Insights into the Reactivity of the Ring-Opening Reaction of Tetrahydrofuran by Intramolecular Group-13/P- and Al/Group-15-Based Frustrated Lewis Pairs

Deciphering the conformational preference and ionization dynamics of tetrahydrofuran: Insights from advanced spectroscopic techniques

Tetrahydrofuran (THF) has garnered significant attention due to its pivotal role in biological and chemical processes. The diverse array of conformations exhibited by THF profoundly impacts its reactivity and interactions with other molecules. Understanding these conformational preferences is crucial for comprehending its molecular behavior. In this study, we utilize infrared (IR) resonant vacuum ultraviolet photoionization/mass-analyzed threshold ionization (VUV-PI/MATI) mass spectroscopies to capture distinctive vibrational spectra of individual conformers, namely, "twisted" and "bent," within THF. Our conformer-specific vibrational spectra provide valuable insights into the relative populations of these two conformers. The analysis reveals that the twisted (C2) conformer is more stable than the bent (CS) conformer by 17 ± 15 cm-1. By precisely tuning the VUV photon energy to coincide with vibrational excitation via IR absorption, we selectively ionize specific conformers, yielding two-photon IR + VUV-PI/MATI spectra corresponding to the twisted and bent conformers. This investigation conclusively affirms that both the twisted and bent conformers coexist in the neutral state, while only the twisted conformer exists in the cationic state. These findings not only bridge gaps in existing knowledge but also provide profound insights into the behavior of this pivotal molecule in the realms of biology and medicine.

Reactivity of the Intramolecular Vicinal Group-13/P- and B/Group-15-Based Frustrate Lewis Pairs with Sulfur Dioxide: Mechanistic Insight from DFT

The emission of SO2 gas by industrialized societies contributes to the occurrence of acid rain in natural environments. In this study, we put forward a theoretical investigation into the capture reactions of SO2. Our analysis centers on the energy profiles of intramolecular 1,2-cyclohexylene-bridged FLP-associated molecules. We will particularly examine the reactions involving G13/P-based (with G13 denoting Group 13 element) and B/G15-based (with G15 representing Group 15 element) FLP-associated molecules. Except for Tl/P-FLP, B/N-FLP, and B/Bi-FLP, our theoretical examinations indicate that the remaining six FLP-associated molecules, namely G13'/P-FLP (G13' = B, Al, Ga, and In) and B/G15 ' -FLP (G15' = P, As, and Sb), can easily undergo SO2 capture reactions due to their energetic feasibility. Particularly, our theoretical findings suggested that 1,2-cyclohexylene-bridged Al/P-FLP, Ga/P-FLP, B/As-FLP, and B/Sb-FLP are capable of undergoing a reversible reaction and returning to the initial reactant state. Our theoretical evidence indicates that the G13-G15 bond length in the 1,2-cyclohexylene-linked G13/G15-FLP can serve as a basis for evaluating the free activation barrier associated with its reaction with SO2. Two theoretical methods, namely, the frontier molecular orbital theory and the energy decomposition analysis-natural orbitals of chemical valence approach, are utilized to investigate the electronic structure and bonding nature of the reactions under consideration. Moreover, the analyses based on the activation strain model revealed that it is the geometrical deformation energies of G13/G15-FLP, which is the key factor that greatly influences the activation barriers of such SO2 capture reactions. Further, our theoretical computations indicate that such capturing reactions of SO2 by intramolecular 1,2-cyclohexylene-linked G13/G15-based FLP-type molecules obey the Hammond postulate.