Carbonyl effect

Nickel carbonyl effects coupling of allylic halides when the reaction is carried out in very polar solvents such as DMF or DMSO. This coupling reaction has been used intramolecularly to bring about cyclization of to-allylic halides and was found useful in the preparation of large rings. 

Chrysin shows a similar effect which is much enhanced in tecto-chrysin, owing presumably to methylation of the 7-hydroxyl in techto-chrysin leaving only the keto-associated 5-hydroxyl free in that flavone. Opening the flavone heterocyclic ring to produce 2-hydroxychalcone leaves monophenol activity still partly suppressed because of the remaining carbonyl effect on oxidizability and H-bonding. Since the structure is relatively free to rotate about the ring-to-carbonyl bond, the suppression is less than in tectochrysin. 

A linear solvation energy relationship (LSER) study of tautomerism in aromatic Schiff bases and related azo compounds indicates that the aminoenone tautomer is always the more polar, and is specifically favoured by proton donor solvents (binding to the second lone pair of the carbonyl). Effects of aromatization and benzo fusion are also discussed.26... 

Carbonyl Effect varies according to host molecule glyoxylic acid more adsorbable than acetic but similar in-... 

The symmetric bridging carbonyl, as its name suggests, is equally shared by the two metals to which it is bound. Important examples include weU-known metal carbonyl complexes like Fe2(CO)9 and Co2(CO)g. Although these complexes were partly covered in a previous Structure and Bonding article [8], the theoretical and computational tools available then were too primitive to give proper descriptions of bridging carbonyls effects on these systems. The results from modem theoretical tools are summarized here and in general provide a consensus view of their electronic stmcture. 

Evidently, the C-H bond should hyperconjugate more strongly in acetaldehyde than it does in propene, and the C-H bond length difference as we go from 0° to 90° in torsion angle should increase more. And that s what we find. The calculations show that in this case the C-H bond length increase in acetaldehyde is 0.0047 A, vs. 0.0030 A in propene. This particular type of bond stretching has also been referred to in the literature as the carbonyl effect ... 

Photoexcitation of carbonyls effectively breaks the double bond to form a 1,2-biradical, thus conferring on the more electronegative oxygen atom radical reactivity that closely parallels that of alkoxy radicals. Two multiplicities (singlet and triplet) and two electronic configurations n,n and ji,ji ) have been shown to display reactivity. 

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