Curved arrow formalism

The curved-arrow formalism is universally used for keeping track of the flow of electrons in reactions. We have also used this device (in Section 1-9, for example) to keep track of electrons in resonance structures as we imagined their flow in going from one resonance structure to another. Remember that electrons do not flow in resonance structures they are simply delocalized. Still, the curved-arrow formalism helps our minds flow from one resonance structure to another. We will find ourselves constantly using these (red) curved arrows to keep track of electrons, both as reactants change to products and as we imagine additional resonance structures of a hybrid. 

PROBLEM 18.4 Represent the reaction of chlorine with each of the enol forms of 2-butanone (see Problem 18.3) according to the curved arrow formalism just described. 

Explain the different products of the following two reactions by considering the mechanism by which each reaction proceeds. As part of your explanation, use the curved arrow formalism to draw a mechanism for each reaction. 

In a reaction of HCl and ammonia, identify the electron-donating atom of the hase and draw the reaction using the curved arrow formalism, giving the products of the reaction. 

Problem 1L7. Using the curved arrow formalism, write a suitable pathway from a-santonin to santonic acid and then to santonide (Woodward, 1950). Answered. (Note the details of the mechanism are suggestions )... 

Problem 11.11. Examine the chemistry of Scheme 11.78. Describe (with suitable curved arrow formalism) what is happening in each step. 

Learn how to use the curved arrow formalism to push pairs of electrons in writing resonance forms and in sketching electron flow in chemical reactions. 

Both of these ways of producing " CH3 and CH3 involve the concept of breaking a carbon-hydrogen bond in unsymmetrical fashion, a process known as heterolytic bond cleavage (p. 37 and Fig. 2.13). Remember the curved arrow formalism—the red arrows of Figure 2.13 move the pair of electrons in the carbon—hydrogen bond to the hydrogen or to the carbon. 

In Figure 2.60, the curved arrow formalism shows the electron flow as the new bond is formed in this illustrated nucleophile-electrophile (Lewis base-Lewis acid) reaction. 

FIGURE 2.60 The curved arrow formalism for the formation of methyl chloride from the methyl cation (Lewis acid) and a chloride ion (Lewis base). 

PROBLEM 2.65 Show the curved arrow formalism (electron pushing or arrow pushing) for the protonation of water in sulfuric acid (HOSO2OH = H2SO4). 

In looking at Figure 3.71, don t forget the curved arrow formalism (p. 23). The double-barbed arrows track the movements of pairs of electrons. The color-coding should help. Notice also the red and green equilibrium arrows. The different lengths reflect the exothermicity or endothermicity of each step. The first step is endothermic, and the second is exothermic. 

We have seen it before, as early as Chapter 1, but in this chapter the curved arrow formalism becomes more important than ever. If you are at all uncertain of your ability to push electrons with arrows, now is definitely the time to sofidify this skill. In the arrow formalism convention, arrows flow from electrons. But be carefiil about violating the mles of valence arrows either displace another pair of electrons or fiU a hole —an empty orbital. 

FIGURE 7.3 Two demonstrations of the application of the curved arrow formalism. We will see many other examples. 

The curved arrow formalism is used extensively in this chapter. This bookkeeping device is extremely useful in keeping... 

Arrow formalism, curved arrow formalism, or electron pushing (Section 1.4) A mapping device for chemical reactions. The electron pairs (lone pairs or bond pairs) are pushed using curved arrows that show the bonds that are forming and breaking in the reaction. 

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