Substituent effects on cyclonona‐3,5,7‐trienylidenes: a quest for stable carbenes at density functional theory level

Nine boat‐shaped cyclonona‐3,5,7‐trienylidenes are compared and contrasted with respect to their multiplicity, nucleophilicity, electrophilicity, band gap (ΔE_{HOMO ? LUMO}), Natural bond orbital (NBO) atomic charge, force constant, as well as the aptitude for dimerization, and rearrangement through proper isodesmic reactions at B3LYP/AUG‐cc‐pVTZ and B3LYP/6‐311++G**//B3LYP/6‐31+G* levels of theory. The nine cyclic carbenes include unsubstituted (1_CH2) plus eight α‐cyclopropylcyclonona‐3,5,7‐trienylidenes, which are substituted with ?‐SiMe₂, ?‐NMe, ?‐PMe, ?‐O, ?‐S, ?‐CH₂, ?‐cyclopropyl, and ?‐CMe₂ (2_SiMe2, 2_NMe, 2_PMe, 2_O, 2_S, 2_CH2, 2_cyclopropyl, and 2_CMe2, respectively). The latter eight species enjoy the stabilizing interaction of the occupied Walsh orbital of cyclopropyl with the vacant p_π orbital of the carbene center (Walsh_cyclopropyl → p_{π carbene}). Among them, the singlet closed shell 2_NMe appears the most promising for exhibiting the highest relative singlet–triplet energy gap (ΔE_{s ? t} = 27.1 kcal mol^?1). In contrast, the least stable derivative is triplet 2_SiMe2, which exhibits the lowest relative ΔE_{s ? t} of ?5.5 kcal mol^?1. The overall trend of ΔE_s‐t is 2_NMe > 2_PMe > 2_S > 2_O > 2_cyclopropyl > 2_CMe2 > 2_CH2 > 1_CH2 > 2_SiMe2. With one negative force constant, the unsubstituted 1_CH2 turns out to be a transition state, whereas the rest emerge as minima. Copyright © 2015 John Wiley & Sons, Ltd.     

Three‐component One‐pot Synthetic Route to Functionalized N‐Phenyl‐ and N,N‐(1,4‐phenylene)‐2‐alkylimino‐2,3‐dihydrothiazoles under Mild,Solvent‐ and Catalyst‐free Conditions

A simple and efficient one‐pot synthesis of alkyl‐2‐(alkylimino)‐4‐methyl‐3‐phenyl‐2,3‐dihydrothiazole‐5‐carboxylate and dialkyl 3,3′‐(1,4‐phenylene)‐bis‐[2‐(alkylimino)‐4‐methyl‐2,3‐dihydrothiazole‐5‐carboxylate] derivatives from the reaction of phenylisothiocyanate (and also 1,4‐phenylene diisothiocyanate) and primary alkylamines in the presence of 2‐chloro‐1,3‐dicarbonyl compounds is described. This new protocol has several advantages such as lack of necessity of the catalyst and solvent, good yields,mild conditions and short times for reaction.     

The Synthesis of New Heterocycles Using 2‐(4‐Chloro‐1,3‐dihydro‐3,3,7‐trimethyl‐2H‐indol‐2‐ylidene) Propanedial

4‐Chloro‐2,3,3,7‐tetramethyl‐3H‐indole (an indolenine) was produced by the reaction of 5‐chloro‐2‐methylphenylhydrazine hydrochloride with 3‐methylbutan‐2‐one via Fischer reaction. Exposure of the indolenine to the Vilsmeier reagent at 50°C produced a β‐diformyl compound, 2‐(4‐chloro‐1,3‐dihydro‐3,3,7‐trimethyl‐2H‐indol‐2‐ylidene)propanedial. This dialdehyde was reacted with arylhydrazines, acetamidinium chloride, urea, thiourea, guanidinium chloride, and cyanoacetamide to give various 5‐membered and 6‐membered heterocyclic products, each carrying a 4‐chloro‐3,3,7‐trimethyl‐3H‐indol‐2‐yl unit as a substituent, in excellent yields.     

Graphite oxide: a simple and efficient solid acid catalyst for the ring-opening of epoxides by alcohols

A simple, efficient, and general procedure for the ring-opening of epoxides with various alcohols to give the corresponding β-alkoxy alcohols using graphite oxide (GO) as the catalyst, under very mild reaction conditions is described. The method proceeds in good to excellent yields and in short reaction times at room temperature under metal-free conditions.     

Remarkable regioselectivities in the course of the synthesis of two new Luotonin A derivatives

Ethyl 4-oxo-3,4-dihydroquinazoline-2-carboxylate reacts selectively with trimethylaluminium-activated 2-amino- or 4-aminobenzoic acid ethyl esters to give the corresponding anilides without self-condensation of the aminobenzoate building blocks. After propargylation, the quinazolinones were treated with Hendrickson's reagent, but only the para-substituted ester was found to undergo the expected [4 + 2] cycloaddition reaction, affording a new Luotonin A derivative. A different regioselectivity was observed with the ortho-substituted ester which affords a benzoxazinone under identical conditions. When the ester group in the ortho-substituted intermediate is replaced with a nitrile function, the outcome of the reaction with Hendrickson's reagent depends on the absence or presence of a base (DBU), yielding either a triphenylphosphonium-substituted iminobenzoxazine or a 4-cyano-substituted Luotonin A derivative.     

Unravelling the effect of temperature on viscosity-sensitive fluorescent molecular rotors

Viscosity and temperature variations in the microscopic world are of paramount importance for diffusion and reactions. Consequently, a plethora of fluorescent probes have evolved over the years to enable fluorescent imaging of both parameters in biological cells. However, the simultaneous effect of both temperature and viscosity on the photophysical behavior of fluorophores is rarely considered, yet unavoidable variations in temperature can lead to significant errors in the readout of viscosity and vice versa. Here we examine the effect of temperature on the photophysical behavior of three classes of viscosity-sensitive fluorophores termed ‘molecular rotors’. For each of the fluorophores we decouple the effect of temperature from the effect of viscosity. In the case of the conjugated porphyrin dimer, we demonstrate that, uniquely, simultaneous dual-mode lifetime and intensity measurements of this fluorophore can be used for measuring both viscosity and temperature concurrently.     

Electrochemical Properties of Ag@iron Oxide Nanocomposite for Application as Nitrate Sensor

Ag@iron oxide nanocomposite powders were synthesized via a two‐step chemical method. Characterization by UV‐Vis, XRD, SEM‐EDX and TEM revealed they are composed of nanosized crystalline silver particles in strict contact with amorphous iron oxide(s). The electrochemical behavior of the synthesized Ag@iron oxide composite was investigated by cyclic voltammetry. Compared with the single phase‐modified electrodes, the Ag@iron oxide/SPCE electrode exhibits an enhanced cathodic current in response to the target analyte, due to a synergistic effect between Ag crystallites and amorphous iron oxide nanoparticles. An amperometric sensor for detection of nitrate based on Ag@iron oxide modified screen‐printed electrode (Ag@iron oxide/SPCE) has been fabricated, showing a good sensitivity (663 µA mM^?1 cm^?2) and a detection limit of 30 µM.     

Effects of laser pulse wavelength and laser fluence on the characteristics of silver nanoparticle generated by laser ablation

Electrically pumped ultraviolet random lasing was achieved in metal-insulator-semiconductor (MIS) diodes based on ZnO films at room temperature. The ZnO films were grown by plasma assisted molecular beam epitaxy. Two different kinds of insulator layers, SiO _x (0<x≤2) and AlO _x (0<x≤1.5) were deposited by electron beam evaporation. X-ray diffraction experiments found these oxide layers were amorphous (or microcrystals), and X-ray photoelectron spectroscopy confirmed the Si and Al were fully oxidized. Compared with devices using SiO _x as the insulator layer, diodes with evaporated AlO _x layers showed a lower working threshold forward current (～20 mA to ～26 mA) and higher emission intensity. Periodic features indicating formation of closed-loop paths were deduced by the power Fourier transform of electroluminescence spectra. The cavity length of both devices increased as forward currents increased, while a larger cavity length was always obtained in the AlO _x -involved device under the same working current. The improved performance was attributed to larger hole amount in AlO _x layers. These results revealed that evaporated AlO _x can serve as good electron blocking and hole supplying layers for hetero-structures.     

The fractional q-differential transformation and its application

In this paper, the definitions and operations of the one-dimensional and two-dimensional fractional q-differential transform is proposed. A distinctive feature of the fractional q-differential transform is its ability to solve linear and nonlinear ordinary/partial fractional q-differential equations.     

Synthesis and characterization of novel dopamine-derivative:Application of modified multi-wall carbon nanotubes paste electrode for electrochemical investigation

Novel dopamine-derivative compound,3,5-diamino-N-(3,4-dihydroxyphenethyl)benzamide(3,5-DAB)was prepared in two steps.In the first step dopamine hydrochloride was reacted with 3,5-dinitrobenzoyl chloride in the presence of propylene oxide.In the second step reduction of nitro groups resulted in preparation of 3,5-DAB in quantitative yield.This material was characterized using conventional spectroscopic methods such as FT-IR and ~1H NMR.In addition,the redox response of a modified carbon nanotubes paste electrode of 3,5-DAB was investigated in aqueous solution at a neutral pH.The result showed that the electrode process has a quasi-reversible response,withΔE_p,greater than the(59/n) mV expected for a reversible system.Finally,the diffusion coefficient for redox process in paraffin oil matrix obtained using chronoamperometry methods.