Force distribution analysis of mechanochemically reactive dimethylcyclobutene

Area of Science:

• Computational Chemistry
• Mechanochemistry
• Molecular Dynamics

Background:

• Internal molecular forces are crucial for chemical reactions but difficult to quantify using quantum mechanics.
• Understanding how mechanical forces influence molecular behavior is key to designing new chemical processes.

Purpose of the Study:

• To introduce and validate a novel method, force-matching force distribution analysis (FM-FDA), for analyzing internal molecular forces.
• To investigate the influence of external versus internal mechanical forces on the ring-opening reaction of trans-3,4-dimethylcyclobutene (tDCB).

Main Methods:

• Simulated the ring opening of tDCB using on-the-fly semiempirical molecular dynamics with the self-consistent density functional tight binding (SCC-DFTB) method.
• Applied mechanical force externally (constant pulling) and internally (embedding in a strained macrocycle).
• Analyzed the distribution of internal forces within tDCB using FM-FDA.

Main Results:

• External force application resulted in a symmetric, linearly scaling force distribution in tDCB, dictated by its symmetric structure.
• Internal forces from a strained macrocycle linker induced an asymmetric force distribution, highlighting the linker's role in mechanochemical reactivity.
• Identified key molecular coordinates where force distribution most effectively accelerates the reaction rate.

Conclusions:

• FM-FDA provides a quantitative method to understand and predict mechanochemical reactivity.
• The geometry of force application (external vs. internal linkers) significantly alters internal force distribution and reactivity.
• This approach is valuable for studying complex mechanochemical systems, including those within strained macrocycles.