We analyze the physical mechanisms underlying control over molecular fragmentation in a family of similar molecules using shaped ultrafast laser pulses. Our interpretation of the control mechanism in one molecule allows us to predict the nature and degree of control possible in the others. The predictions are verified and variations in the control are discussed. This study points to systematic behavior in chemical reactions of similar species driven by photonic reagents. (c) 2005 Elsevier B.V. All rights reserved.