The preparation and alkaline hydrolysis of O-18-methyl 2,2-dimethylpro
panoate and O-18-methyl triphenylacetate are reported. From mass spect
ral analysis of the carboxylic acid products, it is concluded that the
former substrate is hydrolyzed exclusively by the B(AC)2 mechanism, w
hereas the latter substrate proceeds 95% by the B(AC)2 mechanism and 5
% by the B(AL)2 mechanism. The balance between these two mechanisms is
discussed.