Reaction arrows

The redox and proton transfer reactions undergone by the flavin prosthetic group are summarized in Scheme 5.2. The vertical reactions are oxidations by Q regenerating P. From the standard potential values (V vs. SCE) of the four flavin redox couples that are involved in Scheme 5.2 and those of the mediators (Table 5.1), all four oxidation steps may be regarded as irreversible. The horizontal reactions are deprotonations by the bases present in the buffer. From the pA values of the various flavin acid-base couples indicated in Scheme 5.2 (over or below the horizontal arrows), reactions H2 and H4 may be regarded as irreversible and reactions HI and... 

At the RHF level of theory, which uses a wavefunction that is relatively straightforward to interpret, the subtle differences between the half- and full-arrow reaction schemes would remain well-hidden within the doubly-occupied, usually delocalized orbitals. While it can be argued that the application of an orbital localization procedure could produce a semblance of the SC description for the 1,3-dipolar cycloaddition of fulminic acid to ethyne, the double-occupancy restriction makes it impossible to obtain the analogue of a half-arrow SC mechanism using an RHF wavefunction. 

Many types of cirrows cire used in organic chemistry, and each of them conveys information about the particular reaction. These arrows include the resonance arrow, equilibrium arrow, reaction arrow, double-headed arrow, and singleheaded cirrow. 

Fig. 14.4. Chemo-mechanical and mechano-chemical energy conversion through a series of fitting and unfitting processes. Blue arrows, reaction driven by free energy of hydrolysis pink arrows, reverse reactions driven by an external force...

Table 5.3. 1 Difference fractionation factors, e= product- Sre ctant, for important equilibrium (equations with two-way arrows) and kinetic (one-way arrows) reactions among the elements H, C, 0, and N Equilibrium fractionation factors are for 20 °C. Kinetic fractionation factors are approximate as they vary in the marine environment. ...

Figure 12.4. Pathways in the metabolism of L-dopa (1) and its major decarboxylated product dopamine (2). Major (heavy arrows) and minor (light arrows) reactions are indicated. AD, aldehyde dehydrogenase AAD, aromatic L-amino acid decarboxylase COMT, catechol-O-methyltransferase DH, dopamine jS-hydroxylase MAO, monoamine oxidase PNMT, phenylethanolamine-N-methyl-transferase.

Fig. 13. Metabolism scheme of sialic acids. Anabolic (solid arrow) and catabolic (dashed arrow) reactions are indicated. For literature see the text. Enzymes 1, CMP-sialate synthase (EC 2.7.7.43) 2, sialyltransferases (EC 2.4.99.1.) 3, CMP-Neu5Ac hydroxylase (EC 1.14.99.18) 4, acetyl-CoA sialate 4-0-acetyltransferase (EC 2.3.1.44) 5, acetyl-CoA sialate 7(9)-0-acetyltransferase (EC 2.3.1.45) 6,. S-adenosyl-L-methionine sialate 8-O-methyltransferase (proposed EC 2.1.1.78) 7, sialate 4- or 9-0-acetylesterases (EC 3.1.1.53) 8, sialidase (EC 3.2.1.18) 9, sialate-pyruvate lyase (aldolase EC 4.1.3.3). Both Neu5Ac and Neu5Gc can be O-acetylated by the two O-acetyltransferases. There may also exist a sulfotransferase, since sulfated sialic acids have been found in e.g. echinoderms [13,577]. ( ), Sialic-acid-accepting nascent glycoconjugate.

Figure 5-1 The Central Dogma as formulated in 1958 with probable (solid arrows) and possible (broken arrows) reactions as indicated (adapted from [lb]).

Fig. 1. Schematic drawing of the charge (dashed arrows) and discharge (solid arrows) reactions of a Ni-MH battery (Iwakura and Matsuoka 1990).

The anisotropy of the product rotational state distribution, or the polarization of the rotational angular momentum, is most conveniently parametrized tluough multipole moments of the distribution [45]. Odd multipoles, such as the dipole, describe the orientation of the angidar momentum /, i.e. which way the tips of the / vectors preferentially point. Even multipoles, such as the quadnipole, describe the aligmnent of /, i.e. the spatial distribution of the / vectors, regarded as a collection of double-headed arrows. Orr-Ewing and Zare [47] have discussed in detail the measurement of orientation and aligmnent in products of chemical reactions and what can be learned about the reaction dynamics from these measurements. 

Figure C3.3.10. A schematic energy-level diagram for a molecule capable of undergoing unimolecular reaction above tlie energy depicted as tlie reaction barrier. Arrows to tlie right indicate reaction (collision-free) at a rate kg tliat depends on tlie energy E. Down arrows represent collisional redistribution of tlie hot molecules botli above and below tlie reaction barrier.

Here, the reaction proceeds effectively to completion (HCl) is very large relative to (Hj) and (Clj) and hence (and K ) are also large. In these circumstances the reverse arrow is usually omitted. 

Let us consider the formation of sodium chloride from its elements. An energy (enthalpy) diagram (called a Born-Haber cycle) for the reaction of sodium and chlorine is given in Figure 3.7. (As in the energy diagram for the formation of hydrogen chloride, an upward arrow represents an endothermic process and a downward arrow an exothermic process.)... 

Drawing-, text-, and structure-input tools are provided that enable easy generation of flow charts, textual annotations or labels, structures, or reaction schemes. It is also possible to select different representation styles for bond types, ring sizes, molecular orbitals, and reaction arrows. The structure diagrams can be verified according to free valences or atom labels. Properties such as molecular... 

The reaction field method. The shaded arrow represents the mm of the dipoles of the other molecules within sphere. 

Because the intermediates Me and MeiCOH are pretty rmlikely species and they would have to be intermediates in the real reaction too We have already found the first way to recognise a good disconnection it has a reasonable mechanism. Choose a discormection for this molecule, target molecule 3 (TM 3) breaking bond a or b. Draw the arrow and the intermediates. 

Antithetical connections (the reversal of synthetic cleavages) and rearrangements are indicated by a con or rcarr on the double-lined arrow. Here it is always practical to draw right away the reagents instead of synthons. A plausible reaction mechanism may, of course, always be indicated. 

In Section 1 9 we introduced curved arrows as a tool to systematically generate resonance structures by moving electrons The mam use of curved arrows however is to show the bonding changes that take place in chemical reactions The acid-base reactions to be discussed in Sections 1 12-1 17 furnish numer ous examples of this and deserve some preliminary comment... 

Potassium hydride (KH) is a source of the strongly basic hydride ion ( H ) Using curved arrows to track electron movement write an equation for the reaction of hydride ion with water What is the conjugate acid of hydride lon ... 

Wnte an equation for the Brpnsted acid-base reaction that occurs when each of the fol lowing acids reacts with water Show all unshared electron pairs and formal charges and use curved arrows to track electron movement... 

Assuming that the rate determining step in the reaction of cyclohexanol with hydrogen bro mide to give cyclohexyl bromide is unimolecular write an equation for this step Use curved arrows to show the flow of electrons... 

Use curved arrows to show the bonding changes in the reaction of CIS 4 tert butylcyclohexyl bromide with potassium tert butoxide Be sure your drawing correctly represents the spatial relationship between the leaving group and the proton that is lost... 

It IS convenient in synthetic transformations involving more than one step simply to list all the reagents with a single arrow Individual syn thetic steps are indicated by number Numbering the in dividual steps is essential so as to avoid the implication that everything is added to the reaction mixture at the same time... 

A standard method for prepanng sodium cyclopentadienide (CsHsNa) is by the reaction of cyclopentadiene with a solution of NaNH2 in liquid ammonia Write a net ionic equation for this reaction identify the acid and the base and use curved arrows to track the flow of electrons... 

Write the equation for the reaction of 1 hexyne with ethyl magnesium bromide as if it involved ethyl anion (CH3CH2 ) instead of CH3CH2MgBr and use curved arrows to represent the flow of electrons j... 

A method for the generation of benzyne involves heating the diazonium salt from o aminobenzoic acid (benzenediazonium 2 carboxylate) Using curved arrows show how this sub stance forms benzyne What two inorganic compounds are formed in this reaction" ... 

Using this insight Berthollet reasoned that the reaction is reversible, and that the relative amounts of reactants and products determine the direction in which the reaction occurs, and the final composition of the reaction mixture. We recognize a reaction s ability to move in both directions by using a double arrow when writing the reaction. 

By convention, species to the left of the arrows are called reactants, and those on the right side of the arrows are called products. As Berthollet discovered, writing a reaction in this fashion does not guarantee that the reaction of A and B to produce C and D is favorable. Depending on initial conditions, the reaction may move to the left, to the right, or be in a state of equilibrium. Understanding the factors that determine the final position of a reaction is one of the goals of chemical thermodynamics. 

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