Chemistry

Reactivity: potential energy hypersurfaces

Reactivity: potential energy hypersurfaces



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Reaction coordinates

Reaction coordinate
In order to determine the energetically most favorable path for the conversion of the initial state into the end product, the energy is calculated depending on all binding parameters that change during the reaction (potential-energy hypersurface). The energetically most favorable function curve (reaction coordinate) can - with a small number of binding parameters - be easily recognized in the graphic representation of the potential hypersurface.
Example of a potential energy hypersurface

(Fig. 1) shows a 3-dimensional representation of the energy hypersurface for nucleophilic substitution on methyl chloride by a fluoride ion (Finkelstein reaction), calculated using the SCF-MO method. It is assumed that only the carbon-chlorine bond length R (C ... Cl) and the carbon-fluorine bond length R (C ... F) change during the reaction.


Download Inorganic Chemistry: Principles of Structure and Reactivity

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Inorganic chemistry: principles of structure and reactivity

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Inorganic Chemistry & # 8211 Wikipedia

Inorganic chemistry for short AC or inorganic is the chemistry of all carbon-free compounds as well as some exceptions see inorganic substances

Silver iodide is sensitive to light and slowly breaks down into its elements. It turns green-gray in sunlight. AgI dissolves in strong complexing agents such as cyanides or thiocyanates


Selectivity

Selectivity, the ability of a chem. Reaction, an examination method or an operation, to choose between several possibilities. The term S. is used and defined differently in different areas of chemistry.

1) With chem. Reactions that can lead to different products in parallel partial steps are understood by S. the proportion with which a certain target product is formed, taking into account the statistical relationships. The greater this proportion, the more selective the reaction. If the products are constitutional isomers, one speaks of Chemoselectivity & # 228t or regioselectivity, in the case of stereoisomers of Stereoselectivity & # 228t (Stereospecificity & # 228t). Quantitatively, the S. is defined either a) as the ratio of two product concentrations S.12 = c1/ c2or b) as a quotient from the concentration c1 of the target product and the sum of all product concentrations S.1 = c1ci. The range of values ​​is for & # 252r S.12between 0 and & # 8734, that of S.1 between 0 and 1. The S. S.12 is also known as relative reactivity designated. If the same kinetic time laws apply to the formation rates of the various products, the concentrations can be determined by the rate constants k be replaced (complex reaction): S.12 = k1/k2 respectively. S.1 = k1ki. Only in these cases is the rate of a reaction a characteristic constant that is independent of the initial concentration and conversion, but which can be influenced by changes in the reaction conditions (temperature, catalyst, solvent).

2) In the chem. Analytics is called an analytical process selective if it can be used to determine several components in the analytical sample next to one another and independently of one another, i.e. i.e. when the analysis signal of the component to be determined i of the other substances present k is not influenced.

3) In material separation processes using phase equilibria, especially in extraction, extractive distillation and chromatographic methods, S. is understood to mean the influence of the selective solvent on the separability of two components. It characterizes the influence of the intermolecular interactions on the relative solubility or volatility of the two substances. However, the suitability of the respective phase equilibrium for an effective separation of substances does not only depend on the substance, but also on the absorption capacity of the solvent for the two substances, the capacitance. In chromatography, enantioselectivity is becoming increasingly important with the help of chiral stationary phases.


Results and discussion

Synthesis, general properties and efficiency of the polymerization of CDs

CDs made from biomass containing aromatic (CD-1CD-3) and aliphatic structural units (CD-4 and CD-5) are compared with regard to their ability to sensitize the initiation of radical photopolymerization with visible light-emitting LEDs. Solvothermal (CD-1CD-3) and hydrothermal (CD-4, CD-5) Reaction conditions 27 resulted in different amounts of carbon and nitrogen in the depending on the amount of reactant CDs, Table 1. The amount of C − N, C − O, and C = O units differed from each other, which was confirmed by XPS analysis (Figure S2 – S5 in the Supporting Information). CD-1CD-3 are based on different amine concentrations that were used for the synthesis. The examined CDs mainly comprise sp 2 carbon linked by the above heterocyclic units. Working with CDs also requires a rethinking of the experiments to be carried out, since material properties such as oxidation and reduction potentials, excitation and emission properties as well as a cytotoxic reaction represent variable properties that can be controlled by the synthesis process. The answer to a chemical question of a heterogeneous material 21 to be synthesized is essentially known (see above). For this reason, it is very important to know whether such materials can cause toxicological problems. The cytotoxicity shows as a quantity the response to materials taking into account the response of MCF-10A cells in a flow cytometry test. The examined CD-2CD-5 show a viability of greater than 90% of cells while CD-1 still has an acceptable size (Table 1). Cell growth is apparently not inhibited up to a concentration of 400 μg mL −1 (Figure S6 in the Supporting Information, incubation time 4 h). The low cytotoxic reaction enables the design of new green photopolymerization systems with sustainable components. In addition, a rough estimate of the manufacturing costs revealed a higher economic potential for CDs compared to photoinitiating components based on fossil resources. 27


Reactivity

The term Reactivity is generally used as a measure to describe reactions, with different meanings in sociology, chemistry, physics (nuclear engineering) and medicine (pathophysiology and radiology).

Further recommended specialist knowledge

Safe weighing range to ensure accurate results

Daily visual inspection of the laboratory balances

How can you quickly check pipettes?


Reactivity

Reactivity, Responsivenesswho have favourited Chem. Connections to react with others. The R. is not a material constant, but always depends on the type of reaction partner, but also on the reaction conditions such as solvent, temperature or degree of distribution in the case of heterogeneous reactions. Rate constants of the reaction kinetics can serve as quantitative indicators of the R.

An important problem in chemistry is the influence of the electronic and spatial structure of the reaction partners on their R. Such comparisons are particularly possible within the same reaction types, when substances from homologous series or analogous basic bodies with different substituents are converted. Examples of such structure-R.-relationships are the LFE relationships. If a substrate has several reactive centers, the preferred position of attack by the reagent is also important (selectivity). The statement "The more reactive a reagent is, the less selectively it reacts" is often, but not generally, valid (R. selectivity relationships).

You might also be interested in: Spektrum der Wissenschaft 7/2021

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BenzothiazoleNoxides, IV 1) Synthesis and reactivity of 2-cyanobenzothiazoleN-Oxides and 2-benzothiazole carbonitriles

2-carbamoylbenzothiazoleN-oxides 2 2) react with phosphorus oxychloride in pyridine to form the previously unknown highly reactive 2-cyanobenzothiazoleN-oxides 1 whose aqueous-alkaline hydrolysis produces the prototropic 2-hydroxybenzothiazoleN-oxides 4 supplies. 2-benzothiazole carboxamides 8 dehydrate in boiling phosphorus oxychloride to give the 2-benzothiazole carbonitriles 9. Spectroscopic data are discussed.

Abstract

Benzothiazoles N-Oxides, IV 1) Synthesis and Reactivity of 2-Cyanobenzothiazole N-Oxides and 2-Benzothiazolecarbonitriles

2-carbamoylbenzothiazoles N-oxides 2 2) react with phosphoryl chloride in pyridine to produce the hitherto unknown highly reactive 2-cyanobenzothiazole N-oxides 1, whose aqueous alkaline hydrolysis yields prototropic 2-hydroxybenzothiazole N-oxides 4. 2-benzothiazole carboxamides 8 dehydrate in boiling phosphoryl chloride to yield the 2-benzothiazolecarbonitriles 9. Spectroscopic data are discussed.


Medicine

In the physiology and pathophysiology describes the Reactivity the ability of biological tissues to react differently to environmental influences (for example in sensory physiology or as an immune response) and the respective extent of these reactions. In immunology, the term reactivity is also synonymous (e.g. as bronchial hyperresponsiveness common in bronchial asthma).

In radiology and radiation biology, on the other hand, the Reactivity specifically a measure of the sensitivity of tissues to electromagnetic radiation. [1]


Structure and reactivity of the biomolecules

The textbook covers the compulsory material for the basic course in organic chemistry. However, the presentation is from a new perspective. In an interdisciplinary approach, the structure and reactivity of organic molecules as well as the mechanisms of simple reactions in organic chemistry that are relevant in biological processes are explained. Biologically relevant substances and enzymatic reactions create a link to biology.

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The textbook covers the compulsory material for the basic course in organic chemistry. However, the presentation is from a new perspective. In an interdisciplinary approach, the structure and reactivity of organic molecules as well as the mechanisms of simple reactions in organic chemistry that are relevant in biological processes are explained. Biologically relevant substances and enzymatic reactions create a link to biology.

This volume aims to initiate communication between biologists and chemists - something that the leading representatives of the chemical industry are increasingly demanding. The mechanisms of chemical reactions that are relevant in cell metabolism are explained using the example of simple reactions in organic chemistry. The description of related biologically relevant substances or enzymatic reactions establishes the relationship to biology. In contrast to textbooks on biochemistry, both primary metabolites, including their prebiotic formation, and important natural substances are taken into account.
In addition, the basics of the structure and reactivity of organic molecules are described. The scope of this section is based on the required workload of a modern university basic course in organic chemistry. This of course includes the nomenclature and etymology of the technical terms. The examples of natural and artificial products give an insight into the variety of substances that shape our everyday life and arouse interest in studying the chemistry of biological processes beyond the scope of the textbook.
More than 100 life works of famous scientists illustrate the great achievements of modern chemistry and physics in the 20th century.

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Relationship between the atomic number and the chemical reactivity of alkali metals

Alkali metals are white, highly reactive substances that can easily be cut with a knife. All six can be found in Group I of the Periodic Table, which lists elements in order of increasing atomic number. the Atomic number is the number of protons in the nucleus of an atom. Neutrons are also in the nucleus, but they have little influence on chemical reactivity. The alkali metals in increasing atomic number are lithium, sodium, potassium, rubidium, cesium and francium.


Potassium in water

Alkali metals form alkali lyes with water, releasing hydrogen. The reactivity increases from lithium to cesium. While lithium does not ignite on contact with water, potassium burns immediately and cesium even explodes on contact with water. If carried out correctly, this behavior of the alkali metals with potassium can be demonstrated relatively harmlessly - but nevertheless impressively.

Level of difficulty

Devices

(Plastic) tub, filter paper, tweezers, knife

Chemicals

0.1% phenolphthalein solution. (ethanolic)

Note

Potassium forms peroxides and superoxides (yellow or red crusts) after long storage. When cut, these would ignite the potassium immediately or even lead to a detonation. Only carry out the experiment if you have appropriate experience with alkali metals!

Execution

The tub is three-quarters filled with water and a filter paper is placed in the middle of the tub on the surface of the water. Now a piece of potassium about the size of a pinhead - which has previously been de-encrusted with a knife and freed from the protective liquid with a kitchen roll - is carefully placed on the filter paper. The potassium ignites immediately on contact with water and burns with a purple flame. After the reaction, a few drops of phenolphthalein solution are added to the water - a color change can be observed.

Annotation

The experiment must be carried out away from flammable objects!

Disposal

The resulting potassium hydroxide solution is neutralized and can be disposed of in the drain.

All devices and papers are treated with water to remove any small bits of potassium that may adhere to them.

Explanation

When alkali metals such as potassium come into contact with water, a violent exothermic reaction occurs with the release of hydrogen.

The resulting potassium hydroxide dissolves in the water and forms a weak potassium hydroxide solution, which is why phenolphthalein turns purple.