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Keto–enol tautomerism refers to a chemical equilibrium between a "keto" form (a carbonyl, named for the common ketone case) and an enol. The interconversion of the two forms involves the transfer of an alpha hydrogen atom and the reorganisation of bonding electrons. The keto and enol forms are tautomers of each other. [2]
Molecular orbitals of an enolate, showing the occupancy corresponding to the anion. Enolate anions are electronically related to allyl anions. The anionic charge is delocalized over the oxygen and the two carbon sites. Thus they have the character of both an alkoxide and a carbanion. [5]
Enolase is a member of the large enolase superfamily.It has a molecular weight of 82,000–100,000 daltons depending on the isoform. [3] [4] In human alpha enolase, the two subunits are antiparallel in orientation so that Glu 20 of one subunit forms an ionic bond with Arg 414 of the other subunit. [3]
As a result, enolate ions are more common than enols in both laboratory and biological chemistry. Because they are resonance hybrids of two nonequivalent forms, enolate ions can be looked at either as vinylic alkoxides (C=C- O −) or as α-ketocarbanions (− C-C= O). Thus, enolate ions can react with electrophiles either on oxygen or on carbon.
The mechanism of the enzyme requires removal of the α-proton of the 2-methylacyl-CoA to form a deprotonated intermediate (which is probably the enol or enolate [10]) followed by non-sterespecific reprotonation. [11] Thus either epimer is converted into a near 1:1 mixture of both isomers upon full conversion of the substrate.
KSI catalyzes the rearrangement of a carbon-carbon double bond in ketosteroids through an enolate intermediate at a diffusion-limited rate. [2] There have been conflicting results on the ionization state of the intermediate, whether it exists as the enolate [12] or enol. [13]
The general structure of a silyl enol ether. In organosilicon chemistry, silyl enol ethers are a class of organic compounds that share the common functional group R 3 Si−O−CR=CR 2, composed of an enolate (R 3 C−O−R) bonded to a silane (SiR 4) through its oxygen end and an ethene group (R 2 C=CR 2) as its carbon end.
Malondialdehyde results from lipid peroxidation of polyunsaturated fatty acids. [3] It is a prominent product in thromboxane A2 synthesis wherein cyclooxygenase 1 or cycloxygenase 2 metabolizes arachidonic acid to prostaglandin H2 by platelets and a wide array of other cell types and tissues.