Unknown Regiochemistry

The zirconium complex 315 reacts with diphenylacetylene to give the coupling product 326 [Eq. (55)].116 The regiochemistry of the reaction parallels that of an acyclic allene complex.133 Complex 315 also reacts with stilbene, but in this case, the seven-membered ring is displaced from the metal. The fate of the seven-membered ring is unknown. 

Mass spectrometry (MS) is faster than NMR and has much better sensitivity the result (e.g. a molecular weight) can also be easier to interpret automatically -so MS may be the method of choice for structure confirmation, particularly in surveying large numbers of samples such as those that result from combinatorial or array chemistry. However, MS rarely gives sufficient information to elucidate fully the stmctures of unknowns and NMR is required, especially to settle questions of regiochemistry. 

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