Through Stronger Hinderance to Higher Reactivity: Real-time XPS-measurements on the Activation Energy of Ether Cleavage on Silicon
Reactivity in surface chemistry is often discussed in terms of the interaction between surface states and the functional groups of the reacting molecule. Comparing diethyl ether and butyl methyl ether, which exhibit the same functional group but differ in the length of the alkyl chains, we could demonstrate that these seemingly innocent side chains can also play a decisive role. By means of real-time XPS-measurements at the synchrotron SOLEIL, of which the experimental hall at sun set is depicted in the background of our picture, we could directly compare the activation energies for ether cleavage for the two molecules on Si(001). In contrast to a simple expectation, the in general stronger steric hindrance of butyl methyl ether leads to a lower activation energy for ether cleavage on Si(001) when compared to diethyl ether. DFT calculations reproduced the experimental findings when taking into account a finite submonolayer surface coverage leading to different degrees of destabilization of the precursor and the transition state depending on the length of the alkyl chains involved (compare schematic energy curve and ball-and-stick models at different coverage). Given the fact that for almost all technologically relevant processes surface coverage is typically above the isolated-molecule limit, these findings are of general importance for surface functionalization and can help to properly design future experiments.
Publication: T. Glaser, G. F. Nolte, T. Bohamud, P. Keller, M. G. Silly, H. Weiske, R. Tonner-Zech, M. Dürr, Through Stronger Hinderance to Higher Reactivity: Influence of the Alkyl Chains on the Activation Energy of Ether Cleavage on Silicon, Angew. Chem. Int. Ed. 65, e19990 (2026). DOI: 10.1002/anie.202519990
