Search results
Results from the WOW.Com Content Network
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.
Hemiacetals of ketones (sometimes called hemiketals) are even less stable than those of aldehydes. However, cyclic hemiacetals and hemiacetals bearing electron withdrawing groups are stable. Electron-withdrawing groups attached to the carbonyl atom shift the equilibrium constant toward the hemiacetal.
In contrast to variations of R, both R' groups are organic fragments. If one R' is a hydrogen, the functional group is instead a hemiacetal, while if both are H, the functional group is a ketone hydrate or aldehyde hydrate. Formation of an acetal occurs when the hydroxyl group of a hemiacetal becomes protonated and is lost as water.
The anomeric centre in hemiacetals is the anomeric carbon C-1; in hemiketals, it is the carbon derived from the carbonyl of the ketone (e.g. C-2 in D-fructose). In aldohexoses the anomeric reference atom is the stereocenter that is farthest from the anomeric carbon in the ring (the configurational atom, defining the sugar as D or L ).
A gay Georgia couple convicted of sickening sexually abuse of their two adopted sons will spend the rest of the lives behind bars.. William and Zachary Zulock, 34 and 36, were each sentenced last ...
Main page; Contents; Current events; Random article; About Wikipedia; Contact us
Authorities set on a worldwide chase to find Nicholas Alahverdian, once praised for his work as a child advocate, who has been accused of rape, abuse and fraud.
The average rate on a 30-year mortgage in the U.S. eased for the third week in a row, a welcome trend for prospective homebuyers during what's typically a less competitive time of the year for the ...