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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 ]
4H-Pyran was first isolated and characterized in 1962 via pyrolysis of 2-acetoxy-3,4-dihydro-2H-pyran. [1] It was found to be unstable, particularly in the presence of air. 4 H -pyran easily disproportionates to the corresponding dihydropyran and the pyrylium ion, which is easily hydrolyzed in aqueous medium.
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.
Some such structures may contain aromatic π-sextets, namely groups of six π-electrons localized in a benzene-like moiety and separated by adjacent rings through C–C bonds. An aromatic π-sextet can be represented by a circle, as in the case of the anthracene molecule (below). Clar's rule states that for a benzenoid polycyclic aromatic ...
Thiopyran is a heterocyclic compound with the chemical formula C 5 H 6 S. [1] It has two isomers, 2H-thiopyran and 4H-thiopyran, which differ by the location of double bonds. Thiopyrans are analogous to pyrans in which the oxygen atoms have been replaced by sulfur atoms.
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 ...
Scheme 4 depicts this 4 component reaction with the ethyl ester of glyoxylic acid, 3,4-dihydro-2H-pyran, aniline and ethanol with lewis acid scandium(III) triflate and molecular sieves. Scheme 4 Four component Povarov reaction. In order to clarify the role of the lewis acid, a solid scandium nitrogen bond is drawn.
In IUPAC names, "dihydro" refers to the two added hydrogen atoms needed to remove one double bond from the parent compound pyran. The numbers in front of the prefix indicate the position of the added hydrogen atoms (and not the position of the double bonds). [ 1 ]