric tube recuperator with counter flow arrangement

A performance model for counter flow arrangement in concentric tube recuperator that can be used to utilize the waste heat in the temperature range of 900–1,400°C is presented. The arrangement consists of metallic tubular inner and outer concentric shell with a small annular gap between two concentric shells. Flue gases pass through the inner shell while air passes through the annular gap in the reverse direction (counter flow arrangement). The height of the recuperator is divided into elements and an energy balance is performed on each elemental height. Results give necessary information about surface, gas and air temperature distribution, and the influence of operating conditions on recuperator performance. The recuperative effectiveness is found to be increased with increasing inlet gas temperature and decreased with increasing fuel flow rate. The present model accounts for all heat transfer processes pertinent to a counterflow radiation recuperator and provide a valuable tool for performance considerations.