Electrophilicity scales theoretical calculations

This situation is due to the relatively high barrier to rotation of the C-0 bond, making the interconversion between the two isomers (3a and 3b) slow on the NMR time scale. Additional evidence for the 7r-donor effect of alkoxy as well as other groups (mainly alkyl amino) comes from Cr NMR studies and theoretical calculations. Nevertheless, the carbene carbon remains electrophilic, a central feature of Fischer carbenes. 

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