Reacting configuration

The expression reacting configuration is often employed in mass spectrometry to signify the particular ion structure which reacts to give certain products [101, 422]. It is an expression whose meaning needs to be examined rather closely, since there is a tendency for it to be used in rather a vague manner. It seems that the expression should mean the ion structure which proceeds directly to the transition state, 

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The decay curves (lifetime distributions) in the microsecond time frame for the formation of (C3HS)+ from the molecular ions of but-l-ene, cis- and frcms-but-2-ene, methylcyclopropane and 2-methylpropene have been determined but the curves could not be described by single rate coefficients. The interpretation put forward was, in effect, that there were two (or more) reacting configurations [20]. Breakdown curves have been reported for butadiyne [210]. 

In contrast to the above results, the acyclic dienes in Egs. (45) [69] and (46) [70] afford only the products of endo carboxylate addition. It is difficult to develop a coherent model to explain these diverse stereochemical results. In addition, it should be noted that rapid geometrical inversion of the N-sulfonyl imines makes the reacting configuration of these species an unknown which complicates analysis [30,31]. 

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