Two steps in a synthesis of the analgesic ibuprofen include a carbonyl condensation reaction, followed by an alkylation reaction. identify intermediates a and b in the synthesis of ibuprofen.

Ibuprofen is synthesized by reacting ethyl 2-(4-isobutylphenyl)acetate with base, the base abstracts the acidic proton and enolate is formed which on reaction with diethyl carbonate generates diethyl 2-(4-isobutylphenyl)malonate (A). diethyl 2-(4-isobutylphenyl)malonate on treatment with Base again looses the acidic proton and forms enolate. The enolate with treatment with Methyl Iodide yields diethyl 2-(4-isobutylphenyl)-2-methylmalonate (B). diethyl 2-(4-isobutylphenyl)-2-methylmalonate on hydrolysis give Ibuprofen.

They are all full and don't need any more electrons in there outer shell.