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4-Pyrone (γ-pyrone or pyran-4-one) is an unsaturated cyclic chemical compound with the molecular formula C 5 H 4 O 2.It is isomeric with 2-pyrone. Preparation [ edit ]
In 2H-pyran, the saturated carbon is at position 2, whereas, in 4H-pyran, the saturated carbon is at position 4. It must be noted that “oxine” must not be used for pyran because it has been used as a trivial name for quinolin-8-ol. [1] 4H-Pyran was first isolated and characterized in 1962 via pyrolysis of 2-acetoxy-3,4-dihydro-2H-pyran. [2]
An aromatic ring can assist in the formation of a carbocationic intermediate called a phenonium ion by delocalising the positive charge. When the following tosylate reacts with acetic acid in solvolysis then rather than a simple S N 2 reaction forming B, a 48:48:4 mixture of A, B (which are enantiomers) and C+D was obtained. [7] [8]
Tetrahydropyran (THP) is the organic compound consisting of a saturated six-membered ring containing five carbon atoms and one oxygen atom. It is named by reference to pyran, which contains two double bonds, and may be produced from it by adding four hydrogens.
The pyranose ring is formed by the reaction of the hydroxyl group on carbon 5 (C-5) of a sugar with the aldehyde at carbon 1. This forms an intramolecular hemiacetal.If reaction is between the C-4 hydroxyl and the aldehyde, a furanose is formed instead. [1]
Homoaromaticity, in organic chemistry, refers to a special case of aromaticity in which conjugation is interrupted by a single sp 3 hybridized carbon atom. Although this sp 3 center disrupts the continuous overlap of p-orbitals, traditionally thought to be a requirement for aromaticity, considerable thermodynamic stability and many of the spectroscopic, magnetic, and chemical properties ...
The nitrogen (N)-containing aromatic rings can be separated into basic aromatic rings that are easily protonated, and form aromatic cations and salts (e.g., pyridinium), and non-basic aromatic rings. In the basic aromatic rings , the lone pair of electrons is not part of the aromatic system and extends in the plane of the ring.
Hückel's rule is not valid for many compounds containing more than one ring. For example, pyrene and trans-bicalicene contain 16 conjugated electrons (8 bonds), and coronene contains 24 conjugated electrons (12 bonds). Both of these polycyclic molecules are aromatic, even though they fail the 4n + 2 rule. Indeed, Hückel's rule can only be ...