Question

(a) Give the Claisen ester condensation product of ethyl butanoate.
(b) Why does the Claisen ester condensation of ethyl-2-methyl propanoate `(I)` not take place ?
( c) Why does Claisen condensation of `(I)` take place by the use of `Ph_3 C^(Ө) Na^(oplus)` as a base ?

Answer 1

(a)
Although this reaction is reversible, it proceeds to completion by the formation of a very stable carbonion

(b)
the product `(II)` is without an acidic `H` between the two `(C=O)` groups. The reaction reverts to the more stable reactant ester rather proceedings towards completion.
( c) `Ph_3 C^(Ӫ)` is a very strong base and is capable of removing less acidic `H` atom (at `C-4)`, that is, `alpha`-to the keto `(C=O)` forming , and favours the reaction for completion.