Equivalent Lewis structures

Nitrate ion is stabilized by electron delocalization which we can represent m terms of resonance between three equivalent Lewis structures... 

To deal with circumstances such as the bonding in ozone, the notion of resonance between Lewis structures was developed. According to the resonance concept, when more than one Lewis structure may be written for a molecule, a single structure is insufficient to describe it. Rather, the true structure has an electron distribution that is a hybrid of all the possible Lewis structures that can be written for the molecule. In the case of ozone, two equivalent Lewis structures may be written. We use a double-headed aiTow to represent resonance between these two Lewis structures. 

Step 6. Identify equivalent or near-equivalent Lewis structures... 

Which of these options is the best Lewis structure Actually, no single Lewis structure by itself is an accurate representation of NO3. Any single structure of the anion shows nitrate with one NDO double bond and two N— O single bonds. In Section 9 1, we show that single and double bonds between the same types of atoms have different lengths and different energies. In contrast, experiments show that the three nitrate N—O bonds are identical. To show that the nitrate N—O bonds are all alike, we use a composite of the three equivalent Lewis structures. These are traditionally called resonance structures. Resonance stmctures are connected by double-headed arrows to emphasize that a complete depiction requires all of them. 

The two candidates are equivalent Lewis structures, so the best depiction of H2 PO4 shows two resonance structures connected by a double-headed arrow. 

D. A conjugated molecule is a molecule with double bonds on adjacent atoms such as the molecule shown in A. Choice B and C give the definition of sigma and pi molecular orbitals. D is false because a resonance form is one of multiple equivalent Lewis structures, but these structures do not describe the actual state of the molecule. The anion will exist in a state between the two forms. 

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 ... 

We can elaborate this VB formulation for the cycloaddition by replacing the nearest-neighbour active-space AOs in VB structures 50 and 51 with Coulson-Fischer orbitals [34(b)]. Thus if a and b are now the singly-occupied carbon and oxygen AOs of HCNO, and c and d are the singly-occupied carbon AOs of HCCH, the c and d AOs in structure 50 can be replaced by the Coulson-Fischer MOs c + k d and d + k"c. In structure 51, a + Ad, b + Ac, c + K b and d + K"a can replace the a, b c and d AOs. Use of these orbitals permits additional canonical Lewis VB structures to be included in the equivalent Lewis structure resonance scheme. The mechanism can then accommodate some charge transfer between the HCNO and HCCH reactants. The more-flexible wavefunction of Eq.(13),... 

Formate anion is an example of an ion for which two equivalent Lewis structures (0 and ) can be drawn.The actual structure is a resonance hybrid of these two structures. Remember to use the double-headed arrow only between resonance structures. Never use equilibrium arrows ( .) between resonance structures. 

Equivalent Lewis structures contain the same numbers of single and multiple bonds. For example, the resonance structures for 03,... 

This is a resonance situation. Two equivalent Lewis structures can be drawn. The electronic structure of the molecule is not correctly represented by either resonance structure but by the average of the two. There are two equivalent N—O bonds, each one intermediate between a single and double bond. 

Benzene is conjugated, so we must use resonance and orbitals to describe its structure. The resonance description of benzene consists of two equivalent Lewis structures, each with three double bonds that alternate with three single bonds. 

Our drawing of the Lewis structure for ozone (O3) satisfied the octet rule for the central atom because we placed a double bond between it and one of the two end O atoms. In fact, we can put the double bond at either end of the molecule, as shown by these two equivalent Lewis structures ... 

Equivalent Lewis structures are called resonance forms. A double-headed arrow is used to indicate resonance. The actual molecule does not have a double bond on one bond and a single bond on the other. The molecular structure is in an average state between the resonance forms. 

Qualitative application of VB theory makes use of the concept of resonance to relate structural formulas to the description of molecular stmcture and electron distribution. The case of benzene is a familiar and striking example. Two equivalent Lewis structures can be drawn, but the actual structure is the average of these two resonance structures. The double-headed arrow is used to specify a resonance relationship. 

A set of equivalent Lewis structures can be drawn for benzene. Each structure differs only in the location of the three double bonds in the ring. Experimentally benzene does not have the chemical properties expected for molecules having any double bonds. 

Several equivalent Lewis structures can be drawn for some molecules, a concept called resonance... 

We can draw tv o more equivalent Lewis structures with the double bond betw een Cl and a different oxygen atom. 

We observe that in some cases more than one equivalent Lewis structure can be drawn for a molecule or polyatomic ion. The bonding description in such cases is a biend of two or more resonance structures. 

There is no reason for one of these Lewis structures to be dominant because they are equally valid representations of the molecule. The placement of the atoms in these two alternative but completely equivalent Lewis structures is the same, but the placement of the electrons is different. Lewis structures of this sort are called resonance structures. To describe the structure of ozone properly, we write both resonance structures and use a double-headed arrow to indicate that the real molecule is described by an average of the two ... 

As an additional example of resonance structures, consider the nitrate ion, N03, for which three equivalent Lewis structures can be drawn ... 

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