Femtosecond dynamics of diradicals: transition states, entropic configurations and stereochemistry

With femtosecond-resolved mass spectrometry, we report real-time studies of the dynamics of reactive diradicals: trimethylene, tetramethylene and stru cturally-constrained (by a bridge) tetramethylene. These comparative studie s elucidate the role of transition states, entropic configurations and IVR on the global potential energy surface. The critical time scale for rotatio nal clocks in stereochemistry is illustrated in the reaction mechanism for cyclization and fragmentation products. (C) 1999 Elsevier Science B.V. All rights reserved.