Resonance hybrid drawing

PROBLEM 19.8 For those molecules in Table 19.6 that must be described as resonance hybrids, draw electron-dot resonance structures, assign formal charges, and indicate which resonance structure(s) is (are) most important. In addition, indicate which of the molecules in Table 19.6 are paramagnetic. 

For each ion in Problem 1.47 draw the resonance hybrid. Draw all reasonable resonance structures for each species. 

Does your transition state drawing look more like a sing Lewis structure or a resonance hybrid If the latter, whi resonance contributors must you combine to generate a of the features of this hybrid ... 

In what ratio would you expect the three products to be formed if o-xylene is a resonance hybrid of two structures The actual ratio found was 3 parts glyoxal, 1 part 2,3-butanedione, and 2 parts pyruvaldehyde. What conclusions can you draw about the structure of o-xylene ... 

Draw the Lewis structures that contribute to the resonance hybrid of nitryl chloride, CINQ, (N is the central atom). 

Benzene, CgHg, is a common industrial solvent. The benzene molecule is based on a ring of covalently bonded Ccirbon atoms. Draw two acceptable Lewis structures for benzene. Based on the structures, describe a likely resonance hybrid structure for benzene. 

The method that commonly is used is to draw a set of structures, each of which represents a reasonable way in which the electrons (usually in p orbitals) could be paired. If more than one such structure can be written, the actual molecule, ion, or radical will have properties corresponding to some hybrid of these structures. A double-headed arrow <—> is written between the structures that we consider to contribute to the hybrid. For example, the two Kekule forms are two possible electron-pairing schemes or valence-bond structures that could contribute to the resonance hybrid of benzene ... 

The nitrate ion, N03, has three equivalent oxygen atoms, and its electronic structure is a resonance hybrid of three electron-dot structures. Draw them. 

The N2O5 molecule has six N-O a bonds and two N 0 17 bonds, but has no N-N bonds and no 0-0 bonds. Draw eight resonance structures for N2O5, and assign formal charges to the atoms in each. Which resonance structures make the more important contributions to the resonance hybrid ... 

Why does the adamantyl compound shown below behave more like a ketone than an amide Hint Draw the corresponding resonance hybrid.)... 

Draw the electron-dot formulas that show all important contributors to a resonance hybrid and show their electronic relationship using curved arrows. 

Draw conventional structures for the contributors to the resonance hybrid of an allyl cation. 

Draw the structures of the main contributors to the benzenonium ion resonance hybrid. 

Draw the important contributors to the resonance hybrid for an aromatic amine. 

Draw the important resonance structures for aniline. Use the curved arrow convention to show how the electrons are moved to create each new resonance structure. Discuss the relative contribution of each to the resonance hybrid and the overall resonance stabilization of the compound. 

Some compounds structures are not adequately represented by a single Lewis structure. When two or more valence-bond structures are possible, differing only in the placement of electrons, the molecule will usually show characteristics of both structures. The different structures are called resonance structures or resonance forms because they are not different compounds, just different ways of drawing the same compound. The actual molecule is said to be a resonance hybrid of its resonance forms. In Solved Problem l-l(d) we saw that the ion [H2CNH2]"1" might be represented by either of the following resonance forms ... 

This empirical yardstick draws a boundary between [2 + 2] cycloadditions that occur through essentially diradical or essentially zwitterionic tetramethylenes the resonance hybrid view which encompasses a continuous range of more or less dipolar intermediates is neglected in favor of a more decisive either/or discrimination. 

How can we draw a hybrid, which has delocalized electron density First, we must determine what is different in the resonance structures. Two differences commonly seen are the position ol a multiple bond and the site of a charge. The anion (HCONH) illustrates two conventions foi drawing resonance hybrids. 

Draw four additional resonance structures for the following cation. Then draw the resonance hybrid. 

Diels-Alder reaction of a monosubstituted diene (such as CH2=CH-CH=CHOCH3) with a monosubstituted dienophile (such as CH2=CHCH0) gives a mixture of products, but the 1,2-disubstituted product often predominates. Draw the resonance hybrid for each reactant and use the charge distribution of the hybrids to explain why the 1,2-disubstituted product is the major product. 

First, draw a structure, 1-16, for naphthalene that shows alternating single and double bonds around the periphery. This is one of the resonance structures that contributes to the character of delocalized naphthalene, a resonance hybrid. 

Often it is useful to draw resonance forms for proposed intermediates because their existence is an indication of stability, which represents a driving force for the reaction. Removal of a proton from the OH group of the resonance hybrid of 2-9 and 2-10 is unlikely because bromide ion is an even weaker base than DMSO (the pK of HBr is -9). Therefore, it is expected that ring closure, by nucleophilic reaction with the cation, takes place before removal of the proton. 

The overlap of the p orbitals in both directions, and the resulting participation of each electron in two bonds, is equivalent to our earlier description of the allyl radical as a resonance hybrid of two structures. These two methods of representation, the drawing of several resonance structures and the drawing of an electron cloud, are merely our crude attempts to convey by means of pictures the idea that a given pair of electrons may serve to bind together more than two nuclei. It is this... 

We see that the alcohol and alkoxide ion are each represented satisfactorily by a single structure. However, we can draw two reasonable structures (I and II) for the carboxylic acid and two reasonable structures (III and IV) for the carboxy-late anion. Both acid and anion are resonance hybrids. But is resonance equally... 

Another molecule that has resonance structures is sulfur dioxide, SO2, shown in Figure 13. Sulfur dioxide released into the atmosphere is partly responsible for acid precipitation. The actual structure of SO2 is an average, or a resonance hybrid, of the two structures. Although you draw the structures as if the bonds change places again and again, the bonds do not in fact move back and forth. The actual bonding is a mixture of the two extremes represented by each of the Lewis structures. 

The best way to think about resonance forms is to realize that a molecule like nitromethane is no different from any other. Nitromethane doesn t jump hack and forth between two resonance forms, spending part of its time looking like one and the rest of its time looking like the other. Rather, nitromethane has a single unchanging structure that is a resonance hybrid of the two individual forms and has characteristics of both. The only problem with nitromethane is that we can t draw it accurately using a familiar Kekule line-bond structure. Line-bond structures just don t work well for resonance hybrids. The difficulty, however, lies with the representation of nitromethane on paper, not with nitromethane itself. 

Resonance theory (Sections 2.4-2.5) accounts for the stability and properties of benzene by describing it as a resonance hybrid of two equivalea forms. Neither form is correct by itself the true structure of benzene is somewhere in between the two resonance forms but is impossible to draw with our usual conventions. Many chemists therefore represent benzene by drawing it with a circle inside to indicate the equivalence of the carbon-carbon bonds. This kind of representation has to be used carefully, however, because it doesn t indicate the number of w electrons in the ring. (How many electrons does a circle represent ) In this book, benzene and other aromatic compounds will be represented by a single line-bond structure. We ll be able to keep count of jr electrons this way, but we must be aware of the limii tions of the drawing. . 

We can t really draw an accurate representation of the carboxylate resonance hybrid using Kekule structures, but an orbital picture of acetate if" makes it clear that the carbon-oxygen bonds are equivalent and that ea is intermediate between a single and a double bond (Figure 20.2). The p orbital on the carboxylate carbon atom overlaps equally well with p orbitals on both oxygens, and the four p electrons are delocalized throughout the three-atom ir electron system. 

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