Silyl anions resonance effects

Another common a-silyl anion is produced by die halogen exchange from a methyl (but not odier group) attached to silicon. Odier a-silyl carbanions can be generated by other processes. Such anions lack the resonance stabilization of an ester group seen in the previous example. They are consequently less stable and must be generated under carefully controlled conditions. They are good nucleophiles and add effectively to aldehydes and ketones. 

The pattern of chemical shift differences found for phenyl-substituted silyl anions is typical for 7i-polarization effects, whereas resonance effects are responsible for electronic effects in carbanions. UV spectroscopic results support this explanation, as carbanions show bathochromic shifts compared to silyl anions [5]. 

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