Abstract
Any long-lived chemical structure in solution is subject to statistical energy equilibration, so the history of any specific structure does not affect its subsequent reactions. This is not true for very short-lived intermediates because energy equilibration takes time. Here, this idea is applied to achieve the ‘energy labelling’ of a reactive intermediate. The selectivity of the ring-opening α-cleavage reaction of the 1-methylcyclobutoxy radical is found here to vary broadly depending on how the radical was formed. Reactions that provide little excess energy to the intermediate lead to a high selectivity in the subsequent cleavage (measured as a kinetic isotope effect), whereas reactions that provide more excess energy to the intermediate exhibit a lower selectivity. Accounting for the expected excess energy allows the prediction of the observed product ratios and, in turn, the product ratios can be used to determine the energy present in an intermediate.
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Acknowledgements
We thank the National Institutes of Health (grant GM-45617) for financial support. H.K. thanks the Japan Society for the Promotion of Science for a Postdoctoral Fellowship for Research Abroad. We thank J. Martin for a preliminary study of the synthesis and reaction of 9.
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H.K. carried out all the experimental work and most of the computations, and chose the specific systems studied. Both authors analysed the results. D.A.S. conceived the general idea and wrote most of the manuscript.
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Kurouchi, H., Singleton, D. Labelling and determination of the energy in reactive intermediates in solution enabled by energy-dependent reaction selectivity. Nature Chem 10, 237–241 (2018). https://doi.org/10.1038/nchem.2907
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DOI: https://doi.org/10.1038/nchem.2907
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