Femtosecond observation of benzyne intermediates in a molecular beam: Bergman rearrangement in the isolated molecule
In this communication, we report our femtosecond real-time observation of the dynamics for the three didehydrobenzene molecules (p-, m-, and o-benzyne) generated from 1,4-, 1,3-, and 1,2-dibromobenzene, respectively, in a molecular beam, by using femtosecond time-resolved mass spectrometry. The time required for the first and the second C-Br bond breakage is less than 100 fs; the benzyne molecules are produced within 100 fs and then decay with a lifetime of 400 ps or more. Density functional theory and high-level ab initio calculations are also reported herein to elucidate the energetics along the reaction path. We discuss the dynamics and possible reaction mechanisms for the disappearance of benzyne intermediates. Our effort focuses on the isolated molecule dynamics of the three isomers on the femtosecond time scale.
Additional Information© 2000, The National Academy of Sciences. Contributed by Ahmed H. Zewail, December 2, 1999. We thank Mr. Hans-Christian Becker for his helpful assistance and discussion. This work was supported by the U.S. Air Force Office of Scientific Research and the Office of Naval Research. Acknowledgement is also made to the donors of the Petroleum Research Fund administered by the American Chemical Society for support of this research. The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. Article published online before print: Proc. Natl. Acad. Sci. USA, 10.1073/pnas.030524797. Article and publication date are at www.pnas.org/cgi/doi/10.1073/pnas.030524797
Published - DIApnas00.pdf