Hydrocarbon σ‐radical cations

Deciphering the irradiation induced fragmentation-rearrangement mechanisms in valence ionized CF3CH2F

The increasing presence of 1,1,1,2-tetrafluoroethane (CF3CH2F) in the atmosphere has prompted detailed studies into its complex photodissociation behavior. Experiments focusing on CF3CH2F irradiation have unveiled an array of ions, with the persistent observation of the rearrangement product CHF2+ not yet fully understood. In this work, we combine density functional theory, coupled-cluster calculations with a complete basis set formalism, and atom-centered density matrix propagation molecular dynamics to investigate the energetics and dynamics of different potential pathways leading to CHF2+. We found that the two-body dissociation pathway involving an HF rearrangement, which was previously considered complex for CHF2+ formation, is actually straightforward but not likely due to the facile loss of HF. In contrast, our calculations reveal that the H elimination pathway, once thought of as a potential route to CHF2+, is not only comparably disadvantageous from both thermodynamic and kinetic points of view but also does not align with experimental data, particularly the lack of a rebound peak at m/z 101-102. We establish that the formation of CHF2+ is predominantly via the HF elimination channel, a conclusion experimentally corroborated by studies involving the trifluoroethylene cation CF2CHF+, a key intermediate in this process.

Selective C-H Activation of Molecular Nanodiamonds via Photoredox Catalysis

While substituted adamantanes have widespread use in medicinal chemistry, materials science, and ligand design, the use of diamantanes and higher diamondoids is limited to a much smaller number. Selective functionalization beyond adamantane is challenging, as the number of very similar types of C-H bonds (secondary, 2°, and tertiary, 3°) increases rapidly, and H atom transfer does not provide a general solution for site selectivity. We report a method using pyrylium photocatalysts that is effective for nanodiamond functionalization in up to 84% yield with exclusive 3° selectivity and moderate levels of regioselectivity between 3° sites. The proposed mechanism involving photooxidation, deprotonation, and radical C-C bond formation is corroborated through Stern-Volmer luminescence quenching, cyclic voltammetry, and EPR studies. Our photoredox strategy offers a versatile approach for the streamlined synthesis of diamondoid building blocks.

Endohedral σ-Diradical Nitrogen-Vacancy Diamond Nanoclusters with a Confined Magnetic Space and Strong Electronic Spin Couplings

The electronic properties and their modulations for the nitrogen-vacancy (NV) centers in various nanoscale diamonds are of profound current interest because of their potential applications. However, although the NV centers as chromophores in diamond are the most widely studied, surprisingly, little is known about their magnetic spin coupling properties up to now. Here, we for the first time show, using the spin-polarized DFT calculations, that the NV centers can act as unique endohedral σ-diradical magnets in diamond nanoclusters and exhibit quite strong ferromagnetic (FM) or antiferromagnetic (AFM) spin coupling characteristics due to their unique endotetrahedral structures with favorable radical-radical contacts. Although the neutral NV center (NV⁰) in its doublet ground state exhibits quite strong AFM spin coupling among three radical C-sites (i.e., an AFM triradical center), interestingly, excess electron injection can convert it to a FM diradical magnet (i.e., the triplet ground state NV^-) with almost unchanged J-coupling magnitude, and the J-coupling of the nanocluster can be noticeably enhanced by F-termination of the surface due to triradical spin delocalization mediated by excess electron. However, interior modification (one C in the endotetrahedron core is substituted by N or B or is hydrogenated) can assign the nanocluster perfect AFM diradical character. The spin coupling strength presents a quasilinear correlation with the distance between the two C radicals in the NV core for the same size of the clusters and a high linear correlation with the energy difference between two singly occupied molecular orbitals. Clearly, the FM and AFM couplings as well as their switching behavior in such NV defect diamond nanoclusters featuring the endohedral σ-diradicals are a novel type of promising magnetic material motifs. These findings open up promising spintronic application prospects of the NV diamonds and provide helpful information for the design of inorganic magnetic materials and logic devices.

Catalyzed and Promoted Aliphatic Fluorination

In the last six years, the direct functionalization of aliphatic C-H (and C-C) bonds through user-friendly, radical-based fluorination reactions has emerged as an exciting research area in fluorine chemistry. Considering the historical narratives about the challenges of developing practical radical fluorination in organic frameworks, notable advancements in controlling both reactivity and selectivity have been achieved during this time. As one of the participants in the field, herein, we a provide brief account of research efforts in our laboratory from the initial discovery of radical monofluorination on unactivated C-H bonds in 2012 to more useful strategies to install fluorine on biologically relevant molecules through directed fluorination methods. In addition, accompanying mechanistic studies that have helped guide reaction design are highlighted in context.

Cation States of Ethane: HEAT Calculations and Vibronic Simulations of the Photoelectron Spectrum of Ethane

High-accuracy ab initio calculations have been carried out on ethane and its radical cation. With the HEAT-345(Q) scheme, adiabatic ionization potentials of 11.52 and 11.57 eV are determined for the X̃ (2)Eg and à (2)A1g states, respectively, with an uncertainty of ±0.015 eV. Also considered in this report are linear and quadratic vibronic coupling involving both states. With this simple vibronic model, the photoelectron spectrum of ethane was simulated in the 11-15 eV region using linear and full quadratic Jahn-Teller coupling Hamiltonians, and with up to 70 billion direct product basis functions in a high-performance computing environment. Although the linear vibronic coupling model adequately reproduces the spectral envelope, the quadratic vibronic treatment results in much better agreement with the observed spectrum.