Carbonyl group in aldehydes and ketones

The carbonyl carbon of a ketone bears two electron-releasing alkyl groups an aldehyde carbonyl group has only one. Just as a disubstituted double bond in an alkene is more stable than a monosubstituted double bond, a ketone carbonyl is more stable than an aldehyde carbonyl. We ll see later in this chapter that structural effects on the relative stability of carbonyl groups in aldehydes and ketones are an important factor in their relative reactivity. 

Methods for the protection of the carbonyl group in aldehydes and ketones are considered in Section 5.8.8. 

It is, of course, not correct to treat the wave function of a polyatomic molecule as localized in the chromophoric group considered responsible for the optical absorption. The carbonyl group in aldehydes and ketones gives rise to absorption which extends from about 3430 A to about 2200 A (as well as to absorption at shorter wavelengths). Nevertheless the carbon-oxygen bond is never broken by absorption at these wavelengths. Frequently an adjacent bond is broken but often more complex processes occur. It is sometimes possible to describe these processes in terms of quantum mechanics but some of them should not be treated as direct dissociations. 

Both LLAIH4 and NaBH4 reduce polar carbonyl groups in aldehydes and ketones, but normally do not reduce simple alkenes or alkynes. 

Hydrocyanation is the formal addition of hydrogen cyanide to alkenes. alkynes, and dienes to yield nitriles. These reactions can be catalyzed by various copper, cobalt, nickel and palladium catalysts modified with phosphanes and phosphites and/or Lewis acids. Hydrocyanation of carbonyl groups in aldehydes and ketones is covered in Section D.l.3.7. 

The carbonyl group in aldehydes and ketones will react with hydrazine derivatives. Hydrazine is related to ammonia ... 

Carbonyl groups in aldehydes and ketones add to 1,3-dienes and the reaction has been used to prepare derivatives of 5,6-dihydropyrans. Formaldehyde reacts only slowly but reactivity increases with reactive carbonyl compounds bearing electron-withdrawing groups, such as glyoxylate derivatives (3.22). 

Acetylides are strong bases and are good nucleophiles. So they can add to the carbonyl groups in aldehydes and ketones. The alkoxide ion that is formed during the reaction can be protonated to an alcohol by treating it with aqueous dilute acid. 

Aldehydes and ketones are compounds containing the acyl group. The carbonyl group present in them is polar because of the electronegativity of oxygen. It is noteworthy to mention that the carbonyl group in aldehydes and ketones are very reactive. 

This reaction was first reported by Clemmensen of Park Davis Co in 1913. It is the reduction of carbonyl groups (in aldehydes and ketones) to methylene groups with zinc amalgam and hydrochloric acid, and is generally known as the Clemmensen reduction. In... 

The most common reaction theme of acid halides, anhydrides, esters, and amides is the addition of a nucleophile to the carbonyl carbon to form a tetrahedral carbonyl addition intermediate. To this extent, the reactions of these functional groups are similar to nucleophilic addition to the carbonyl groups in aldehydes and ketones (Section 12.4). The tetrahedral carbonyl addition intermediate (TCAI) formed from an aldehyde or a ketone then adds H". The result of this reaction is nucleophilic addition to a carbonyl group of an aldehyde or a ketone ... 

How does the carbonyl group s structure (Section 17-2) help us understand the way it functions chemically We shall see that the carbon-oxygen double bond is prone to additions, just like the ir bond in alkenes. Being highly polar, however, it is predisposed toward attack by nucleophiles at carbon and electrophiles at oxygen. This section begins the discussion of the chenustry of the carbonyl group in aldehydes and ketones. 

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