AVS 47th International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP32
Hydroxymethylcyclopropane on Oxygen-covered Mo(110): A Radical Clock on a Metal Surface?

Tuesday, October 3, 2000, 5:30 pm, Room Exhibit Hall C & D

Session: Poster Session
Presenter: I. Kretzschmar, Harvard University
Authors: I. Kretzschmar, Harvard University
J.A. Levinson, Harvard University
C.M. Friend, Harvard University
Correspondent: Click to Email
Radical clocks are a well-established means for the determination of radical lifetimes in liquid and gas-phase organic chemistry.@footnote 1@ However, no equivalent tools yet exist for the evaluation of radical lifetimes on surfaces, although radicals are often proposed as the most important intermediates in surface reactions. In this study, the reaction of hydroxymethylcyclopropane has been investigated on clean and oxygen-covered Mo(110) surfaces. Since methylcyclopropane is the expected product upon C-O bond scission in hydroxymethylcyclopropane and represents the smallest possible model system for a radical clock, this molecule seems to be a promising system for gauging radical lifetimes in the vicinity of the surface. Changes in binding and structure of the adsorbate are monitored using a combination of temperature programmed reaction spectrometry and reflectance-infrared absorbance spectroscopy. These studies reveal that the surface species formed upon adsorption of hydroxymethylcyclopropane onto oxygen-covered Mo(110) is stable up to 400 K. Above 450 K, 1-butene, 1,3-butadiene, and ethene are produced. In addition, two new vibrational peaks develop at 1245 cm@super -1@ and 1645 cm@super -1@ in the infrared spectra obtained after heating to 450 K. Both peaks are attributed to ring-opened surface intermediates: the 1645 cm@super -1@ peak to alkoxide species and the 1245 cm@super -1@ peak to the formation of a metal-bound alkyl species after ring opening. The observation of ring-opened products points to the fact that ring opening is faster than hydrogen abstraction from the surface. The experiments are discussed in the general framework of alkyl oxidation processes. @FootnoteText@ @footnote 1@ See for example: Newcomb, M. Tetrahedron, 1993, 49, 1151.