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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.
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 ...
A demonstration that how some well known 1,3-dipoles like ozone, nitro compounds and azides can be shown to have a resonance structure having 1,3 relationship between positive and negative formal charges. Known 1,3-dipoles are: Azides (RN 3) Ozone (O 3) Nitro compounds (RNO 2) Diazo compounds (R 2 CN 2) Some oxides. Azoxide compounds (RN(O)NR)
In another case, the stereoelectronic effect can result in an increased contribution of one resonance structure over another, which leads to further consequences in reactivity. For 1,4- benzoquinone monoxime, there are significant differences in the physical properties and reactivities between C2-C3 double bond and C5-C6 double bond.
Operationally, there are three ways in which alternative resonance structures may be generated: (1) from the LEWIS option, considering the Wiberg bond indices; (2) from the delocalization list; (3) specified by the user. [1] Below is an example of how NRT may generate a list of resonance structures.
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]
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
The 3-dimensional structure of the nitrilium ylide itself may also provide a clue as to the most appropriate resonance structure, with a linear R–C≡N–C unit supportive of the charge distribution indicated for resonance structures 1a & 1b and also consistent with the nomenclature nitrilium ylide.