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Generic structure of acetals. In organic chemistry, an acetal is a functional group with the connectivity R 2 C(OR') 2.Here, the R groups can be organic fragments (a carbon atom, with arbitrary other atoms attached to that) or hydrogen, while the R' groups must be organic fragments not hydrogen.
In IUPAC nomenclature, an acetyl group is called an ethanoyl group. An acetyl group contains a methyl group (−CH 3) that is single-bonded to a carbonyl (C=O), making it an acyl group. The carbonyl center of an acyl radical has one non-bonded electron with which it forms a chemical bond to the remainder (denoted with the letter R) of the molecule.
Acid catalyzed acetal formation from the corresponding hemiacetal. Acetals, as already pointed out, are stable tetrahedral intermediates so they can be used as protective groups in organic synthesis. Acetals are stable under basic conditions, so they can be used to protect ketones from a base. The acetal group is hydrolyzed under acidic conditions.
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In organic chemistry, a ketal is a functional group derived from a ketone by replacement of the carbonyl (C=O) group by two alkoxy groups. The IUPAC once declared the term "ketal" obsolete, but later accepted it as a subclass of acetals. Therefore, a ketal can also be defined as "an acetal derived from a ketone."
The acetyl group (indicated in blue in the structural diagram on the right) of acetyl-CoA is linked to the sulfhydryl substituent of the β-mercaptoethylamine group. This thioester linkage is a "high energy" bond, which is particularly reactive.
The intermediate collapses and expels the leaving group (X) to give the substitution product 3. While nucleophilic acyl substitution reactions can be base-catalyzed, the reaction will not occur if the leaving group is a stronger base than the nucleophile (i.e. the leaving group must have a higher pK a than the nucleophile). Unlike acid ...
The latter reagent in itself is an acetal and therefore the reaction is actually a cross-acetalisation. Kinetic reaction control results from 2-methoxypropene as the reagent. D-ribose in itself is a hemiacetal and in equilibrium with the pyranose 3. In aqueous solution ribose is 75% pyranose and 25% furanose and a different acetal 4 is formed.