Pseudo-bimolecular [2+2] cycloaddition studied by time-resolved photoelectron spectroscopy.

The first study of pseudo-bimolecular cycloaddition reaction dynamics in the gas phase is presented. We used femtosecond time-resolved photoelectron spectroscopy (TRPES) to study the [2+2] photocycloaddition in the model system pseudo-gem-divinyl[2.2]paracyclophane. From X-ray crystal diffraction measurements we found that the ground-state molecule can exist in two conformers; a reactive one in which the vinyl groups are immediately situated for [2+2] cycloaddition and a nonreactive conformer in which they point in opposite directions. From the measured S(1) lifetimes we assigned a clear relation between the conformation and the excited-state reactivity; the reactive conformer has a lifetime of 13 ps, populating the ground state through a conical intersection leading to [2+2] cycloaddition, whereas the nonreactive conformer has a lifetime of 400 ps. Ab initio calculations were performed to locate the relevant conical intersection (CI) and calculate an excited-state [2+2] cycloaddition reaction path. The interpretation of the results is supported by experimental results on the similar but nonreactive pseudo-para-divinyl[2.2]paracyclophane, which has a lifetime of more than 500 ps in the S(1) state. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Citation

Rasmus Y Brogaard, Andrey E Boguslavskiy, Oliver Schalk, Gary D Enright, Henning Hopf, Vitaly A Raev, Peter G Jones, Ditte L Thomsen, Theis I Sølling, Albert Stolow. Pseudo-bimolecular [2+2] cycloaddition studied by time-resolved photoelectron spectroscopy. Chemistry (Weinheim an der Bergstrasse, Germany). 2011 Mar 28;17(14):3922-31

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PMID: 21365700

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