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The general structure of a hemiacetal (left) and hemiketal (right). 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.
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."
Acetals are stable compared to hemiacetals but their formation is a reversible equilibrium as with esters.As a reaction to create an acetal proceeds, water must be removed from the reaction mixture, for example, with a Dean–Stark apparatus, lest it hydrolyse the product back to the hemiacetal.
In organic chemistry, a functional group is a substituent or moiety in a molecule that causes the molecule's characteristic chemical reactions.The same functional group will undergo the same or similar chemical reactions regardless of the rest of the molecule's composition.
There are five main types of acyl derivatives. Acid halides are the most reactive towards nucleophiles, followed by anhydrides, esters, and amides. Carboxylate ions are essentially unreactive towards nucleophilic substitution, since they possess no leaving group.
With an alcohols or alkoxides to gives the hemiketal or its conjugate base. With a diol to the ketal. This reaction is employed to protect ketones. With sodium amide resulting in C–C bond cleavage with formation of the amide RCONH 2 and the alkane or arene R'H, a reaction called the Haller–Bauer reaction. [21]
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The actual structure shown by spectroscopic studies is the result of rapid hemiketal formation between the 6-OH and the 3-carbonyl groups. Hydration of the 2-carbonyl is also observed. [ 4 ] The lifetime of the stabilized species is commonly said to be about 6 minutes under biological conditions. [ 1 ]