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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.
3, X = F, Br, Cl, I) via a molecular orbital (MO) description, building on the concept of the "half-bond" introduced by Rundle in 1947. [ 4 ] [ 5 ] In this model, two of the four electrons occupy an all in-phase bonding MO, while the other two occupy a non-bonding MO, leading to an overall bond order of 0.5 between adjacent atoms (see Molecular ...
The NBOs for a resonance structure formula can then be, subsequently, calculated from the CHOOSE option. 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]
One of the simplest member is C(CN) 4 (tetracyanomethane, also known as carbon tetracyanide). Organic chemists often refer to cyanides as nitriles. In general, cyanide is an electronegative substituent. Thus, for example, cyanide-substituted carboxylic acids tend to be stronger than the parents.
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 ...
4-Cyano-4'-pentylbiphenyl is a commonly used nematic liquid crystal with the chemical formula C 18 H 19 N. It frequently goes by the common name 5CB. 5CB was first synthesized by George William Gray, Ken Harrison, and J.A. Nash at the University of Hull in 1972 and at the time it was the first member of the cyanobiphenyls.
In 1,2-difluoroethane, despite the steric clash, the preferred conformation is the gauche one because σ(C–H) is a good donor and σ*(C–F) is a good acceptor and the stereoelectronic effect (σ(C–H) → σ*(C–F)) requires the energy minimum to be gauche instead of anti.
Allylic shifts become the dominant reaction pathway when there is substantial resistance to a normal (non-allylic) substitution. For nucleophilic substitution, such resistance is known when there is substantial steric hindrance at or around the leaving group, or if there is a geminal substituent destabilizing an accumulation of positive charge.