Energy Profile Diagrams Research Articles

Photochemical Synthesis of 7,12-Dioxa[8]helicene and Density Functional Theory Studies: Unravelling the One-Way Valve System Involving Steric Crowding and Aromatic Stability.

C2 symmetric chiral 7,12-dioxa[8]helicenes were synthesized through a series of photochemical E-Z isomerization, electrocyclic reaction, and oxidation steps in a stepwise sequential manner at both the ends of 2,9-di((E)-styryl)naphtho[2,1-b:7,8-b']difuran. The chemical transformations complemented with density functional theory (DFT) studies delineate some fundamental concepts, exhibiting counter current effects, namely, destabilization caused by increasing steric crowding and stabilization caused by aromatic units on the overall transformation. The calculated energy profile diagram unravels the formation of photoinduced intermediate species with increasing free energies for the E-Z isomerization and the electrocyclic reactions; the reverse processes for the said steps are prevented by a specific barrier-less oxidation step forming aromatic rings, presenting a one-way valve situation. The steric crowding-related increase in free energy and its counterbalancing by aromaticity have been illustrated for the helicene system using DFT studies. HOMA analysis shows that each individual ring in 7,12-dioxa[8]helicene exhibits a strong aromatic character, supporting the Fries model empirically. Interestingly, despite the nonplanar and sterically crowded geometry, 7,12-dioxa[8]helicene displayed a large HOMO-LUMO gap, typical of aromatic compounds.

Highly efficient oxidative C–H/C–H cross coupling of xanthines over bimetallic Ni/Ag@titania: The key role of surface polymorphism and mechanism by surface-enhanced Raman scattering

A new effiecient protocol for the cross dehydrogenative coupling (CDC) of C8(sp2)-H/C(sp2)-H of xanthines and aromatic compounds over nanosized bimetallic Ni/Ag@titania catalyst is presented. The notable properties of Ni/Ag bimetallic nanoparticles (NPs) facilitate the 2-fold activation of classically inert C(sp2)-H bonds. Molecular level study for the catalyst efficiency was determined, by performing the model reaction between caffeine and vanillin, on different catalysts, synthesised by varying the loading of two component metals, on four polymorphic forms of titania, brookite, rutile, anatase and mesoporous. Among the 63 catalyst systems, 5:1 Ni/Ag@anatase showed excellent catalytic activity in dry DMSO with 88% product formation. Tert-butyl hydroperoxide (TBHP) and H2O2 were used as oxidant. The regioselectivity of the CDC reaction depends on the nature of peroxide used. Non-covalent surface π-stacking interaction occurring between peroxide modified titania (PMT) and aromatic ring(s) is the key for the observed regioselectivity. Catalysts were characterised by UV–Vis, FT-IR, powder XRD, XPS, SEM, TEM, etc. The catalytic system showed good operational stability, functional group tolerance, robustness and recyclability. We identified the intermediate(s) through real time monitoring of SERS and proposed the most plausible catalytic cycle as well. Further, a possible energy profile diagram involving the transition states was obtained computationally by DFTB calculations. Almost all the products were afforded in good to excellent yields. Thus, the present process constitutes one straightforward and clean approach to a class of much sought organic transformation.

Deciphering the sensing mechanism in a sarin gas surrogate, diethylchlorophosphate specific probe: Colorimetric observation and theoretical analysis

The extreme toxicity of organophosphates (OPs) nerve agents poses a significant public health risk and national safety. Increasing interest in developing reliable and accurate methods for simple and fast detection of these toxic, i.e., poisonous chemicals, is necessary and urgent. In this contribution, [(E)-3-(4-(dimethylamino)phenyl)allylidene)amino)phenol] (DPAP), a cinnamalimine-based chromogenic probe with high selectivity and sensitivity towards the detection of sarin mimic diethylchlorophosphate (DCP), has been introduced. The detection limit of DPAP towards the detection of DCP is in the nM region. The developed probe DPAP shows reddish pink color upon treatment with DCP and reverses to its original one by adding triethylamine (TEA); it is observed eight times reversibility by alternative addition of DCP and TEA. The detailed mechanism has been elucidated through the density functional theoretical analysis depicting the energy profile diagram and Frontier molecular orbital analysis. To establish the practical application, we have demonstrated a paper strips-based test kit to establish the capacity of DPAP for on-spot detection and quantification of DCP. A dip-stick experiment has also been performed to identify DCP in the gaseous phase within the various OPs, inorganic phosphates, and other toxic analytes to establish the probe, DPAP, as a proficient chemosensor. To detect the response capacity of probe DPAP towards the identification and quantification of DCP, a time-dependent UV–visible spectrophotometric experiment, and dip-stick method have been performed for 0–6 min. A smartphone-based readout technique has been executed for on-spot detection and quantification of DCP in remote areas. The present contribution introduced an excellent probe and technique for identifying and quantifying sarin gas in actual threatening situations. It would be helpful to monitor the environmental toxicology from exposure to these toxic nerve agents.

Unexpected formation of 2-methyl-1H-naphtho [2, 3-d] imidazole via decarboxylation governed mechanistic pathway

Present work is the outcome of the synthetic strategy for the naphthalene analogue of benzimidazole dimer, 2-methyl-1H-naphtho [2, 3-d] imidazole. It was found that 1H-naphtho [2, 3-d] imidazol-2-yl) methane (2b') was formed instead of respective dimer. Herein, we have reported two synthetic ways for 2b', first conventional refluxing method with 70 % yield and second by using synthesis reactor with 75 % yield. Both the way of synthesis involves the reaction of 2,3- diamino naphthalene and diethyl malonate in acidic medium. This example belongs to C-2(sp2)-C-1(sp3) type decarboxylation. To the best of our knowledge, it is the first-time synthesis of the 2b‘ has been reported via decarboxylation pathway along with crystal structure and DFT studies. Most probable mechanisms for both the compounds have been proposed based on the energy profile diagram and thermodynamic data obtained by DFT calculations [B3LYP/6-311++G (d,p)] in gas phase. Absorption responses showed potential of the naphthaimidazole based molecule 2b‘ as a pH and metal ion sensor of various hazardous metals such as As3+, Cr3+, Hg2+,Cd2+, Pb2+.

Low-velocity single and repeated impact behavior of 3D printed honeycomb cellular panels

Abstract In this study, low velocity single and repeated impact behaviors of 3D printed curved honeycomb cellular panels that can be used for impact protection are investigated. The energy absorbing capacity of the 3D printed honeycomb curved panels is predicted by evaluating the results. In addition, the changes in the fundamental free vibration frequencies of the panels subjected to impact are examined to have an idea about the presence of the damage. The effect of curvature on the damage mechanisms of 3D printed honeycomb panels is studied by examining the contact force–deformation curves, energy profile diagrams, and SEM images. The experimental results indicate that the radius of curvature of the cellular panels highly affects the impact and free vibration behavior, and the change in the natural frequency due to the impact damage is more considerable for ABS than PLA.

Rate constant and mechanism of the OH-initiated degradation of 3-penten-2-one in the atmosphere

A systematic investigation has been performed on OH-initiated atmospheric oxidation mechanism of 3-penten-2-one (3P2) using a high-level ab initio method. The energy profile diagram information is obtained at the CCSD(T)/6-311++G(d,p)//BH&HLYP/6-311++G(d,p) + 0.9335 × ZPE levels of theory. The calculated total rate constant at 298 K using the transition state theory with tunneling corrections is found to be 3.28 × 10−11 cm3 molecule−1 s−1, which is in reasonable agreement with the experimental determination. The temperature-dependent rate constant for the reaction of 3P2 with OH radicals from 200 to 1000 K is predicted to be k = 4.44 × 10−24 × T3.9 × exp(2177/T) cm3 molecule−1 s−1. Based on mechanistic studies, our results show that acetaldehyde [CH3C(O)H], methyl glyoxal [CH3C(O)C(O)H], 2-hydroxypropanal[CH3CHOHC(O)H], peroxyacetyl nitrate CH3C(O)OONO2 (PAN), CO2, formaldehyde [HC(O)H], and CH3C(O)CHOHC(O)CH3 are the predominant products for the 3P2 + OH reaction under atmospheric conditions, which agrees closely with the experimental findings.

Revisited the mechanism of cobalt(III) catalyzed cyanation of arenes and heteroarenes: A DFT study

Transition metal catalyzed cyanation of arenes and heteroarenes by CH activation is an attractive process for functionalization of aromatic system. One such reaction under the catalysis of cobalt complex using N-cyano-N-phenyl-p-toluenesulfonamide as a cyanating reagent was studied theoretically. Metal mediated cyanation of aromatic ring involving one and more acetic acid have been explored. Our finding reveals that during the metal mediated activation of CH bond, presence of two acetic acid, increase the activation energy of the proton abstraction step. Comparison of the energy profile diagrams for single and double acetic acid mediated steps shows that the pathway, assisted by single acetic acid, is energetically more favorable. The calculated apparent activation barrier of the reaction is also consistent with the experimental report and it also shows high temperature (120 °C) has been needed to carry out the reaction.

Pd(II) complexes with ONN pincer ligand: Tailored synthesis, characterization, DFT, and catalytic activity toward the Suzuki-Miyaura reaction

A pincer type ONN tridentate Schiff base ligand, 2-(((pyridin-2-yl)methylimino)methyl)-6-methoxyphenol, (L1) synthesized by the condensation of 4-hydroxy-3-methoxy-benzaldehyde and (pyridin-2-yl)methanamine. The ligand L1 and the new Pd(II) heteroleptic complexes of the composition [Pd(L1)(L2)]Cl, where L2 = benzimidazole, imidazole, benzooxazol or pyridine were synthesized and characterized by a set of chemical, spectrometric and spectroscopic analyses. These complexes were named 1 to 4, respectively. The FT-IR and DFT have suggested that ligand is coordinated with metal through azomethine-N and phenolic-O and arranged in square planar fashion around the metal. Correlation coefficients value between 0.995 - 0.993 shows satisfactory agreement in theoretical and experimental 1H-NMR and 13C-NMR. Benzimidazole anchored complex 1 exhibits an excellent catalytic activity. DFT calculated the energy profile diagram of the Suzuki-Miyaura reaction.

Atmospheric impact of Z- and E-isomers of CF3CH[dbnd]CHC2F5 molecule initiated by OH radicals: Reaction mechanisms, kinetics and global warming potential

In this manuscript, we have explored the reaction mechanism, kinetics and global warming potentials of Z- and E-isomers of CF3CHCHC2F5 molecule initiated by OH radical to understand its impact on the atmospheric environment. Energy profile diagram for OH-initiated reaction pathways for these two isomers are constructed from the data obtained at M06-2X meta hybrid density functional theory along with aug-cc-pVTZ basis set. The observed potential energy and enthalpy and Gibb's free energy of the reactions suggest that OH-addition to Z- and E-isomers is more feasible than the hydrogen abstraction reactions. The rate coefficients of each reaction channel are evaluated by using conventional transition state theory within the temperature range of 200–350 K. We found that the overall rate coefficient for Z-isomers decreases with the increasing temperature, whereas this value increases for E-isomer with the increasing temperature. The overall rate coefficients for both isomers (Z and E) are fitted to modified Arrhenius three parameters and expressed as koverall(Z) = 9.06 × 10−21 T2.20 exp (1054.89 ± 0.93/T) and koverall(E) = 1.09 × 10−21 T2.77exp (394.40 ± 1.52/T) cm3 molecule−1 s−1 respectively. The calculated rate coefficients and branching ratios for each reaction channels indicate that OH radical addition to unsaturated carbons of Z/E- CF3CHCHC2F5 molecules are more dominate to the overall reaction than H-abstraction reactions. Finally, we have estimated atmospheric lifetimes and GWPs of Z- and E-isomers of CF3CHCHC2F5 molecule.

Survey for Transition of Normal Reaction

Transition of reaction is a short-lived unstable molecule in a reaction which is formed in between the reaction when reactants change into products. Whereas, transition state is just the state before formation of new molecule (involves breaking of bonds of reactants and formation of new ones) Transition of reaction differs from a transition state in that the intermediate has a discrete lifetime (be it a few nanoseconds or many days), whereas a transition state lasts for just one bond vibration cycle. Intermediates may be unstable molecules (in which case they are called reactive intermediates) or highly stable molecules. The difference between them can be better described through the energy profile diagram.

Analysis of impact energy absorption by lightweight aramid structures

This paper presents and analyses the behaviour of aramid composite plates subjected to low and medium impact energies. In order to study the material behaviour under impact loading, experimental tests have been performed using a drop-weight tower and a pneumatic gas gun within the range of impact energies (20J<Eimp<600J). The plates are impacted by hemispherical impactor and spherical projectile for drop-weight and impact tests, respectively. The influence of areal density is also evaluated in terms of absorption energy. Energy Profile Diagrams (EPD) are used to identify the penetration and perforation thresholds enabling the definition of the no-penetration, penetration and perforation zones. The results revealed that there is a greater energy absorption capacity in thin plate than in thick plate for low impact energy values. However, areal density is relevant in the energy absorption capacity for high impact energy values.

Single and repeated impact behaviors of bio-sandwich structures consisting of thermoplastic face sheets and different balsa core thicknesses

Abstract This paper aims to investigate the single and repeated impact behaviors of bio-sandwich structures consisting of E-glass fiber – reinforced thermoplastic face sheets and balsa cores. Low velocity impact tests were performed using a drop-weight impact machine under a hemispherical impactor. Preliminary single low velocity impact loadings were applied to the bio-sandwich composites with different core thicknesses (namely 15 and 25 mm) so as to obtain the energy limits which were ranged from fully elastic level (10 J) to perforation energy level (80 J). Impact behaviors and damage mechanisms which occurred at both face sheets and internal parts of the balsa core were elucidated through the energy profile diagrams and force – deformation (F-D) curves under low velocity single impact loadings. Besides, low velocity repeated impact tests of the bio-sandwich structures were performed with the same impact energy levels. Repetitive impact behaviors were also investigated with F-D curves at some specific repeated impact numbers. Impact failures which occurred in the upside and bottom of composite structures were detected with digital camera. According to the experimental findings, it was concluded that the total number of impact loads under impact energy level of 10 J until perforation were 38 for the sandwich structures with 15 mm balsa core thickness while it was 98 for the sandwich structures with 25 mm balsa core thickness. Based upon the test results, the number of impacts for perforation (Nr) under smaller impact energies without testing was easily predicted with the derived equation in the form of E i = a N r b , where Ei represents the impact energy while a and b are the constants.

Synthesis of AgWCNx Nanocomposites for the One-Step Conversion of Cyclohexene to Adipic Acid and Its Mechanistic Studies.

A novel catalyst composed of silver nanoparticles grafted on WCNx has been prepared by using a facile pH-adjusted method. The material reported in this study presents a non-mineral acid route for the synthesis of the industrially significant monomer adipic acid through the selective oxidation of cyclohexene. Ag has been stabilized in the hydrophobic matrix during the formation of the mesoporous silica material by using aniline as stabilizing agent. A cyclohexene conversion of 92.2 % with 96.2 % selectivity for adipic acid was observed with the AgWCNx -2 catalyst, therefore, the AgWCNx catalyst was found to be efficient for the direct conversion to adipic acid with respect to their monometallic counterparts. The energy profile diagrams for each reaction path by using the AgWCNx catalyst were studied along with their monometallic counterparts by using the Gaussian 09 package. The reported material can avoid the use of harmful phase-transfer catalysts (PTC) and/or chlorinated additives, which are two among other benefits of the reported work.

Dynamic properties of carbon nanotubes reinforced carbon fibers/epoxy textile composites under low velocity impact

Abstract In this study, the impact response of polymer composites containing a random distribution of carbon nanotubes (CNTs) has been investigated by considering energy profile diagrams and associated force-time curves. The composite consists of CNTs initially filled Epon 862 Epoxy resin and implanted between plies of T300 6k Carbon fiber with 5HS (satin) weave. Different mass fractions of CNTs were used: 0% as reference, 0.5%, 1%, 2% and 4%. Taylor impact test was used to obtain the impact response of specimens. Projectile manufactured from a high strength and hardened steel with a diameter of 20 mm and 1.5 kg of mass was launched by a compressed gas gun within the velocity of 7 m/s. Deformation histories and damage modes of specimens were recorded during impact using high-speed camera. The effect of CNTs amount on dynamic properties and damage process was discussed.

Hydrogen atom abstraction from Piperazine by hydroxyl radical: a theoretical investigation

ABSTRACTDual level of quantum mechanical calculations have been carried out for hydrogen abstraction from Piperazine [HN(CH2CH2)2NH] initiated by OH radical. Geometry optimisation and frequency calculations of all species involved in the titled reaction have been performed at M06-2X/6-31+G(d,p) level of theory. For the accuracy in the thermochemistry and kinetics data, single-point energy calculations have been further carried out at coupled cluster CCSD(T) method along with 6-311G(d,p) basis set. An energy profile diagram for the reaction has been plotted along with pre-reactive and post-reactive complexes at entrance and exit channels. Intrinsic reaction coordinates (IRCs) calculations have been performed for identification of real transition states that connect it via reactant to product. Our result shows that the H-atom abstraction takes place from the C–H position of Piperazine. The rate constant is calculated using canonical transition state theory (CTST) is found to be 2.86 × 10−10 cm3 molecule−1 s−1 which is in good agreement with the reported experimental rate constant (2.38 ± 0.28) × 10−10 cm3 molecule−1 s−1 at 298 K. We have also reported rate constant for the temperature range 300–500 K. Using group-balance isodesmic reaction, the standard enthalpies of formation for Piperazine and product radicals generated by hydrogen abstraction are reported. The branching ratios for both reaction channel (i.e. H-abstraction from –CH2 and –NH position of Piperazine) are found to be 93% and 7%, respectively. The calculated atmospheric life time of Piperazine is found to be 0.97 hour.

Non-destructive evaluation of damage modes in nanocomposite foam-core sandwich panel subjected to low-velocity impact

Abstract This research studied the effect of multi-walled carbon nanotubes (MWCNTs) on the internal and external damages of foam-core sandwich panels with kevlar fiber reinforced epoxy face sheets subjected to a low-velocity impact. The sandwich panels were subjected to six levels of energy. Energy profile diagrams (EPDs) were plotted to determine the rebounding, penetration and perforation thresholds of the sandwich panels. Non-destructive evaluation methods have been employed for detecting and measuring damage size of the sandwich panels using X-ray radiography and active infrared thermography. The results show that MWCNTs can improve the absorbed energy and penetration threshold of the foam-core sandwich panels.

Catalytic Hydrogenation of CO2 by Manganese Complexes: Role of π-Acceptor Ligands

We have carried out computational studies on the CO2 hydrogenation reaction catalyzed by three different Mn-based complexes (Mn1, Mn2, and Mn3) to understand the role of σ-donor (PMe3) and π-acceptor (CO) character of the ligands. Further, the role of a different set of σ-donor and π-acceptor ligands is studied as the studied CO (π-acceptor and PMe3 (σ-donor) ligands have the differences not only in electronic properties but also in steric effects. Here, we find that the σ-donor ligands (PMe3/PH3) favor the hydride transfer, whereas the π-acceptor ligands (CO/PF3) favor the heterolytic H2-cleavege. The energy profile diagram shows that the hydride transfer is the rate-determining step when the CO2 hydrogenation reaction is catalyzed by a Mn-complex containing σ-donor (PMe3/PH3) and π-acceptor (CO/PF3) ligands.

Thickness-dependent energy dissipation characteristics of laminated composites subjected to low velocity impact

This study investigates the low velocity impact properties such as damage thresholds, critical energy thresholds and damage process of laminated composites. Damage thresholds of Hertzian failure and main failure corresponding to woven and unidirectional Glass Fiber Reinforced Polymer laminates in varying thicknesses from 2mm to 8mm are determined through impact tests with nominal impact energies of 4, 6, and 8J/layer. Hertzian failure and main failure thresholds of a composite laminate with a particular thickness remain substantially constant with the nominal and incipient impact energies. Energy profile and normalized energy profile diagrams are used to find out the penetration and perforation thresholds as well as explaining the correlation between the threshold energies and damage process of the laminates. Dissipated energy by a laminate is determined using a second order polynomial regression based on the relationship between energy dissipation and impact energy of data points before penetration. Penetration and perforation energies increase non-linearly with the thickness and thickness dependence is expressed using a power regression. Test results related to damage thresholds, threshold energies and effective damage area reveal that unidirectional laminates possess lower impact damage resistance and hence are more sensitive to impact damage.

Impact responses and residual flexural properties of narrow CFRP laminates

This study aims to identify the impact responses and residual flexural properties of narrow carbon fiber reinforced plastic (CFRP) laminates using the energy profile diagram (EPD). A serial of impact tests was performed with different thicknesses of narrow CFRP laminates to examine the damage process and extent from initiation to complete breakage. The quasi-static three-point bending tests were carried out to characterize the degradation of residual flexural properties induced by the impact. The overall impact energies are clearly separated into three regions by the penetration threshold and crack threshold respectively determined by the EPD. The main damage modes are matrix cracking for lower impact energies, delamination and fiber breakage for middle impact energies and complete breakage for higher impact energies. It is also found that the degradation of normalized residual flexural properties can be divided into three regions using these abovementioned two thresholds, of which the greatest loss occurs in the middle energy region, whilst the maximum reductions of normalized flexural strength and flexural modulus are smaller than 20% in the first region. By comparison, the 6-ply specimens are of lower impact resistance and lower residual flexural properties than the 9-ply specimens under same impact energy; and the residual flexural strength is more sensitive to impact loading than flexural modulus.

Low-velocity impact response of woven Kevlar/epoxy laminated composites reinforced with multi-walled carbon nanotubes at ambient and low temperatures

In this article, the low-velocity impact response of woven Kevlar/epoxy laminated composites enhanced with different weight percentages (⩽1%) of multi-walled carbon nanotubes (MWCNTs), was investigated under ambient (27°C) and low temperature (−40°C) conditions. Energy profile diagrams (EPDs) were employed to determine the penetration threshold of Kevlar/epoxy laminated composites. In addition, the effect of MWCNTs on laminate composites was evaluated by subjecting all specimens to the same level of energy, 45J. The time history of absorbed energy, deflection and velocity are measured and some parameters such as stiffness bending, penetration limit and maximum deflection, for both composites and nanocomposites at ambient and low temperatures are reported. Results showed a remarkable dependency of damage formation on temperature and contents of MWCNTs. It was concluded that the MWCNTs was improved the impact response and was restricted the damage size in the woven Kevlar fiber composites at ambient and low temperature. The addition of 0.5% MWCNTs resulted in about 35% increase in energy absorption at ambient temperature, and the addition of 0.3% MWCNTs increased the absorbed energy capability about 34% at low temperature.