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Contributing structures of the carbonate ion. In chemistry, resonance, also called mesomerism, is a way of describing bonding in certain molecules or polyatomic ions by the combination of several contributing structures (or forms, [1] also variously known as resonance structures or canonical structures) into a resonance hybrid (or hybrid structure) in valence bond theory.
In chemistry, the mesomeric effect (or resonance effect) is a property of substituents or functional groups in a chemical compound.It is defined as the polarity produced in the molecule by the interaction of two pi bonds or between a pi bond and lone pair of electrons present on an adjacent atom. [1]
A valence bond structure resembles a Lewis structure, but when a molecule cannot be fully represented by a single Lewis structure, multiple valence bond structures are used. Each of these VB structures represents a specific Lewis structure. This combination of valence bond structures is the main point of resonance theory.
Structurally the isomers can be distinguished by the geometry of the complex. In N-bonded cyanate complexes the M−NCO unit sometimes has a linear structure, but with O-bonded cyanate the M−O−C unit is bent. Thus, the silver cyanato complex, [Ag(NCO) 2] −, has a linear structure as shown by X-ray crystallography. [13]
Clar's rule states that for a benzenoid polycyclic aromatic hydrocarbon (i.e. one with only hexagonal rings), the resonance structure with the largest number of disjoint aromatic π-sextets is the most important to characterize its chemical and physical properties. Such a resonance structure is called a Clar structure. In other words, a ...
The negative charge that is left after deprotonation of the carboxyl group is delocalized between the two electronegative oxygen atoms in a resonance structure. If the R group is an electron-withdrawing group (such as –CF 3), the basicity of the carboxylate will be further weakened. [1]: 264–5
On the other hand, the nitrobenzene resonance structures have positive charges around the ring system: The nitro group can withdraw electron density through resonance. Attack occurs at the meta position, since the (partial) formal positive charges at the ortho and para positions indicate electron deficiency at these positions.
The azide functional group can be shown by two resonance structures. An organic azide is an organic compound that contains an azide (– N 3) functional group. [1] Because of the hazards associated with their use, few azides are used commercially although they exhibit interesting reactivity for researchers.