They have the same number of electrons in their outer shells. Elements in the same group often share similar chemical properties because the outer electrons generally determine a lot of their properties
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.