# Through Stronger Hindrance to Higher Reactivity: Influence of the Alkyl Chains on the Activation Energy of Ether Cleavage on Silicon

## TL;DR

This paper shows that side chains on molecules can significantly affect chemical reactions on silicon surfaces, sometimes in unexpected ways.

## Contribution

The study reveals that stronger steric hindrance can lead to lower activation energy for ether cleavage on silicon surfaces.

## Key findings

- Butyl methyl ether has lower activation energy for ether cleavage on Si(001) than diethyl ether.
- Steric hindrance from side chains affects precursor and transition state destabilization differently.
- Findings are relevant for surface functionalization and experimental design at submonolayer coverage.

## Abstract

Reactivity in surface chemistry is often discussed in terms of the interaction between surface states and the functional groups of the reacting molecule. Herein, we demonstrate that for finite submonolayer coverage, i.e., surface coverage at which the molecular adsorbates cannot be treated as isolated molecules anymore, the seemingly innocent side chains of the adsorbate can also play a decisive role. For the example of ether cleavage on Si(001), which represents the surface analogue of an SN2‐type reaction, we show both experimentally and based on ab initio calculations that steric hindrance by the side chains determines the activation energy for C‐O dissociation into the final state. In contrast to a simple expectation, the stronger steric hindrance of the butyl group in butyl methyl ether leads to a lower activation energy for ether cleavage on Si(001) when compared to diethyl ether. This effect was traced back to different degrees of destabilization of the precursor and the transition state. Given the fact that for almost all technologically relevant processes the surface coverage is typically above the isolated‐molecule limit, our findings are of general importance for surface functionalization and can help to properly design future experiments.

For ether cleavage on Si(001), steric hindrance by the side chains was shown to determine the reactivity on the surface. In contrast to a simple expectation, the stronger steric hindrance of the butyl group in butyl methyl ether leads to a lower activation energy for ether cleavage on Si(001) when compared to diethyl ether. This effect was traced back to different degrees of destabilization of the precursor and the transition state.