Carboxylic esters, exchange labeling

Poly(vinyl acetate), PVAc, of molecular weights (M ) 6.1x1 01, 1.9xl05, and 6.0xl05, was randomly labeled by ester exchange with 2,2,5,5-tetramethyl-3-pyrrolin-l-oxyl-3-carboxylic acid to give a spin labeled polymer containing typically 1-10 nitroxides per polymer molecule. Polystyrene was prepared by emulsion... 

The mechanism of CO substitution with phosphines in the 19-e complex Cp Mn(CO)2NO is dissociative, followed by spontaneous oxidation of the product. Trinuclear clusters containing CpRe(CO)-fiagments in combination with iron carbonyl sulfido dimers have been reported. The synthesis of CpMn(CO)2(n -cyclooctyne) and the ligand rearrangement to an allene complex within the metal coordination sphere has been investigated by NMR spectroscopy. Tc labelled esters of cytectrene carboxylic acid have been prepared by exchange with ferrocenylcarboxylic acids in the presence of carbonyl donors. ... 

Probably the most widely cited evidence for the existence of a tetrahedral intermediate comes from isotopic exchange reactions. For example, in the reaction of a carboxylic acid derivative, such as an ester, the two OH groups in the tetrahedral intermediate are equivalent (examine the T.L in Scheme 10.22). If the reaction were performed in 0-labeled water, one of these OH groups would be isotopically labeled. Reversal of the nucleophilic addition step would exchange the 0 into the carbonyl oxygen 50% of the time. As the reaction proceeds... 

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