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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.
Aliphatic alcohols give azides via a variant of the Mitsunobu reaction, with the use of hydrazoic acid. [1] Hydrazines may also form azides by reaction with sodium nitrite: [16] Alcohols can be converted into azides in one step using 2-azido-1,3-dimethylimidazolinium hexafluorophosphate (ADMP) [17] or under Mitsunobu conditions [18] with diphenylphosphoryl azide (DPPA).
The mesomeric effect however, deals with restructuring and occurs when the electron pair of the substituents shift around. The inductive effect only acts on alpha carbons, while the mesomeric utilizes pi bonds between atoms. [4] While these two paths often lead to the similar molecules and resonance structures, the mechanism is different.
Bis(triphenylphosphine)iminium chloride, a common iminophosphorane, is prepared in two steps from triphenylphosphine Ph 3 P: [2] Ph 3 P + Cl 2 → Ph 3 PCl 2 2 Ph 3 PCl 2 + NH 2 OH·HCl + Ph 3 P → [(Ph 3 P) 2 N]Cl + 4HCl + Ph 3 PO. A phosphanimine is obtainable from trimethylsilyl azide and triphenylphosphine. Desilylation gives the anion Ph ...
[1] [2] [3] Introduced by Gilbert N. Lewis in his 1916 article The Atom and the Molecule, a Lewis structure can be drawn for any covalently bonded molecule, as well as coordination compounds. [4] Lewis structures extend the concept of the electron dot diagram by adding lines between atoms to represent shared pairs in a chemical bond.
Such a resonance structure is called a Clar structure. In other words, a polycyclic aromatic hydrocarbon with a given number of π-sextets is more stable than its isomers with fewer π-sextets. [1] [2] In 1984, Glidewell and Lloyd provided an extension of Clar's rule to polycyclic aromatic hydrocarbons containing rings of any size. [3]
For example, the pK a value of acetic acid is 4.8, while ethanol has a pK a of 16. Hence acetic acid is a much stronger acid than ethanol. This in turn means that for equimolar solutions of a carboxylic acid or an alcohol in water, the carboxylic acid would have a much lower pH. [1]: 263–7
If R 1 and R 2 (note equation at top of page) are different substituents, there is a new stereocenter formed at the alpha position when an enol converts to its keto form. Depending on the nature of the three R groups, the resulting products in this situation would be diastereomers or enantiomers .