Hybrid of resonance structures

When 1-hydroxymelatonin (19) is treated with acid, removal of its 1-hydroxy group leaves an indolyl cation (a hybrid of resonance structures 254,168, and so on) as shown in Scheme 37. If there is a subsequent intramolecular nucleophilic attack by the Ab-nitrogen atom on the side chain or if an intermolecular attack by suitable nucleophiles occurs on this intermediate cation, the birth of a new type of product can be expected. 

The reactivity of triketone orthocarbonate 403 is very interesting. The most hindered carbonyl group, i, e. C- = 0, is the most reactive one towards nucleophilic addition. This behavior can be rationalized by the fact that the C1 - Cg bond is parallel to the v system of the carbonyl group at C-8. Indeed, this compound can be viewed as the hybrid of resonance structures 403<- 404. 

Resonance is a stabilizing factor. The hybrid of resonance structures (resonance hybrid) is usually more stable than any of its contributing forms by an amount called the resonance energy. The closer the stability of the contributing forms the greater the resonance energy of the hybrid. 

The total symmetry of the molecule is D2h and therefore one cannot have point group degenerate states. The aceidentally degenerate states represented above have C2v symmetry. The direet product C2v Cg recovers properly the full symmetry of the system. Once more it is correct to describe these excited states as hybrids of resonance (structures c and d). 

The structure of nitrogen dioxide contains an unpaired (odd) electron and the molecule is consequently paramagnetic. The odd electron is not localised on any atom and the structure can be best represented as a resonance hybrid of the structures ... 

In valence bond terms the pyrazine ring may be represented as a resonance hybrid of a number of canonical structures (e.g. 1-4), with charge separated structures such as (3) contributing significantly, as evidenced by the polar character of the C=N bond in a number of reactions. The fusion of one or two benzene rings in quinoxaline (5) and phenazine (6) clearly increases the number of resonance structures which are available to these systems. 

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 ... 

Each of these tautomers in its normal state is represented not by the conventional valence-bond structure shown above, but by a resonance hybrid of this structure and others. For tautomer A, with the hydrogen atom attached to the nitrogen atom 1, the principal resonance is between structures A I and A II, with A I the more important smaller contributions are made also by other structures such as A III. Similar resonance occurs for tautomer B. Thus for both tautomers the principal resonance... 

A similar concept exists when comparing resonance structures. One compound might have three resonance structures, but all three resonance structures might not contribute equally to the overall resonance hybrid. One resonance structure might be the major contributor (like the peach), while another resonance structure might be insignificant (like the kiwi). In order to understand the true nature of the compound, we must be able to compare the resonance structures and determine which structures are major contributors and which structures are not significant. 

The structure of diazomethane is a resonance hybrid of three structures ... 

Since the a-C atoms in C-nitro compounds are sp3 hybridized, whereas these atoms in nitronates are sp2 hybridized, the signals for both the a-C atom and the protons bonded to this atom are shifted in nitronates to lower field. However, all of the above mentioned signals in the NMR spectra of nitronates RR,C=N(0)0X do appear at higher field than the corresponding signals for analogous oximino derivatives RR,C=N-0- due to the contribution of resonance structures A and B shown in Chart 3.6. 

You have read earlier that aniline is a resonance hybrid of five structures. Where do you find the maximum electron density In these structures Ortho- and para-posltlons to the -NHg group become centres of high electron density. Thus -NH group Is ortho and para directing and a powerful activating group. 

Generally, the diazo carbon is characterized by a large upheld shift, as compared with the usual range for a normal sp hybridized carbon in the parent ring. These large shifts might reflect substantial contributions of resonance structures of type 3a or 3d [78JA4974]. This effect is not surpris-... 

For purposes of org nomenclature the terms azido" and "triazo are used syn-omously in the literature. The aryl azides are often called in German diazoimides. Aliphatic diazo compds contain the group = CN2, represented as a resonance hybrid of the structure... 

The molecular complex formed by the interaction of donor and acceptor can be considered as a resonance hybrid of two structures one a no-bond structure (DA) in which the two molecules are bound together only by van der Waals forces and the other in which an ionic bond exists between the donor and the acceptor (D+ — A ). The main contribution to the ground state is from the no-bond structure and the wave function is represented as... 

Pyridazine, one of the three possible isomeric diazines, is assumed to be a planar six-membered ring and is represented as a resonance hybrid of two structures (la) and (lb) with a greater contribution from the canonical structure (la). 

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 stabilization energy of the carboxylate anion is substantially greater than that of the acid, because the anion is a resonance hybrid of two energetically equivalent structures, 2a and 2b, whereas the acid is represented by a hybrid of nonequivalent structures, 1a through 1c ... 

Resonance hybrid. A molecular structure that is a hybrid of two structures that differ in the locations of some of the electrons. For example, the benzene ring can be drawn in two ways, with double bonds in different positions. The actual structure of benzene is a blending of these two equivalent structures. 

Ozonium Ion (H03+). Ozone is a resonance hybrid of canonical structures 50a-50d.135 Ozone does in fact act as a 1,3-dipole—that is, either as an electrophile or a nucleophile. The electrophilic nature of ozone has been recognized for a long time in its reactions with alkenes, alkynes, arenes, amines, phosphines,... 

---