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Ketones are trigonal planar around the ketonic carbon, with C–C–O and C–C–C bond angles of approximately 120°. Ketones differ from aldehydes in that the carbonyl group (C=O) is bonded to two carbons within a carbon skeleton. In aldehydes, the carbonyl is bonded to one carbon and one hydrogen and are located at the ends of carbon chains.
However, this problem can be avoided if one of the compounds does not contain an α-hydrogen, rendering it non-enolizable. In an aldol condensation between an aldehyde and a ketone, the ketone acts as the nucleophile, as its carbonyl carbon does not possess high electrophilic character due to the +I effect and steric hindrance. Usually, the ...
Geminal diols can be viewed as ketone (or aldehyde) hydrates. The two hydroxyl groups in a geminal diol are easily converted to a carbonyl or keto group C=O by loss of one water molecule. Conversely, a keto group can combine with water to form the geminal hydroxyl groups. The equilibrium in water solution may be shifted towards either compound.
Aldehyde structure. In organic chemistry, an aldehyde (/ ˈ æ l d ɪ h aɪ d /) is an organic compound containing a functional group with the structure R−CH=O. [1] The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl group. Aldehydes are a common motif in many ...
In an aldol condensation, water is subsequently eliminated and an α,β-unsaturated carbonyl is formed. The aldol cleavage or Retro-aldol reaction is the reverse reaction into the starting compounds. The name aldehyde-alcohol reaction derives from the reaction product in the case of a reaction among aldehydes, a β-hydroxy aldehyde.
A Knoevenagel condensation is a nucleophilic addition of an active hydrogen compound to a carbonyl group followed by a dehydration reaction in which a molecule of water is eliminated (hence condensation). The product is often an α,β-unsaturated ketone (a conjugated enone). General Knoevenagel layout
Aldehydes and to some extent even ketones, hydrate to geminal diols. The reaction is especially dominant for formaldehyde, which, in the presence of water, exists significantly as dihydroxymethane. Conceptually similar reactions include hydroamination and hydroalkoxylation, which involve adding amines and alcohols to alkenes.
The use of aldehyde in the name comes from its history: aldehydes are more reactive than ketones, so that the reaction was discovered first with them. [2] [3] [4] The aldol reaction is paradigmatic in organic chemistry and one of the most common means of forming carbon–carbon bonds in organic chemistry.