Drawing Resonance Forms

Se02, like SO2, has two resonance forms. Draw their Lewis structures. 

Draw a portion of the structure of a fullerene nanotube molecule, say, several hexagons, using one resonance form. Draw another resonance form. Describe the bonding at the carbon atoms in terms of hybrid orbitals. 

When first dealing with resonance forms, it s useful to have a set of guidelines that describe how to draw and interpret them. 

Thomson Click Organic Interactive to use an online palette to practice drawing resonance forms. 

Look back at the resonance forms of the acetate ion and the acetone anion shown in the previous section. The pattern seen there is a common one that leads to a useful technique for drawing resonance forms. In general, any three-atom grouping with a p orbital on each atom has two resonance forms. 

Draw three resonance forms for the carbonate ion, C032 ... 

Draw three resonance forms for the pentadienyl radical. A radical is a substance that contains a single, unpaired electron in one of its orbitals, denoted by a dot ( )-... 

Problem 2.10 1 Draw the indicated number of resonance forms for each of the following species ... 

Electrophilic addition of HCJ to a conjugated diene involves the formation of allylic carbocation intermediates. Thus, the first step is to protonate the two ends of the diene and draw the resonance forms of the two allylic carbocations that result. Then... 

Chemists sometimes represent the two benzene resonance forms by using a circle to indicate the equivalence of the carbon-carbon bonds. This hind of representation has to be used carefully, however, because it doesn t indicate the number of tt 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 tt electrons this way but must be aware of the limitations of the drawings. 

Azulene, a beautiful blue hydrocarbon, is an isomer of naphthalene. Is azulene aromatic Draw a second resonance form of azulene in addition to that shown. 

Problem 24.24 Indole reacts with electrophiles at C3 rather than at C2. Draw resonance forms of the intermediate cations resulting from reaction at C2 and C3, and explain the observed results. 

Draw resonance forms for the purple anion obtained by reaction of ninhydrin with an n-amino acid (Problem 26.53). 

Draw the most important Lewis structure for each of the following molecules. Show all lone pairs and formal charges. Draw all equivalent resonance forms, (a) HONCO (b) H2CSO (c) H2CNN (d) ONCN. 

Sometimes when writing the Lewis structure of a species, we may draw more than one possible correct Lewis structure for a molecule. The nitrate ion, N03 , is a good example. The structures that we write for this polyatomic anion differ in which oxygen has a double bond to the nitrogen. None of these three truly represents the actual structure of the nitrate ion—it is an average of all three of these Lewis structures. We use resonance theory to describe this situation. Resonance occurs when more than one Lewis structure (without moving atoms) is possible for a molecule. The individual structures are called resonance structures (or forms) and are written with a two-headed arrow (<- ) between them. The three resonance forms of the nitrate ion are ... 

Ozone, O3, is an essential molecule in the ozone layer. It filters out some of the UV radiation that would otherwise destroy life on Earth. At ground level, ozone is a component in photochemical smog. Draw the Lewis structure for ozone, and indicate whether or not ozone is polar. Can ozone exist in resonance forms ... 

There are two ways of representing this, according to which resonance form of the enolate anion is used. Although the preferred resonance form (charge located on the oxygen atom) should be used as the nucleophile, because carbon is acting as the nucleophile and a new C-Br bond is formed, the less-favoured resonance form is frequently employed in mechanistic pathways. This makes mechanism drawing rather easier, but is technically incorrect. 

Both the C—C bond lengths [(I) - 149.7 pm (2) = 147.6 pm] and the bending of the substituents out of the plane [(11 = 32.2° (2) = 38.4°] are nearly the same. Although we can draw an alternative resonance form for the nickel complex, the bonding model shown is the only one applicable to Ihe oxide. In view of the strong structural similarities, we can feel justified in using the cyclic structure us nn approximation for certain complexes as welL... 

There are two possible shapes for diimide, H-N=N H. Draw both, and tell if they are resonance forms. 

Draw three resonance forms for naphthalene, showing the positions of the double bonds. 

Draw resonance forms of an amino acid that explain why the dihedral angle co is almost always either 0 or 180°. 

The peak at mlz 93 is rationalized in Scheme 1.10 as a structure of formula C7H9+ formed by double bond isomerization (resulting in increased conjugation), followed by allylic cleavage. The ion at mlz 93 has at least two important resonance forms that contribute to its stability. As an exercise, the student is encouraged to draw them. 

These two equivalent Lewis structures are called resonance forms. In describing the structure of ozone, we draw both structures and say that ozone is represented by an average of the two structures ... 

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