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In organic chemistry, a hemiacetal is a functional group the general formula R 1 R 2 C(OH)OR, where R 1, R 2 is a hydrogen atom or an organic substituent. They generally result from the nucleophilic addition of an alcohol (a compound with at least one hydroxy group ) to an aldehyde ( R−CH=O ) or a ketone ( R 2 C=O ) under acidic conditions.
The term ketal is sometimes used to identify structures associated with ketones (both R groups organic fragments rather than hydrogen) rather than aldehydes and, historically, the term acetal was used specifically for the aldehyde-related cases (having at least one hydrogen in place of an R on the central carbon). [1]
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."
Ethylene glycol protects a ketone (as an acetal) during an ester reduction, vs. unprotected reduction to a diol. A protecting group or protective group is introduced into a molecule by chemical modification of a functional group to obtain chemoselectivity in a subsequent chemical reaction. It plays an important role in multistep organic ...
Hemithioacetal functional group. In organic chemistry, hemithioacetals (or thiohemiacetals) are organosulfur compounds with the general formula R−CH(−OH)−SR’.They are the sulfur analogues of the acetals, R−CH(−OH)−OR’, with an oxygen atom replaced by sulfur (as implied by the thio-prefix).
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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. Selective acetalization of carbohydrate and formation of acetals possessing atypical properties is achieved by using arylsulfonyl acetals.
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