Photofragment ion imaging with femtosecond real-time clocking has been applied to alpha-bond cleavage from (1)(n, pi*) states of acetylchloride and acetone. It is shown that dissociation occurs within the time comparable with laser pulse duration of 200 fs in acetylchloride, whereas the reaction time is longer than 15 ps in acetone. The dissociation in the neutral state and the fragmentation in the ionic state are discriminated from images of photofragment ion distributions.