Theory and Applications of Chemistry Vol. 2

Semiconducting Oligomers of 1,4-dimethoxybenzene, Thiophene and Thiazole: A Theoretical Study

2021-07-26T09:13:25+00:00

Organic semiconducting oligomers containing three to nine heterocyclic units and based on 1,4-dimethoxybenzene, thiophene and thiazole have been studied by DFT and TDDFT at the B3LYP/6-31G(d,p) level. The energy of each molecule, those of the frontier orbitals HOMO and LUMO, the width of the band gaps and the optical properties have been calculated. The inter-ring distances, dihedral angles and torsional angles have been elucidated. These molecules are planar π-conjugated systems. The band gaps of the longer oligomers studied range from 2.53 to 2.72 eV and their excitation energies calculated by TDDFT vary from 2.22 to 2.36 eV. Wavelengths of absorption bands of 524 to 556 nm are also obtained by TDDFT. The results of this theoretical study show that these organic molecules have interesting properties and can potentially be used as components in solar cells. In this work, a theoretical investigation on the geometries and optoelectronic properties of oligomers based on 1,4-dimethoxybenzene, thiophene and thiazole has been done. Molecules that contain up to nine rings have been studied. For all these oligomers, the elongation of the molecular chain led to a gradual decrease of the energy gap between the frontier orbitals. This energy splitting varied from 2.5 to 3.7 eV. This indicates that these compounds may exhibit semi-conducting properties. The increase in the molecular chain length also induced a decrease in the excitation energy determined by TDDFT. These oligomers present many intra and inter-unit interactions which contribute to their rigidity and to a better delocalization of the π-electrons.

Superluminal Hydrogen Atom in a Constant Magnetic Field in (3+1)-dimensional Spacetime (II)

2021-07-26T09:17:20+00:00

As has usually been the case in the tradition of some scientiﬁc novel ideas, we use the hydrogen atom as a “test particle”, in the context of superluminal dynamical system theory. In Paper (I) of this series, the fundamental effect of an applied external magnetic ﬁeld on a transversely guided beam of hydrogen-like atoms is uncovered, that of transformation from spherical wave expansion into plane wave function. This leads to an unprecedented concept of a planar helical hydrogen ﬁeld, with a continuum of linear momentum in (3+1)-dimensional spacetime. Thereupon, we investigate a possible “superluminality” of this ﬁeld. It turns out that, as in the case of a free Dirac ﬁeld, the Dirac-hydrogen ﬁeld accords with the law of conservation of energy and momentum. As a result, the generalized translational velocity component expectation value of the planar Dirac-hydrogen is found to exceed the speed of light, with however, a subluminal minimal velocity.

Economic Design of OTEC Power Plant with Concurrent Production of Desalinated Water – A Case Study

2021-07-26T09:21:29+00:00

Ocean Thermal Energy Conversion (OTEC) power plants offer a green source of renewable energy. Since India is a tropical country and a peninsula, the prospects of OTEC power generation are extremely bright in India. Among the three modes of operation (open cycle, closed cycle and hybrid cycle) of OTEC system, the hybrid mode is most promising. However, one of the chief technical obstacles in OTEC power plant design is that since the temperature difference driving force available is of the order of 10-15ºC only, the size of the heat exchanger (evaporator / condenser) required becomes exorbitantly large. The use of variable area design, developed by the author and his co-workers, has been recommended in this connection. Such a design provides substantial increase in heat transfer coefficient (350 to 450% increase) with insignificant increase in the associated pressure drop penalty (118 to 120% increase). The required size of the heat exchangers thus gets reduced tremendously, while the operating cost does not increase materially, thereby making design and operation of OTEC power plants economical and cost- effective. The performance characteristics of such heat exchangers (Variable Area Heat Exchangers or VAEs) are discussed in detail in this paper. Further, in the hybrid mode of operation of OTEC system, low pressure steam is produced by the flash evaporation of sea water and this steam is used as heating fluid in the evaporator (of variable area design) to evaporate the working fluid (ammonia, freon). The condensate from this exchanger thus forms desalinated water, which constitutes a valuable by-product of the process. Apart from generating clean electric power around the clock (without consuming any valuable raw material), this power plant thus produces several gallons of desalinated water also per day.

Cu4SnS4 Thin Films: Advances in Research

2021-07-26T09:28:15+00:00

Cu₄SnS₄ thin films have been synthesized using electro deposition, chemical bath deposition and Thermal evaporation method. XRD confirmed that these films have polycrystalline in nature with orthorhombic structure. The band gap was determined using UV-Visible spectrophotometry data, about 1.2 to 1.94 eV. The obtained films could be used in solar cell application due to appropriate band gap and good photo response behavior.

Pericyclic Reactions vs Polar Reactions. Use of Heterocycles as Electrophiles. Microwave Irradiation

2021-07-26T09:33:17+00:00

Considering the possibility of analyzing polar cycloaddition reactions, in this work we studied a series Diels-Alder reaction using different heterocycles derivatives acting as electrophiles joint to dienes of different nucleophilicity, analyzing the effect of the microwave irradiation in these processes. For this, two reaction conditions have been worked: toluene as solvent and solvent free. The last one presents the better yield in shorter time of reaction. Using microwave heating the aromatic cycloadducts are clearly predominant. The reactions that will be discussed could be considered of the pericyclic type, however taken account the effect of the solvent on them, they could also be considered polar. Consequently, it would be in the presence of a borderline situation. The methodology explored could be used in commercial form. However, it would be necessary to have the required equipment for this purpose. From a formal point of view the reactions that are discussed could be considered polar. Considering the dynamics of the reactions, in only one case it was possible to verify the presence of an intermediate state, while in the rest of them there was observed the presence of concerted and markedly asynchronic reactions. For all these reasons in this work we try to discuss the scope of this reactive model and its location in the panorama of the ways in which it proceeds according to the reaction mechanism. That to say if for this kind of process, the concept of pseudo-pericyclic reaction is applicable. The important solvent effect observed in these persuades us to consider these processes as PD-A reactions in which an electrophile reacts with a nucleophile. On the other hand, when microwave irradiation was used, the best results were obtained in free solvent conditions. We confirm this approach using theoretical calculations based on Density Functional Theory (DFT).

Use of the Arrhenius Equation in Kinetic Analyses and Mathematical Modeling of Rate Data Requires the Most Precise, Even Scrupulous, Application and Term Definitions

2021-07-26T09:36:17+00:00

This article presents a critical analysis of the frequent practice of using the Arrhenius equation for mathematical modeling of very many physical and chemical rate processes. This approach may also be used to characterize the controls and mechanisms of the rate processes investigated. We also discuss the specific form of the Arrhenius-type equation as a relationship meriting detailed investigations. In our opinion, the use of the Arrhenius relationship often can only approximate to the behavior of such systems, exemplified by the systems discussed below, including the work of N N Semenov, A K Galwey, A G Mershanov, etc. We draw attention to "erroneous" experimental designs, including the so-called "global kinetic mechanism" and other widespread uses of theoretical models which do not necessarily represent the real situation. Such limitations in rate data analyses impact negatively throughout this branch of science. Here we attempt to question these accepted practices realistically and find answers to the types of studies under consideration that do not include the misconceptions often contained (concealed) therein. Unfortunately, besides the scientific component, various political and social applications often interfere in the process by introducing errors. This symbiosis of delusions is considered for the example of “solid flame”, a Russian theme that may not be familiar to English-speaking readers. The consequences of repression for scientists in connection with their position on scientific issues are described.

Preparation of Bisoprolol Impurity A of High Quality

2021-07-26T09:40:46+00:00

Aims: Research on the convenient method for obtaining (RS)-1-(4-Hydroxymethyl-phenoxy)-
3-isopropylaminopropan-2-ol, known as the Impurity A of Bisoprolol according to EP, of high quality. Study Design: Impurity A may be formed as a by-product in the common processes used for synthesis of bisoprolol fumarate. Impurity A may be also formed as a result of degradation (hydrolysis) of Bisoprolol. This chemical compound is available as the reference standard, but the offered purity is between 95% and 97%, what suggest that its purification to high quality is demanding. The most common method used for purification of chemical standards is preparative chromatography, but it is unattainable in many cases. There is continuous need for simple, convenient and repeatable laboratory procedures.

Methodology: The synthesis of Bisoprolol Impurity A was performed starting from
p-hydroxybenzyl alcohol and subsequent reactions with epichlorohydrin and isopropylamine. Purification process consisted particularly on obtaining and isolation of fumarate salt of Impurity A, its crystallization and subsequent basification.

Results: The reference standard of Bisoprolol Impurity A of 95.5% purity was obtained with convenient purification process. The structure of Impurity A was elucidated with IR, NMR and EA and its purity was determined by HPLC technique.

Conclusion: The effective method of preparation of Impurity A of high quality is described in this paper.

Speciation of Some Heavy Metals in Sediments of the Pennington River, Bayelsa State, Nigeria

2021-07-26T09:45:23+00:00

Speciation helps in the identifications and quantification of the defined geochemical fractions, forms or phases in which an element exists in the environment. Speciation in sediment compartment is a significant step to understand the potential environmental risk, distribution, mobility and bioavailability of pollutants. The total heavy metal concentrations of some environmentally toxic metals in sediments of the Pennington River System, Bayelsa state, Nigeria was examined. The concentrations of heavy metals in each fraction were determined using a ANALYST 400 Perkin-Elmer AAS. The mean concentrations (mg/kg) for the six metals in dry season sediment samples were: 0.14±0.17(As), 0.39±0.55(Co), 2.43±5.06(Cu), 26.82±22.19(Fe), 0.69±1.10(Pb), and 1.22±1.19(Zn), while the mean metal concentrations (mg/kg) in wet season samples were:0.11±0.18(As),0.37±0.6(Co), 2.07±4.35(Cu), 26.65±24.79(Fe), 0.61±1.08(Pb), and 1.11±1.00(Zn) respectively. Speciation study applying the five-stage sequential extraction scheme revealed that As, Co, and Pb in sediment prevails mostly in exchangeable fraction. Cu and Zn were more prevalent in residual fraction, while Fe was found more in residual and Fe/Mn-Oxide fractions. In an attempt to infer anthropogenic input from natural input, comparison with sediment quality guideline (SQGs) and ecotoxicological sense of heavy metal contamination was employed. The concentration of the studied heavy metals in Pennington River System does not pose a threat to the sediment dwelling fauna and anyone who consumes aquatic animals, particularly fish, from the Pennington River. According to SQGs, the studied heavy metals of the Pennington River sediments were under the category of non-polluted. Speciation is a powerful and versatile technique for predicting the degree of contamination risk of a river system. In this present study, all heavy metals investigated are relatively stable under normal conditions of Pennington River system. This means that there is a low source of pollution arriving to the Pennington River system. Iron was found to be the highest occurring heavy metal and arsenic was the least occurring heavy metal in this study. Furthermore, there is no heavy metal pollution threat pose to sediments dwelling fauna and anyone who consume aquatic animals, particularly fish from the Pennington River system. To preserve the unpolluted state of the Pennington River system it remains important that allochthonous inputs are devoid of heavy metals.

A Comparative Study of Two Different Media Effect on the Electropolymerization of 2-(9-ethylcarbazol-3-yliminomethyl)phenol by Cyclic Voltammetry, Impedance Spectroscopy, XPS, UV-visible Measurements and DFT Calculation

2021-07-26T09:51:06+00:00

A carbazole-based monomer, 2-(9-ethylcarbazol-3-yliminomethyl)phenol (SIC), was first synthesized and characterized. It was afterward polymerized by potentiostatic methods. Oxidative polymerization of SIC was carried out in two media. The first one (i.e. Bu₄NBF₄ (0.1M)/MeCN) gives the poly(2-(9-ethylcarbazol-3-yliminomethyl)phenol). However, the second one (LiClO₄/MeCN + 35mM HClO₄), leads to another polymer, the poly(2-(9-ethylcarbazol-3-yliminomethyl)cyclohexa-2,5-diene-1,4-dione).These two novel polymers will be abbreviated here after as PSIC and PDIC, respectively. If the formation of PSIC was expected, the formation of PDIC in acidic medium isn’t. It was explained by a hydroxyl function oxidation of SIC. The obtained polymers were then characterized by cyclic voltammetry, electrochemical impedance spectroscopy, XPS, IR and UV-Vis spectroscopies. Furthermore, the corresponding electrochemical and optical bandgap values were calculated in order to get an idea about the conductive properties. The related results show that PDIC and PSIC are good conductive polymers. The electrochemical polymerisation of SIC is performed in both protic and organic medium. During the anodic oxidation in protic medium containing LiClO₄/MeCN + (35mM) HClO₄, SIC undergoes hydrolysis around 1V, which modifies its structure before its polymerization. This reaction is very fast, and leads to the formation of two isomers, para-quinone and ortho-quinone (DIC) which oxidizes at the same potential and form PDIC. In the organic medium, the SIC retains its initial structure, and leads after oxidation to the corresponding polymer PSIC. The electrochemical behaviour of PSIC and PDIC supports the conductive character of both polymers and the difference between their structures. In an acidic medium, the imine bond undergoes a protonation which increases commonly the planarity of the polymeric material and subsequently, improves its electrical properties. The charge transfer resistance recorded for the PDIC film was much lower than the one recorded for the PSIC film. The electrochemical and the optical bandgaps of PDIC are lower than those of PSIC. The difference in structures of both polymers could explain these results. Compared to SIC, para-quinone and ortho-quinone compounds are formally electrons donor-acceptor (D-A) type moieties. In a D-A system, a charge transfer from the donor to the acceptor increases conjugation length through resonance which causes the decrease of its bandgap. Therefore, these findings indicate that PDIC is more conductive than PSIC.

Analysis of Properties of Biolubricant Obtained from Blends of Used Palm Oil

2021-07-26T09:57:25+00:00

Vegetable oils are providing alternatives as renewable sources for the production of ecofriendly biolubricants due to increasing environmental challenges, depleting mineral energy reserves, and cost of production from fossil sources. This study evaluates the quality parameters of biolubricant obtained from used palm oil (UPO). The crude UPO was filtered, centrifuged at 500 rpm, and dried over Na₂SO₄ crystals overnight. The quality parameters of the pretreated UPO (PUPO) were analysed to authenticate its potential for the production of multigrade lubricating oils. Kinematic viscosities at 100°C (8.26±0.03 cSt) and 40°C (36.98±0.01 cSt) were determined according to ASTMD-446 method, while the viscosity index (208±0.11) was determined according to ASTMD-2270 method. A design of experiment (Mixture Design Method using Minitab 17) was used to determine the proportion of PUPO (68.75%), SN 500 (23.75%), and additives (7.50%) that gave the mixture with the optimum quality parameters of the produced biolubricant. The produced biolubricant had kinematic viscosities at 100^oC (10.72±0.13 cSt) and 40°C (59.32±0.20 cSt) respectively, a viscosity index of 173±0.10, flash point of 234±1.13°C, pour point of -31±0.10°C, acid value of 21.04±1.21 mg KOH g-¹, and iodine value of 1.28±1.40 mg I₂ g-¹. The produced biolubricant has quality parameters that are comparable to available biolubricating oil and was also found within standards for engine oils.