Stability of carbonyl group

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 m an alkene is more stable than a monosubstituted double bond a ketone carbonyl is more stable than an aldehyde carbonyl We 11 see later m this chapter that structural effects on the relative stability of carbonyl groups m aldehydes and ketones are an important factor m then rel ative reactivity... 

Increasing stabilization of carbonyl group decreasing K for hydration... 

Resonance stabilization of carbonyl group by methoxy group disfavors the addition reaction. 

Alkyl substituents stabilize a carbonyl group m much the same way that they sta bilize carbon-carbon double bonds and carbocations—by releasing electrons to sp hybridized carbon Thus as then heats of combustion reveal the ketone 2 butanone is more stable than its aldehyde isomer butanal... 

Instead of stabilizing the carbonyl group by electron donation as alkyl substituents do trifluoromethyl groups destabilize it by withdrawing electrons A less stabilized carbonyl group IS associated with a greater equilibrium constant for addition... 

What structural features are responsible for the reactivity order of carboxylic acid derivatives Like the other carbonyl containing compounds that we ve studied they all have a planar arrangement of bonds to the carbonyl group Thus all are about the same in offering relatively unhindered access to the approach of a nucleophile They differ m the degree to which the atom attached to the carbonyl group can stabilize the carbonyl group by electron donation... 

Electron release from the substituent X not only stabilizes the carbonyl group it decreases the positive character of the carbonyl carbon and makes the carbonyl group less electrophilic... 

Electron release from nitrogen stabilizes the carbonyl group of amides and decreases the rate at which nucleophiles attack the carbonyl carbon... 

An extreme example of carbonyl group stabilization is seen m carboxylate anions... 

Most methods for their preparation convert one class of carboxylic acid derivative to another and the order of carbonyl group stabilization given m Figure 20 1 bears directly on the means by which these transformations may be achieved A reaction that converts one carboxylic acid derivative to another that lies below it m the figure is pracfical a reacfion fhaf converts if fo one fhaf lies above if is nol This is anofher way of saying fhaf one carboxylic acid derivative can be converted to another if the reaction leads to a more stabilized carbonyl group Numerous examples of reacfions of fhis fype will be pre senfed m fhe secfions fhaf follow... 

Section 20 13 Thioesters undergo reactions analogous to those of esters but at faster rates A sulfur atom stabilizes a carbonyl group less effectively than an oxygen... 

Table 8.6. Relative Stabilization of Carbonyl Compounds by Substituent Groups"...

However, treatment of 4-chloro-3-nitrocoumarin (81) with 2-mercaptophenol (254) provided the product of displacement of the chlorine atom 263. Treatment of compound 263 with triethylamine gave a mixture from which low yields of 266 and 267 were isolated (92ZOR1489). This fact can be explained by the formation of the o-complex 264. This complex is stabilized by carbonyl group participation and therefore an equilibrium of 263 and 265 can be expected. This is in accordance with the formed products (Scheme 41). A similar situation was described earlier for the reaction of 4,5-dichloropyridazin-6(17/)-one with the disodium salt of 2-mercaptophenol (82JHC1447). 

The stability of carbonyls of a metal in the +3 oxidation state is unusual because d7r-p7r back donation is necessary to stabilize the Ir-C bond, generally only one CO group can be bonded to the electron-deficient Ir3+. 

The regioselective ring opening of the silyl epoxides is facilitated by the stabilizing effect that silicon has on a positive charge in the -position. This facile transformation permits vinylsilanes to serve as the equivalent of carbonyl groups in multistep synthesis.149... 

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