Reaction intermediate A species that

The free O atom in the second mechanism is a reaction intermediate, a species that plays a role in a reaction but does not appear in the chemical equation for the overall reaction it is produced in one step but is used up in a later step. The two equations for the elementary reactions add together to give the equation for the overall reaction. 

A reaction mechanism is a special kind of model unique to each reaction. For example, in the decomposition of ozone, 2 0,(g) - 3 02(g), we could imagine the reaction occurring in one step, when two O, molecules collide and rearrange their six atoms to form three 02 molecules (Fig. 13.22). Alternatively, we could imagine a mechanism involving two elementary reactions in the first step, an 03 molecule is energized by solar radiation and dissociates into an O atom and an 02 molecule. Then, in a second step, the O atom attacks another O, molecule to produce two more 02 molecules (Fig. 13.23). The O atom in the second mechanism is a reaction intermediate, a species that plays a role in a reaction but does not appear in the chemical equation for the overall reaction. 

Reaction intermediate A species that is produced and then entirely consumed during a multistep reaction usually shortlived. 

If you add together the three equations above, you will get the overall equation A + 2B E + F. C and D are reaction intermediates, chemical species that are produced and consumed during the reaction, but that do not appear in the overall reaction. 

In the preceding mechanism, the carbocation was an intermediate (a species that exists for a short time during the reaction). The form of the intermediate is often essential to understanding the mechanism. The curved arrows help you in drawing the intermediate. Because you can use curved arrows in only three ways (bond to lone pair, bond to bond, and lone pair to bond), you have limited options for drawing intermediates. 

Under some circumstances, the question arises as to whether the carbene has a finite lifetime, and in some cases a completely free carbene structure is never attained. When a reaction involves a species that reacts as expected for a carbene, but must still be at least partially bound to other atoms, the term carbenoid is applied. Some reactions that proceed by carbene-like processes involve transition-metal ions. In many of these reactions, the divalent carbene is bound to the transition metal. Some compounds of this type are stable whereas others exist only as transient intermediates. 

For the reaction between nitrogen dioxide and carbon monoxide, the mechanism is thought to involve the steps shown in Fig. 15.8, where k1 and k2 are the rate constants of the individual reactions. In this mechanism gaseous N03 is an intermediate, a species that is neither a reactant nor a product but that is formed and consumed during the reaction sequence (see Fig. 15.8). 

Intermediate a species that is neither a reactant nor a product but that is formed and consumed in the reaction sequence. (15.6)... 

These results establish that there is a partitioning between the y-elimination and replacement pathways that occurs from the 300-nm intermediate, a species that is common to both reaction pathways. Based upon the spectra of PLP-compounds in solution, this intermediate is almost certainly a pyridoxamine form of the cofactor-substrate adduct. Removal of the a-proton and subsequent protonation at the C-4 position of the cofactor would effectively remove electron density from the a-carbon (scheme II). The resulting protonated imine would effectively increase the acidity of the (f-carbon protons. The P-carbanion produced by abstraction of a P-proton may then lend anchimeric assistance toward elimination of the y-substituent and formation of a P-y unsaturated... 

Intermediate. A species that appears in the mechanism of the reaction (that is, the elementary steps) but not in the overall balanced equation. (13.5) Intermolecular forces. Attractive forces that exist among molecules. (11.2) International System of Units. A system of units based on metric units. (1.7) Intramolecular forces. Forces that hold atoms together in a molecnle. (11.2) Ion. A charged particle formed when a neutral atom or group of atoms gain or lose one or more electrons. (2.5)... 

The mechanisms of most common reactions consist of two or more elementary steps, reactions that occur in one step and depict a single chemical change. The molecu-larity of an elementary step equals the number of reactant particles and is the same as the reaction order of its rate law. Unimolecular and bimolecular steps are common. The rate-determining, or rate-limiting (slowest), step determines how fast the overall reaction occurs, and its rate law represents the overall rate law. Reaction intermediates are species that form in one step and react in a later one. The steps in a... 

Reaction intermediate A species other than the reactants and products that is proposed to be involved in a reaction mechanism. 

Reaction intermediate A species on the reaction path, neither the initial nor the final comer that has a finite lifetime under the reaction conditions... 

A chemical equation describes the overall result of a chemical reaction that may take place in one or more steps. The steps are called elementary reactions, and the set of elementary reactions that describes what is happening at the molecular level in an overall reaction is called the reaction mechanism. In some cases, the overall reaction involves a reaction intermediate—a species produced in one step but used up in a subsequent one. The rate of the overall reaction depends on the rate of the slowest step (the rate-determining step). This rate is proportional to the product of the concentrations of each reactant molecule in that step. If this step involves a reaction intermediate, its concentration can be eliminated by using the relationship of the concentrations in the preceding fast, equilibrium step. 

Reactant a starting substance in a chemical reaction. (2.9) Reaction intermediate a species produced during a reaction that does not appear in the net equation because it reacts in a subsequent step in the mechanism. (14.7)... 

A reactant commonly produces an intermediate, a species that does not appear in the overall chemical equation for the reaction but which has been invoked in the mechanism. Biochemical processes are often elaborate versions of this simple model. For instance, the restriction enzyme EcoRI catalyzes the cleavage of DNA at a specific sequence of nucleotides (at GAATTC, making the cut between G and A on both strands). The reaction sequence it brings about is... 

A species that is produced in one step of a reaction mechanism and subsequently consumed in another step is called an intermediate. A species that is first consumed and later regenerated is called a catalyst. Neither intermediates nor catalysts appear in the overall balanced equation. 

Alternatively a Mannich-like pathway may be followed (see Mannich reaction), where ammonia reacts with the aldehyde 1 to give an intermediate iminium species, that adds hydrogen cyanide to give the a-amino nitrile 2. The actual mechanistic pathway followed depends on substrate structure and reaction conditions. 

Many reactions take place in more than one step and involve the formation of a reaction intermediate. An intermediate is a species that lies at an energy minimum between steps on the reaction curve and is formed briefly during the course of a reaction. 

Intermediate (Section 5.10) A species that is formed during the course of a multistep reaction but is not the final product. Intermediates are more stable than transition states but may or may not be stable enough to isolate. 

An in situ infrared investigation has been conducted of the reduction of NO by CH4 over Co-ZSM-5. In the presence of O2, NO2 is formed via the oxidation of NO. Adsorbed NO2 then reacts with CH4. Nitrile species are observed and found to react very rapidly with NO2, and at a somewhat slower rate with NO and O2. The dynamics of the disappearance of CN species suggests that they are reactive intermediates, and that N2 and CO2 are produced by the reaction of CN species with NO2. While isocyanate species are also observed, these species are associated with A1 atoms in the zeolite lattice and do not act as reaction intermediates. A mechanism for NO reduction is proposed that explains why O2 facilitates the reduction of NO by CH4, and why NO facilitates the oxidation of CH4 by O2. 

The first point that must be established in an experimental study is that one is indeed dealing with a series combination of reactions instead of with some other complex reaction scheme. One technique that is particularly useful in efforts of this type is the introduction of a species that is thought to be a stable intermediate in the reaction sequence. Subsequent changes in the dynamic behavior of the reaction system (or lack thereof) can provide useful information about the character of the reactions involved. 

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