Oxygen atom, interaction with acyl

At the present, the most straightforward mechanism for the formation of J5 from 1 is via insertion of CO into the Th-C(acyl) bond to form a ketene (H, (eq. (4)) which subsequently dimerizes. Presumably, initial CO interaction could involve coordination either to the metal ion as shown or to the electrophilic vacant "carbene p atomic orbital. Considering the affinity of the Th(IV) ion for oxygenated ligands, interaction of the ketene oxygen atom with the metal ion seems reason-... 

Control over the course of the rearrangements of aryl esters can be achieved when the host matrix can interact with the ester and its intermediates through electrostatic or H-bonding interactions. Zeolites and Nafion membranes are two polymeric matrices in which such studies have been conducted. As mentioned above, the positions of the radical centers of the acyl radicals are known to be very near the oxygen atoms of their aryloxy partners at the moment of birth of the radical pairs from the excited singlet state of an aryl ester in all media all subsequent diffusion... 

The rate acceleration and the TT-face selectivity were explained in terms of the coordination of the Lewis acid to the acyl oxygen atom. The binding Lewis acid moiety interacts with the cis- 8-substituent, which forces the olefinic bond to adopt the conformation XXII, approximately orthogonal to the acyl group. The olefinic bond is thus rendered more nucleophilic, accounting for the rapid reaction, and the electrophile E preferentially approaches the face not shielded by the iron auxiliary (Sch. 25). 

The bismuthonium acyl- and sulphonyl-ylides have a completely different appearance and electronic spectra, all of them being yellowish in colour. This is because in their cases, as in those of similar arsonium and stibonium ylides, interaction between an oxygen atom and the bismuth atom is possible, leading to structures such as 48 in accord with this... 

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