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Concept of Resonance

Many a time it is not possible to represent a molecule by a single valence bond structure that would correctly account for the properties of the substance. In such cases it is represented as a hybrid of two or more valence bond structures. The molecule is said to be a resonance hybrid of the various structures. By convention the different valence bond structures called the resonating structures or canonical structures are written down with a double headed arrow in between. Thus in the case of hydrogen molecule. [Pg.14]

The actual structure cannot be correctly depicted by any of the above 4 structures as it is a composite of these structures. The true structure is a hybrid of the above structures. The molecule has its own unique stable structure and the difficulty lies in representing the structure and not in the molecule. The resonance hybrid is more stable than any of the resonating structures. This extra stability of the actual molecule, is taken to be equal to the difference in energy between the actual molecule and the most stable of the resonating structures. This is called the resonance energy. This concept of resonance is of fundamental importance in valence bond treatment. [Pg.14]

The different resonating structures are written down keeping the following the following rules in mind  [Pg.14]

Each structure should have the same arrangement of atoms i.e., nuclear framework should be the same. Only the arrangement of electrons is different in the different structures. [Pg.14]

Each structure should have the same number of unpaired electrons. [Pg.15]


Write an essay of approximately 2000 words on the history and the various definitions of the concept of resonance, resonance energy, and aromaticity. [Pg.219]

Diazo coupling follows the rules of orientation of substituents in aromatic systems in accordance with the mechanism of electrophilic aromatic substitution and the concept of resonance. [Pg.428]

In Chapter 7, we used valence bond theory to explain bonding in molecules. It accounts, at least qualitatively, for the stability of the covalent bond in terms of the overlap of atomic orbitals. By invoking hybridization, valence bond theory can account for the molecular geometries predicted by electron-pair repulsion. Where Lewis structures are inadequate, as in S02, the concept of resonance allows us to explain the observed properties. [Pg.650]

We can use the concept of resonance to explain these characteristics of the benzene molecule. There are two Kekule structures with exactly the same energy they differ only in the positions of the double bonds. As a result of resonance... [Pg.194]

The convenience and usefulness of the concept of resonance in the discussion of chemical problems are so great as to make the disadvantage of the element of arbitrariness of little significance. Also, it must not be forgotten that the element of arbitrariness occurs in essentially the same way in the simple structure theory of organic chemistry as in the theory of resonance — there is the same use of idealized, hypothetical structural elements. In the resonance discussion of the benzene molecule the two Kekule structures have to be described as hypothetical it is not possible to synthesize molecules with one or the other of the two Kekule structures. In the same way, however, the concept of the carbon-carbon single bond is an idealization. The benzene molecule has its own structure, which cannot be exactly composed of structural elements from other molecules. The propane molecule also has its own structure, which cannot be composed of structural elements from other molecules — it is not possible to isolate a portion of the propane molecule, involving parts of two carbon atoms... [Pg.14]

It was pointed out in Chapter I that the selection of the primary structures for the discussion of any particular case of quantum-mechanical resonance is arbitrary, but that this arbitrariness (which has an analogue in the classical resonance phenomenon) does not impair the value of the concept of resonance. [Pg.247]

When we compare our present knowledge of structural chemistry with that of ten years ago and become cognizant of the extent to which clarity has been brought into this field of knowledge by the extensive application of the concept of resonance we are tempted to speculate about the future development of this concept and the nature of the further applications of it which may be made. [Pg.252]

In this book the discussion has been restricted to the structure of the normal states of molecules, with little reference to the great part of chemistry dealing with the mechanisms and rates of chemical reactions. It seems probable that the concept of resonance can be applied very effectively in this field. The activated complexes which represent intermediate stages in chemical reactions are, almost without exception, unstable molecules which resonate among several valence-bond structures. Thus, according to the theory of Lewis, Olson, and Polanyi, Walden inversion occurs in the hydrolysis of an alkyl halide by the following mechanism ... [Pg.253]

Recall that we used the analogy of a nectarine (being a hybrid between a peach and plum) to explain the concept of resonance. Now, imagine that we create a new type of fruit that is a hybrid between three fruits a peach, a plum, and a kiwi. Suppose that the hybrid fruit that we produce has the following character 65% peach character, 34% plum character, and 1% kiwi character. This hybrid fruit will look almost exactly like a nectarine, because the amount of kiwi character is too small to have an effect on the nature of the resulting hybrid. Even though this fruit is actually a hybrid of three fruits, nevertheless it will look like a hybrid of only two fruits— because the kiwi character is insignificant. ... [Pg.47]

There are no alternative ways of positioning electrons around the HI molecule. If you missed this question, refer to your textbook on the concept of resonance. [Pg.104]

Note that the equation (74) for k+ can be recast in terms of the probability P-> for the system to continue from the QIC towards products, namely, P—> = k + / (k - + k +), so that k+ = k + P->. This equation can be further worked out in order to include the concept of resonance in a more direct way. To get at the desired result, one has to calculate the rate at which Ci(t) is changing. The differential equation fulfilled by this coefficient can be obtained by using an adiabatic coupling method [47] that, in the limit r ->0 it is given by... [Pg.328]

Aromatic compounds and their reactions are a big part of any Organic 11 course. We introduce you to the aromatic family, including the heterocyclic branch, in Chapter 6. (You may want to brush up on the concept of resonance beforehand.) Then in Chapters 7 and 8, you find out more than you ever wanted to know about aromatic substitution reactions, starring electrophiles and nucleophiles. [Pg.15]

Everyone receives an introduction to the basic concepts of resonance in Organic Chemistry I. Organic Chemistry II requires an extension of the basic rules of resonance to other systems. In addition to constructing reasonable resonance structures, you also need to understand which structures cire more stable. [Pg.56]

In the following sections of this chapter there are given, after an introductory survey of the types of chemical bonds, discussions of the concept of resonance and of the nature of the one-electron bond and the electron-pair bond. [Pg.5]

There is one fundamental principle of quantum mechanics that finds expression in most of the chemical applications of the theory to problems dealing with the normal states of molecules. This is the principle that underlies the concept of resonance. [Pg.10]

The concept of resonance was introduced into quantum mechanics by Heisenberg16 in connection with the discussion of the quantum states of the helium atom. He pointed out that a quantum-mechanical treatment somewhat analogous to the classical treatment of a system of resonating coupled harmonic oscillators can be applied to many systems. The resonance phenomenon of classical mechanics is observed, for example, for a system of two tuning forks with the same characteristic frequency of oscillation and attached to a common base, hich... [Pg.12]

The discussion in Section 1-3 about the element of arbitrariness in the concept of resonance may be recalled at this point with reference to the nitrous oxide molecule and the other molecules that are described in this chapter as resonating among several valence-bond structures. It is not necessary that the structures A, B, and C be used as the basis of discussion of the nitrous oxide molecule. We might say instead that the molecule cannot be satisfactorily represented by any single valence-bond structure, and abandon the effort to correlate its structure and properties with those of other molecules. By using valence-bond structures as the basis for discussion, howrever, with the aid of the concept of resonance, we are able to account for the properties of the molecule in terms of those of other molecules in a straightforward and simple way. It is for this practical reason that we find it convenient to speak of the resonance of molecules among several electronic structures. [Pg.186]

The concept of resonance provides an obvious explanation of some of the characteristic properties of the carboxyl group, the most striking of which is its acid strength. If the electronic structure of a carboxylic... [Pg.276]

When this kind of interaction occurs between vibrational states instead of electronic states it is called Fermi resonance we shall discuss this later (Sect. 10.8). In fact, the whole qualitative concept of resonance stabilization as used in the valence bond theory is just the same principle in still another guise. [Pg.180]


See other pages where Concept of Resonance is mentioned: [Pg.170]    [Pg.246]    [Pg.246]    [Pg.252]    [Pg.31]    [Pg.200]    [Pg.241]    [Pg.424]    [Pg.11]    [Pg.217]    [Pg.46]    [Pg.211]    [Pg.83]    [Pg.172]    [Pg.180]    [Pg.389]    [Pg.11]    [Pg.13]    [Pg.13]    [Pg.13]    [Pg.188]    [Pg.192]    [Pg.219]    [Pg.563]    [Pg.569]    [Pg.569]    [Pg.569]   


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