Ester carbonyl group

Most stable enol double bond conjugated with carbonyl group ester carbonyl stabilized by resonance... 

The discussion above emphasizes that the allyl-Ni reagents are quite selective for carbon halogen bonds, especially allyl, vinyl, and aryl halides. At the same time, modest reactivity as nucleophiles toward reactive carbonyl derivatives has been reported.Simple aldehydes, the more reactive ketones (such as cyclopentanone and benzoquinone), and certain epoxides will undergo 1,2-addition of the aUyl ligand to the carbonyl group. Esters, amides, and, most remarkably, acyl halides are inert toward the allyl Ni reagents under conditions where the reagents do not decompose thermally (<80 °C or so). 

The reaction exhibits extraordinary chemoselectivity and an isolated carbonyl group, ester, unprotected alcohol, alkyne and terminal alkene are unaffected by this catalytic system. Notably, the geometry of the resulting alkene moiety is controlled to be E (Eq. 12.10). 

These reagents are interesting because aldehydes and ketones are affected in acidic media only, which permits the reduction of carbon-halogen bonds (Section 2.1) without affecting carbonyl groups, esters, or nitriles. 

Aspirin is a phenyl ester. Phenyl esters arc considerably more susceptible to hydrolysis than ordinary esters are, for two reasons Delocalization of a lone electron pair from the phenol oxygen into the carbonyl group (ester rc.sonance. 

Aspirin is a phenyl ester. Phenyl esters arc considerably more susceptible to hydrolysis than ordinary esters arc. for two reasons Delocalization of a lone electron pair from the phenol oxygen into the carbonyl group (ester resonance, sec Section 20-1) is diminished, because this lone pair is also in resonance with the benzene ring. The result is a greater 8 on the carbonyl carbon, which facilitates nucleophilic attack. The... 

Similar to other molecules presenting a carbonyl group, esters are polar molecules (e.g., ketones and aldehydes) and therefore create dipole—dipole interactions as well as van der Waals dispersion forces. 

By IR-spectroscopy a decrease was observed in the keto-carbonyl groups (ester groups at 1740 cm aldehyde groups at 1720 cm and ketone groups at 1715 cm ) during microbial assimilation (i.e. biotic step) as a result of release of short-chain carboxylic as degradation products [5-8]. 

After Zn(OAc)2 transmetalation Pd-catalyzed cross-coupling with the bromothiophene 18 provides the substituted thiophene 19 in 75% yield. The presence of carbonyl groups (ester or amide) precludes the use of TiCLr, Bids, or InCls as additives. However, by employing 3% PbCl2 a smooth insertion reaction with several functionalized iodides, such as 20 and 21, or with the bromide 22 (Scheme 1) [10] occurs, providing the derived functionalized aluminum reagents 23-25 in good yields. 

The reverse reaction of esterification is hydrolysis. Both esterification and ester hydrolysis are add-catalyzed. The mechanism involves protonation of the oxygen of the carbonyl group, allowing nucleophiUc attack by water or alcohol at the carbon atom of the carbonyl group. Ester formation cannot be base-catalyzed but the hydrolysis can be catalyzed by OH ions, which attack the carbon atom of the carbonyl group. This type of hydrolysis is known as saponification (because it is the reaction used to make soap from fats and oils). 

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