Alkynes substituent parameters

Thus, 5-hexynyllithiums bearing an alkyl, aryl, or trimethylsilyl substituent on the terminal alkyne carbon cyclize readily upon warming to room temperature and the exocyclic vinylic organolithium 14 derivative may be trapped by reaction with different electrophiles. The alkyl-substituted system such as dec-5-ynyllithium 13a (R = Bu) undergoes clearly first-order cyclization to l-(cyclopentylidene)pentyllithium 14a (R = Bu) with a half-life of 7 min at 28.8 °C, and the activation parameters that characterize this reaction indicate that the rate of cyclization is strongly dependent on the temperature. 

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