Investigating Solvent-free Reactions: An energy-based Evalution of Reaction Pathways Introduction By researching various reactions under solvent-free conditions, we can identify the optimal products may form. Several possible transformations of a fluorinated aromatic compound were analyzed. By comparing the energies of the reactants, the charged intermediate, and the radical structure, we can determine which reaction pathways are most energetically favorable. We are also able to determine whether the products formed are stable relative to the reactants used.
Computational Details Geometry optimizations were run with the PBE density functional and a TZVP basis set in Gaussian.
Reactants forming the carbocation
Figure 2. charged intermediate reactant.
Figure 1. Products of the ether-formation pathway: C₁₉H₁₅F and CH₃OH.
Results The calculated energies (ΔE) demonstrated clear differences in favoribility among the solvent-free reactions investigated. Formation of the ether products (figure 1.) was the most favorable reaction with a calculated energy of -0.246 Hartree. The Friedel-Crafts pathway (figure 3.) was mildly favorable, showing and energy of -.0148 Hartree. The charged intermediate reaction (figure 2.) showed the highest energy result of +0.28 Hartree, making it the least favorable reaction demonstrated. The products of the hydrogen-replacement pathway (figure 4.) were close to a neutral energy, measured at +0.0155 Hartree. Overall, the data demonstrates that solvent-free reactions strongly favor ether formation over fluorine substitution pathways.
Delta(E) [eV]
Reactant to Intermediates 7.631 with Charge Reactant to Ether
-6.702
Reactant to Friedel-Crafts Product
-0.402
Reactant to H-Replacement
0.421
Figure 3. reactant of the Friedel-Crafts pathway.
Figure 4. reactant of the hydrogen-replacement reaction
Conclusion Among the solvent-free mechanisms examined, the results demonstrate that products of an ether-formation pathway (Figure 1.) are energetically the most favorable. Compared to the carbocation, Friedel-Crafts, and hydrogen replacement pathways, ether formation indicated a strong driving force for methanol substitution. These findings suggest that without a solvent, the reaction is more likely to form the ether rather than keeping the fluorine or making less stable intermediates. Overall, the energy results show that ether formation is the most favorable pathway.