Atomic-Scale Selective C-H Halogenation Driven by Tip Electric Field in Water.

Area of Science:

• Chemistry
• Materials Science
• Physics

Background:

• Precise control over chemical reactions at the atomic level is a key goal.
• C-H bond functionalization is crucial for synthesizing diverse molecules.

Purpose of the Study:

• To achieve precise atomic-level halogenation of C-H bonds.
• To explore the use of nanoconfined electric fields for chemical transformations.

Main Methods:

• Utilizing a scanning tunneling microscope (STM) tip to generate a nanoconfined electric field.
• Employing in situ STM break-junction technique to study reaction kinetics.
• Investigating the effects of electric field strength, halide concentration, and cation type on reaction rates.

Main Results:

• Achieved precise chlorination, bromination, and iodination of α-C-H bonds in carboxylic acids at room temperature in aqueous solutions.
• Reaction kinetics followed pseudo-first-order behavior, influenced by electric field and halide concentration.
• Cesium (Cs+) cations significantly enhanced the reaction rate compared to sodium (Na+) cations.

Conclusions:

• A strong confined electric field induces water dissociation, generating hydroxyl radicals for C-H bond abstraction and subsequent halogenation.
• This work presents a precise, environmentally benign strategy for C-H bond halogenation.
• The method holds potential for green synthesis and atomic-scale manufacturing.