The beta-stabilizing effect of silicon substituent at C-3 on a C-4 cation and a radical in the 2-azetidinone systems is studied using NMR kinetics. While the beta-effect is virtually nonexistent in the case of a cation, a foiled beta-effect (only a 3-fold rate enhancement) is observed for a radical intermediate. From both the experimental and theoretical studies, it is demonstrated that antiaromaticity is playing the prime role in suppressing the beta-stabilizing effect of silicon.