Reaction activity and selectivity are top priorities in chemistry. Two strategies are usually adopted to increase the activity: either raising the reaction temperature or lowering the reaction energy barrier. However, the reaction selectivity may be complicated by diverse byproducts. Peilin Liao, Purdue University, West Lafayette, IN, USA, Xiang Shao, University of Science and Technology of China, Hefei, Kurt V. Gothelf, Aarhus University, Denmark, Kai Wu, Peking University, Beijing, China, and colleagues have used a self-assembly strategy to control the regioselectivities of the reactions of fluorinated molecules on gold surfaces.

In the Arrhenius equation, the reaction rate constant is expressed as k = A·e^-Ea/RT. The pre-exponential factor A relates to the ordering, environment, and nature of the reacting molecules. The scientists used their assembly strategy to tune the molecular packing patterns and the reaction regioselectivity by confining the molecule docking sites. This increases the pre-exponential factor and, thus, enhances the rate constant.

This strategy turned out to be very efficient in suppressing side reactions and increasing reaction selectivity by greatly narrowing down the product distribution. This study brings a new application of surface reaction control to the molecular assembly approach.

• Steering On-Surface Reactions by a Self-Assembly Approach,
  Qiwei Chen, Jacob R. Cramer, Jing Liu, Xin Jin, Peilin Liao, Xiang Shao, Kurt V. Gothelf, Kai Wu,
  Angew. Chem. Int. Ed. 2017, 56, 5026–5030.
  DOI: 10.1002/anie.201700745