Chemical Bonding in Three-Membered Ring Systems

Area of Science:

• Computational chemistry
• Theoretical inorganic chemistry

Background:

• Investigating the formation and decomposition of cyclic silicon-carbon compounds is crucial for understanding their reactivity.
• Previous studies have explored similar reactions, but the detailed mechanistic pathways, especially concerning symmetry and diabatic processes, require further elucidation.

Purpose of the Study:

• To computationally investigate the reaction mechanisms for forming and eliminating three-membered rings involving silicon and carbon.
• To analyze charge and spin redistribution during these reactions using advanced quantum chemical methods.
• To understand the role of symmetry (C2v and Cs) in determining reaction pathways and energy profiles.

Main Methods:

• Utilized CAS(4,4) wave functions for electronic structure calculations.
• Employed the orthogonal valence bond (OVB) method to analyze charge and spin redistribution.
• Examined potential energy curves and internal coordinates for various reaction pathways.

Main Results:

• Addition and elimination reactions frequently follow different minimum energy paths, indicating diabatic behavior.
• Diabatic reactions in C2v symmetry lack energy barriers, characterized by energy increases followed by a "jump" to another state.
• In Cs symmetry, diabatic states combine into an adiabatic pathway, resulting in a single minimum energy path.

Conclusions:

• The study reveals that symmetry plays a critical role in the nature of reaction pathways for these silicon-carbon ring systems.
• Diabatic reactions are common, with distinct pathways for addition and elimination, especially in higher symmetry.
• The transition to lower symmetry allows for the coupling of diabatic states into a single adiabatic reaction path.