Steric Triplets

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Science  29 Nov 2002:
Vol. 298, Issue 5599, pp. 1681
DOI: 10.1126/science.298.5599.1681c

Time-resolved infrared spectroscopy has provided organic chemists with a wealth of information on short-lived intermediates that appear during chemical reactions. One well-studied system is that of the alkylphenylglycolates, which after absorption of an ultraviolet photon form a triplet state whose evolution to form products such as ketenes can be followed on a time scale of hundreds of nanoseconds.

Merzlikine et al. have now examined these spectral changes at higher resolution and find evidence for the formation of two different np* triplet states that differ in lifetime by about an order of magnitude and arise from the stereochemistry of the alkyl group. Both conformers can decay intermolecularly, but only the shorter-lived Z intermediate decays through an intramolecular pathway (a Norrish Type II elimination) set up by the proximity of the alkyl group to the rest of the molecule. — PDS

J. Am. Chem. Soc. 10.1021/ja282792 (2002).

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