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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.
The anthracene molecule allows three resonance structures, each with a circle in one ring and two sets of double bonds in the other two. Following rule 4 above, anthracene is better described by a superposition of these three equivalent structures, and an arrow is drawn to indicate the presence of a migrating π-sextet.
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] This change in electron arrangement results in the formation of resonance structures that hybridize into the molecule's true structure. The pi electrons then move away from or ...
When comparing resonance structures for the same molecule, usually those with the fewest formal charges contribute more to the overall resonance hybrid. When formal charges are necessary, resonance structures that have negative charges on the more electronegative elements and positive charges on the less electronegative elements are favored.
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.
Although the electronic structure according to valence bond theory can be written as H−N=C=O, the vibrational spectrum has a band at 2268.8 cm −1 in the gas phase, which some say indicates a carbon–nitrogen triple bond. [10] [11] If so, then the canonical form H−N + ≡C−O − is the major resonance structure.
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]
Diazo compounds have two main Lewis structures in resonance: R 2 >C-–N + ≡N and R 2 >CH=N + =N-. In organic chemistry, the diazo group is an organic moiety consisting of two linked nitrogen atoms at the terminal position.