My Chemistry

The chemical reaction

The chemical reaction is a process that leads to the transformation of a set of other chemical substances [1]. Chemical reactions can be spontaneous, requiring no energy input, or non-spontaneous, usually following the input of some kind of energy, such as heat, light or electricity. Classically, chemical reactions including changes that involve the movement of electrons in a tight formation and breaking of chemical bonds, although the general concept of chemical reactions, particularly the idea of a chemical equation, valid for the transformation of elementary particles (as illustrated by the Feynman diagrams), as well as nuclear reactions.
The substance (or substances) initially involved in a chemical reaction are called reactants or reagents. Chemical reactions are usually characterized by chemical changes, and they produce one or more products, which usually have different properties than the reactants. The reaction often consists of a sequence of individual sub-steps, which are called elementary reactions, and information regarding the proper course of action is part of the reaction mechanism. Chemical reactions are described with chemical equations, which graphically presents the starting material, the final product, and sometimes intermediate products and reaction conditions.
Different chemical reactions used in combinations in chemical synthesis to obtain the desired product. In biochemistry, series of chemical reactions catalyzed by enzymes form metabolic pathways, in which the synthesis and decomposition under ordinary conditions is not possible in the cell. Contents

     [Edit] History Antoine Lavoisier developed the theory of combustion as a chemical reaction with oxygen
Chemical reactions such as burning in the fire, fermentation and reduction of ore to metal known since antiquity. Initial theory of transformation of materials were developed by Greek philosophers, such as Theory of Four Elements of Empedocles states that every substance consists of four basic elements - fire, water, air and earth. In the Middle Ages, alchemists studied by chemical transformation. They sought, in particular, to turn lead into gold, which purpose they used the reaction with the alloy of lead and copper-sulfur. [2]
Production of chemical substances that are not normally occur in nature have long tried, such as sulfuric and nitric acid synthesis caused by the alchemist Jabir ibn Hayyan controversial. This process involves heating of minerals such as copper sulfate and nitrate, sulfate alum and saltpeter. In the 17th century, Johann Rudolph Glauber produce hydrochloric acid and sodium sulphate by reacting sulfuric acid and sodium chloride. With the development of the main hall in 1746 and Leblanc process, enabling large scale production of sulfuric acid and sodium carbonate, respectively, the chemical reaction to be implemented into the industry. Further optimization of the technology produces sulfuric acid contact process in 1880, [3] and Haber process was developed in 1909-1910 for the synthesis of ammonia. [4]
From the 16th century, researchers including Jan Baptist van Helmont, Robert Boyle and Isaac Newton tried to build theories of chemical transformations observed experimentally. Phlogiston theory proposed in 1667 by Johann Joachim Becher. It postulated the existence of fire-like element called "phlogiston", which is contained in the body burned and released during combustion. This was proven false in 1785 by Antoine Lavoisier who discovered the true explanation of combustion as a reaction with oxygen from the air. [5]
Joseph Louis Gay-Lussac in 1808 recognized that the gas is always react in a certain relationship with one another. Based on the ideas and the atomic theory John Dalton, Joseph Proust had developed a definite law of proportion, which later resulted in the concept of stoichiometry and chemical equations. [6]
About organic chemistry, it is long believed that a compound derived from living organisms are too complex to be obtained synthetically. According to the concept of vitalism, organic matter is endowed with "vital force" and are distinguished from inorganic materials. The separation is ended, but with the synthesis of urea from inorganic precursors by Friedrich Wöhler in 1828. Other chemists who bring a major contribution to organic chemistry include the synthesis of Alexander William Williamson ether and Christopher Kelk Ingold, who among many inventions, set up mechanisms of substitution reactions. [Edit] Equation
Chemical equations are used to graphically describe the chemical reaction. They consist of chemical or structural formulas of the reactants on the left and those on the right products. They are separated by an arrow (→) which indicates the direction and type of reaction. Tip of the arrow points in the direction in which the reaction products. A double arrow (in equilibrium with) pointing in the opposite direction is used for the reaction equilibrium. Equation must be balanced according to the stoichiometry, the number of atoms of each species should be equal on both sides of the equation. This is achieved by the scale of the number of molecules involved (A, B, C and D in the example schematic below) by the appropriate integers a, b, c and d. [7]

    \ Mathrm {a \ a + b \ B \ longrightarrow C \ C + d \ D}
More complex reaction represented by reaction scheme, which in addition to the starting materials and intermediate products is important or shows a state transition. Also, some additions are relatively small for the reaction can be shown in the above reaction arrows; example is the addition of water, heat, lighting, catalysts, etc. Similarly, some minor products can be placed below the arrow, often with a minus sign. Examples of organic reactions: oxidation of ketones to esters with peroxycarboxylic acids
Retrosynthetic analysis can be applied to design the synthesis of complex reactions. Here the analysis starts from the product, for example by splitting chemical bonds are selected, to arrive at a reasonable initial reagents. A special arrow (⇒) is used in the retro reaction. [8] [Edit] Elementary Reaction
The fundamental reaction is the smallest division in which chemical reactions can be decomposed into, it has no intermediate products. [9] Most reactions were observed experimentally constructed of many elementary reactions that occur in parallel or sequentially. Actual sequence of individual fundamental reaction is known as the reaction mechanism. Basic reaction involves several molecules, usually one or two, because the low probability for a molecule to meet at a certain time [10]. Azobenzene isomerization, induced by light (hν) or heat (Δ)
The most important basic reaction is unimolecular and bimolecular reactions. Only one molecule is involved in the unimolecular reaction, but be transformed by isomerization or dissociation in one or more other molecules. These reactions require the addition of energy in the form of heat or light. A typical example of unimolecular reaction is cis-trans isomerization, in which the cis-form compound converts to trans-form or vice versa [11].
In a typical dissociation reaction, bonds in the molecule splits to produce two molecular fragments. Homolytic or heterolytic splitting can. In the first case, the bonds are divided so that each product maintains the electron and the neutral radical. In the second case, the two electrons from chemical bonds to stick with one product, generating charged ions. Dissociation plays an important role in triggering a chain reaction, such as hydrogen-oxygen or polymerization reaction.

    \ Mathrm {AB \ longrightarrow A + B}
    AB molecule dissociation into fragments A and B
For the bimolecular reaction, two molecules collide and react with each other. Mergers they are called chemical synthesis or addition reactions.

    \ Mathrm {A + B \ longrightarrow AB}
Another possibility is that only partially transferred from one molecule to another molecule. This type of reaction occurs, for example, in redox reactions and acid-base. In redox reactions, the particle is an electron transfer, whereas in acid-base reaction is a proton. This type is also called a metathesis reaction.

    \ Mathrm {HA + B \ longrightarrow A + HB}
for example

    NaCl (aq) + AgNO3 (aq) → NaNO3 (aq) + AgCl (s)
[Edit] Chemical equilibrium Main article: chemical equilibrium
Most of the reversible chemical reaction, which they can and do run in both directions. Forward and reverse reactions compete with each other and differ in the rate of reaction. This price depends on the concentration and therefore change with reaction time: backward rate gradually increased and became similar to the reaction rate in the future, building the so-called chemical equilibrium. The time to reach equilibrium depends on parameters such as temperature, pressure and materials involved, and determined by the free energy minimum. In equilibrium, the Gibbs free energy must be zero. Pressure dependence can be explained by Le Chatelier's principle. For example, an increase in pressure due to decreased volume causes the reaction to shift to the side with less moles of gas [12].
Reaction products are stable at equilibrium, but can be improved by removing the product from the reaction mixture or an increase in temperature or pressure. Changes in initial concentrations of the substances did not affect the equilibrium. [Edit] Thermodynamics
The chemical reaction is determined by the laws of thermodynamics. The reaction can proceed alone if they are exergonic, ie if they release energy. Corresponding reaction free energy consists of two different thermodynamic quantities, enthalpy and entropy: [13]

    \ Mathrm {\ Delta G = \ Delta H - T \ cdot \ Delta S}
    G: free energy, H: enthalpy, T: temperature, S: entropy, Δ: the difference
Exothermic reaction can be, where ΔH is negative and energy is released. Typical examples of exothermic reactions are precipitation and crystallization, in which the ordered solids formed from the gas phase or liquid regularly. In contrast, the endothermic reaction, heat is consumed from the environment. This can occur by increasing the entropy of the system, often through the formation of gaseous reaction products, which have high entropy. Because entropy increases with temperature, endothermic reaction preferably takes place at temperatures much higher. On, much like the opposite reaction exothermic crystallization occurs at low temperatures. Changes in temperature can sometimes reverse the direction of the reaction, as in the Boudouard reaction:

    \ Mathrm {CO_2 + C \ rightleftharpoons 2 \ CO \; \ quad \ Delta H = 172.45 \ kJ \ cdot mol ^ {-1}}
The reaction between carbon dioxide and carbon to form carbon monoxide is an endothermic reaction at temperatures above about 800 ° C and below this temperature exothermic. [14]
The reaction can also be characterized by internal energy that takes into account changes in potential entropy, volume and chemistry. The latter is dependent, among other things, the activities of agents involved. [15]

    \ Mathrm {d} U = T \, {d} S - p \, {d} V + \ mu \, {d} n \!
    U: internal energy, S: entropy, p: pressure, μ: chemical potential, n: number of molecules, d: a sign of minor changes
[Edit] Kinetics
The speed at which the reaction is studied by reaction kinetics. Rate depends on various parameters, such as:

    * The concentration of reactants, which usually make the reaction happen at a faster rate if raised through increased collisions per unit time. Some reactions, however, have high levels that are independent of the concentration of the reactants. This is called zero-order reaction.
    * The surface area available for contact between the reactants, in which solid, especially in heterogeneous systems. Larger surface area produces a higher reaction rate.
    * Pressure - increases the pressure decreases the volume between the molecules and hence increase the frequency of collisions between molecules.
    * Activation energy, which is defined as the amount of energy required to create the initial reaction and continue spontaneously. Higher activation energy indicates that the reactants need more energy to start than a reaction with a lower activation energy.
    * The temperature, which accelerates the reaction, if raised, due to higher temperatures increase the energy of the molecules, creating more collisions per unit time,
    * The presence or absence of catalysts. Catalysts are substances that change the pathway (mechanism) reaction which in turn increases the reaction rate by lowering the activation energy required for the reaction. The catalyst is not destroyed or changed during the reaction, so it can be used again.
    * For some reactions, the presence of electromagnetic radiation, especially ultraviolet light, it is necessary to promote the breaking of bonds to start the reaction. This is particularly true for reactions involving radicals.
Some theories allow to calculate the rate of reaction at the molecular level. This field is called the reaction dynamics. V first-order reaction rate, which could disintegration agent A, is given by:

    v = - \ frac {d [\ mathrm {A}]} {dt} = k \ cdot [\ mathrm {A}]
Its integration results:

    \ Mathrm {[A]} (t) = \ mathrm {[A]} _ {0} \ cdot e ^ {-k \ cdot t}
Here k is a first-order rate constant has dimensions 1/time, [A] (t) is the concentration at time t and [A] 0 is the initial concentration. First-order reaction rate depends only on the concentration and properties of substances involved, and the reaction itself can be described by the characteristic beak. More than one time constant is needed when explaining the high-order reaction. Temperature dependence of rate constants typically follows the Arrhenius equation:

    k = e ^ {k_0-E_a {} / K_ {B} {T}}
where Ea is the activation energy and kB is Boltzmann's constant. One of the simplest model of the reaction rate is the theory of collisions. More realistic models tailored to the specific problem and including the transition state theory, the calculation of potential energy surfaces, the theory of Marcus and Rice-Ramsperger-Kassel-Marcus (RRKM) theory. [16] [Edit] Reaksi type [Edit] The four basic types [Edit] Synthesis
In the synthesis reaction, two or more simple substances combine to form more complex substances. Two or more reactants produce one product is another way to identify a synthesis reaction. For example, simple hydrogen gas combined with simple oxygen gas can produce a more complex substance, like water. [17] [Edit] Decomposition
Decomposition reaction is the opposite of synthesis reactions, in which a more complex substance breaks down into parts that are much simpler [17]. [18] [Edit] Single replacement
In a single replacement reaction, a single free element replaces another in a compound. [17] [Edit] Double replacement
In a double replacement reaction, part of the two compounds switch places to form two new compounds [17]. This is when the anions and cations of two different molecules switch places, forming two entirely different compounds. [18] These reactions are in general form:
AB + CD ---> AD + CB
One example of a double displacement reaction is the reaction of lead (II) nitrate with potassium iodide to form lead (II) iodide and potassium nitrate:
Pb (NO3) 2 + 2 KI ---> PbI2 + 2 KNO3 [Edit] Oxidation and reduction Illustration of a redox reaction Two sections of the redox reaction
Redox reactions can be understood in terms of electron transfer from one species is involved (reducing agent) to another (oxidation agent). In this process, oxidized species of the former and the latter is reduced, so that the redox-term. Although sufficient for many purposes, these descriptions are not exactly correct. Oxidation is better defined as an increase in oxidation, and reduction as a decrease in oxidation number. In practice, the transfer of electrons will always cause a change in oxidation number, but there are many reactions that are classified as "redox" even though no electron transfer occurs (such as those involving covalent bonds) [19]. [20]
Examples of redox reactions are:

    2 S2O32-(aq) + I2 (aq) → S4O62-(aq) + 2 I-(aq)
Here I2 is reduced to I-and S2O32-(thiosulfate anion) is oxidized to S4O62-.
Which of the reactants involved would reduce or oxidizing agents can be predicted from the electronegativity of their elements. Elements with low electronegativity, such as most metals, easily donate electrons and oxidize - they are reducing agents. On, contrary to many ions with high oxidation states, such as H2O2, MnO- 4, CrO3, Cr2O2- 7, OsO4) can get an extra one or two electrons and strong oxidizing agents.
The number of electrons donated or received in the redox reaction can be predicted from the electron configuration of elements of the reactants. Elements trying to achieve a low-energy configuration of noble gases and alkali metals and halogens so that it will donate and accept one electron, respectively, and their own noble gases are chemically inactive. [21]
An important class of redox reactions are electrochemical reactions, where the electrons from the power supply is used as a reducing agent. These reactions are very important for the production of chemical elements, such as chlorine [22] or aluminum. The reverse process in which electrons are released in redox reactions and can be used as electrical energy is possible and is used in batteries. [Edit] complexation Ferrocene - a metal atom sandwiched between two C5H5 ligands
In complexation reactions, some ligands react with metal atoms to form coordination complexes. This is achieved by providing a free electron pair of the ligand to empty orbitals of the metal atoms and form a bond dipole. Lewis base ligands, they can both ions and neutral molecules, such as carbon monoxide or ammonia water. The number of ligands that react with the central metal atom can be found using the 18-electron rule, saying that the transition metal valence shells will collectively hold 18 electrons, while the symmetry of the resulting complex can be predicted by crystal field theory and ligand field theory. Complexation reactions also include the exchange of ligands, in which one or more ligands are replaced by others, and redox processes that change the oxidation state of the central metal atom. [23] [Edit] Acid-base reactions
Acid-base reactions involve proton transfer from one molecule (acid) to another (base). Here, the acid acts as proton donors and bases as acceptors.

    \ Mathrm {HA + B \ rightleftharpoons A ^ - ^ HB + +}
    Acid-base reaction, HA: acid, B: Base, A-: conjugated base, HB +: acid conjugation
Results related to proton transfer in the so-called conjugate acid and conjugate base [24]. Reverse reaction is possible, and thus the acid / base and the conjugated base / acid is always in equilibrium. Equilibrium is determined by the acid and base dissociation constants (Ka and Kb) of the substances involved. A special case of acid-base reaction is the neutralization of acids and bases which, taken at exactly the same amount, form a neutral salt.
Acid-base reactions can have different definitions depending on the acid-base concept works. Some of the most common are:

    * Arrhenius definition: Acids dissociate in water releasing H3O + ions; bases dissociate in water releasing OH-ions.
    Brønsted-Lowry * Definition: Acids are proton (H +) donor, proton acceptor bases, this includes the definition of Arrhenius.
    * Lewis definition: Acids are electron-acceptor pairs, base-pair electron donors, including the Brønsted-Lowry definition.
[Edit] rain Precipitation
Precipitation is the formation of a solid in a solid solution or in the other during a chemical reaction. This usually occurs when the concentration of dissolved ions exceed the solubility limit [25] and form soluble salts. This process can be helped by adding a precipitating agent or by removal of solvent. Rapid precipitation results in a residual amorphous or microcrystalline and slow process that can produce single crystals. The latter can also be obtained by recrystallization of microcrystalline salt. [26] [Edit] Solid-state reaction
The reaction can take place between two solids. However, because the rate of diffusion in solids is relatively small, the corresponding chemical reaction is very slow. They are accelerated by increasing the reaction temperature and finely divided reactants to increase the surface area contact. [27] [Edit] photochemical reaction In the Paterno-Buchi reaction, a photoexcited carbonyl group is added to an excited olefin, yielding an oxetane.
In photochemical reactions, atoms and molecules absorb energy (photons) of light illumination and convert into an excited state. They can then release this energy by breaking chemical bonds, thus producing radicals. Photochemical reactions including the reaction of hydrogen-oxygen, radical polymerization, a chain reaction and the reaction rearrangement. [28]
Important process that involves photochemistry. The main example is photosynthesis, where most plants use solar energy to convert carbon dioxide and water into glucose, oxygen as a byproduct. Humans rely on photochemistry for the formation of vitamin D, and vision is initiated by the photochemical reaction of rhodopsin [11] On the fireflies., Enzymes catalyze reactions in the stomach that produce bioluminescence [29]. Many significant photochemical reactions, such as ozone formation, occurring in Earth's atmosphere and the atmospheric chemistry. [Edit] Catalysis Schematic potential energy diagram showing the effect of the catalyst in an endothermic chemical reaction. The presence of the catalyst opens a different reaction pathway (red) with a lower activation energy. The end result is the same and the overall thermodynamics. Solid heterogeneous catalysts plated on meshes in ceramic catalytic converters in order to maximize their surface area. This converter exhaust from Peugeot S2 106 1100
In catalysis, the reaction takes place not directly but through a third substance known as a catalyst. Unlike other reagents that participate in chemical reactions, the catalyst is not consumed by the reaction itself, but can be inhibited, disabled or destroyed by secondary processes. The catalyst can be used in different phases (heterogeneous) or in the same phase (homogeneous) as reactants. In heterogeneous catalysis, typical secondary processes include coking where the catalyst is a side product that is covered by the polymer. In addition, heterogeneous catalysts can dissolve into the solution in the system solid-liquid or vaporized in a gas-solid system. The catalyst can only accelerate the reaction - a chemical that slows down the reaction so-called inhibitors [30] [31] A substance that increases the activity of catalysts called a promoter, and a substance called catalyst poisons catalytic disable .. With the catalyst, the reaction is inhibited by activation of high kinetic energy can occur in circumvention of the activation energy.
Heterogeneous catalysts are usually solid, powder to maximize their surface area. Very important in heterogeneous catalysis is the platinum group metals and other transition metals, which are used in hydrogenations, catalytic reforming and in the synthesis of commodity chemicals such as nitric acid and ammonia. Acid is an example of homogeneous catalysts, they increase the nucleophilicity of the carbonyl, allowing the reaction that would not otherwise proceed with the electrophile. The advantage of homogeneous catalysts is the ease of mixing them with the reactants, but they also may be difficult to separate from the product. Therefore, heterogeneous catalysts are preferred in many industrial processes. [32] [Edit] The reaction in organic chemistry
In organic chemistry, in addition to oxidation, reduction or acid-base, a number of other reactions can occur that involve covalent bonds between carbon atoms or carbon and heteroatoms (such as oxygen, nitrogen, halogen, etc.). Many specific reactions in organic chemistry is the name of the designated reaction after their discoverer. [Edit] Substitution
In substitution reactions, functional groups within a particular chemical compound is replaced by another group [33]. These reactions can be distinguished by the types of species into replacing the substitution, electrophilic or nucleophilic radicals. SN1 Mechanism Sn2 mechanism
In the first type, a nucleophile, an atom or molecule with an excess of electrons and thus a negative charge or partial charge, replaces another atom or molecule part of the "substrate". Electron pair of the nucleophile attacks the substrate to form a new bond, while the group left off with a pair of electrons. Nucleophiles may be electrically neutral or negatively charged, while the substrate is usually neutral or positively charged. Examples of ion nucleophile is hydroxide, alkoxides, amines, and halides. This type of reaction is found mainly in aliphatic hydrocarbons, aromatic hydrocarbons and rarely in. The latter has a high electron density and nucleophilic aromatic substitution in only with groups that strongly attract electrons. Nucleophilic substitution can occur via two different mechanisms, SN1 and Sn2. In their name, the S stands for substitution, N for nucleophilic, and the numbers represent the unimolecular kinetic sequence, or a bimolecular reaction. [34] Three steps of Sn2 reactions. Nucleophile and leaving group is red-green Sn2 reaction causes inversion of the stereo (Walden inversion)
SN1 reaction proceeds in two steps. First, the group leaves removed to create a carbocation. This is followed by rapid reaction with these nucleophiles. [35]
In the Sn2 mechanism, nucleophiles form transition states with molecular attack, and only then leave the group split. These two mechanisms differ in the stereochemistry of the product. SN1 leads to the addition of non-stereospecific and did not lead to a chiral center, but rather in a set of geometric isomers (cis / trans). In contrast, inversion (Walden inversion) of stereochemistry preexisting observed in Sn2 mechanism. [36]
Electrophilic substitution is a partner of nucleophilic substitution in the attacking atom or molecule, an electrophile, has a low electron density so that the positive charge. Typical electrophile is the carbonyl carbon atom groups, carbocation or sulfur or nitronium cation. This reaction occurs almost exclusively in aromatic hydrocarbons, which are called electrophilic aromatic substitution. Attacking electrophile results in what is called a σ-complex, transition state in which the aromatic system is abolished. Later, the group left, usually protons, is split off and aromaticity restored. An alternative for electrophilic aromatic substitution of an aliphatic substitution. This is similar to aliphatic nucleophilic substitution and also has two major types, SE1 and SE2 [37] The mechanism of electrophilic aromatic substitution
In a third type of substitution reaction, radical substitution, the particle is a radical attack [33]. This process usually takes the form of a chain reaction, for example in alkane reactions with halogens. In the first step, light or heat destroyed halogen-containing molecules to produce radicals. Then the reaction as a result of the avalanche until two radicals meet and recombine. [38]

    \ Mathrm {X {\ cdot {} + R - H} \ longrightarrow X {-} H + R {\ cdot}}
    \ Mathrm {R {\ cdot} + X_2 \ longrightarrow R {-} {X + X \ cdot}}
    Radical chain reaction during the substitution reaction
[Edit] Additions and deletions
Addition and colleagues, deletion, is a reaction that converts the number of substituents on the carbon atoms, and bond forms or multiple splitting. Double and triple bonds can be produced by removing the leaving group match. Similar to the nucleophilic substitution, there are several possible reaction mechanism is named after the order of the reaction respectively. In the E1 mechanism, leaving the group issued the first, forming a carbocation. The next step, the formation of double bonds, takes place with elimination of a proton (deprotonation). The order left inverse in E1cb mechanism, namely the proton divided first. This mechanism requires the participation of the base [39] For similar conditions, both reactions in the deletion of E1 or E1cb always compete with SN1 substitution .. [40]
E1 elimination
E1cb elimination E2 elimination
E2 mechanism also requires a basic, but there is a basic attack and leaving group elimination proceed simultaneously and did not generate ionic intermediate. Unlike the E1 elimination, different stereochemical configurations are possible for the reaction products in the mechanism of E2, because the attack occurred in a special basis of anti-position with respect to leave the group. Because similar conditions and reagents, the elimination of E2 are always in competition with Sn2-substitution. [41] Electrophilic addition of hydrogen bromide
The partners are the additional elimination in which double or triple bonds are converted into single bonds. Similar to the substitution reaction, there are several additional types of particles are distinguished by the type of attack. For example, in the electrophilic addition of hydrogen bromide, an electrophile (proton) attack the double bond form a carbocation, which then reacts with nucleophiles (bromine). Carbocations can be formed on both sides of the double bond depends on the group attached to its ends, and the preferred configuration can be predicted by the Markovnikov rule. [42] This rule states that "In the heterolytic addition of a polar molecule to an alkene or alkyne, which is more electronegative (nucleophilic) atom (or part) of the polar molecule becomes attached to the carbon atom that carries a small amount of hydrogen atoms" [43].
If the addition of functional groups take place at the less substituted carbon atom of the double bond, then the electrophilic substitution with acid is not possible. In this case, one must use a hydroboration-oxidation reaction, in which the first step, the boron atom acts as an electrophile and adds less substituted carbon atom. In the second step, nucleophilic hydroperoxide anion halogen or boron atom attack. [44]
While the addition to electron-rich alkenes and alkynes particularly electrophilic, nucleophilic addition plays an important role for carbon-hetero multiple bonds, and especially the representatives of the most important, the carbonyl group. This process is often associated with an elimination, so that after the reaction of the carbonyl group is present again. Hence the addition-elimination reaction and can occur in carboxylic acid derivatives such as chlorides, esters or anhydrides. This reaction is catalyzed by acid or base often, where the acid increases with the electrophilicity of the carbonyl group with the binding of oxygen atoms, while the base increased nucleophilicity of the attacking nucleophile. [45] Acid catalyst addition-elimination mechanism
Nucleophilic addition of carbanion or other nucleophiles to the double bond of alpha, beta-unsaturated carbonyl compounds can proceed via the Michael reaction, which included a larger class of conjugate additions. This is one of the most useful method for CC bond formation mild [46]. [47] [48]
Some additions that can not be executed with nucleophiles and electrophiles, can be managed by free radicals. As with the free radical substitution, as a result of the addition of radical chain reactions, and reactions are the basis of free radical polymerization. [49] [Edit] Other mechanisms of organic reactions Cope rearrangement of 3-methyl-1 ,5-hexadiene Diels-Alder reaction mechanism Orbital overlap in Diels-Alder reaction
In the rearrangement reaction, the carbon skeleton of molecules is repeated to give a structural isomer of the original molecule. These include hydride shift reaction such as Wagner-Meerwein rearrangement, in which hydrogen, alkyl or aryl group migrates from one carbon to carbon neighbors. Most of the rearrangements associated with the breaking and formation of new carbon-carbon bond. Another example is the reaction of such sigmatropic Cope rearrangement. [50]
Cyclic rearrangements including cycloadditions and, more generally, pericyclic reactions, where two or more double bond-containing molecules form a cyclic molecule. An important example of the cycloaddition reaction is the Diels-Alder reaction (called a [4 +2] cycloaddition) between a conjugated diene and substituted alkenes to form a substituted cyclohexene system. [51]
Whether or not a particular cycloaddition will proceed depending on the electronic orbitals of the participating species, such as orbital only with the same sign of the wave functions will overlap and interact constructively to form a new bond. Cycloaddition is usually aided by light or heat. These disorders result in different arrangements of electrons in the excited state of the molecules involved and therefore different effects. For example, [4 +2] Diels-Alder reaction may be assisted by the heat while the [2 +2] cycloaddition is selectively induced by light. [52] Because of the orbital character, potential to develop the stereoisomeric cycloaddition products is limited, as described by Woodward-Hoffmann rules [53]. [Edit] Reaction of Biochemistry Illustration of model fit due to enzyme activity
Biochemical reaction is mainly controlled by the enzyme. These proteins can specifically catalyze a single reaction, so the reaction can be controlled very precisely. The reaction takes place in the active site, a fraction of the enzyme that normally found in a pocket or cleft bounded by amino acid residues, and the rest of the enzymes that are used primarily for stabilization. Catalytic action of enzymes depend on several mechanisms including molecular form ("induced fit"), strain the bonds, the proximity and orientation relative to the enzyme molecule, proton donation or withdrawal (acid / base catalysis), electrostatic interactions and many others. [54]
Biochemical reactions that occur in living organisms are collectively known as metabolism. Among the most important is the mechanism of anabolism, in which different DNA and enzyme-controlled process results in the production of large molecules such as proteins and carbohydrates from smaller units [55]. Bioenergetics research sources of energy for this reaction. An important energy source is glucose, which can be produced by plants through photosynthesis or assimilation of food. All organisms use this energy to produce adenosine triphosphate (ATP), which can then be used for any other reaction energy. [Edit] Applications Thermite reactions proceed in welding rail. Shortly after this, the liquid iron flows into the mold around the rail gap
Chemical reactions are central to chemical engineering in which they are used for the synthesis of new compounds from natural raw materials such as petroleum and mineral ores. It is important to make the reaction as efficiently as possible, to maximize yield and minimize the amount of reagents, energy inputs and waste. Catalysts are very helpful for reducing the energy required for the reaction and increases its reaction rate [56] [57].
Some specific reactions have their niche applications. For example, the thermite reaction is used to generate light and heat in fireworks and welding. Although less controlled than oxy-fuel welding the more conventional arc welding and flash welding, requires much less equipment and is still used to fix the rails, especially in remote areas. [58] [Edit] Monitoring
Monitoring mechanisms of chemical reactions is very dependent on the reaction rate. Relatively slow process can be analyzed in situ for the concentration and identity of each ingredient. Important analytical tool for real-time measurement of pH and analysis of optical absorption (color) and emission spectra. A method that is less accessible but more efficient is the introduction of radioactive isotopes into the reaction and monitoring how it changes from time to time and where to move, this method is often used to analyze the redistribution of substances in the human body. Faster reaction is usually studied by ultrafast laser spectroscopy where the use of femtosecond laser allows short transition countries to be monitored at the time reduced to a few femtoseconds [59]. [

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chemical Reaction

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