Atmospheric new particle formation is the process by which atmospheric trace gases, typically acids and bases, cluster and grow into potentially climatically relevant particles. Here, we evaluate the structures and structural motifs present in small cationic ammonium and aminium bisulfate clusters that have been studied both experimentally and computationally as seeds for new particles. For several previously studied clusters, multiple different minimum-energy structures have been predicted. Vibrational spectra of mass-selected clusters and quantum chemical calculations allow us to assign the minimum-energy structure for the smallest cationic cluster of two ammonium ions and one bisulfate ion to a CS-symmetry structure that is persistent under amine substitution. We derive phenomenological vibrational frequency scaling factors for key bisulfate vibrations to aid in the comparison of experimental and computed spectra of larger clusters. Finally, we identify a previously unassigned spectral marker for intermolecular bisulfate–bisulfate hydrogen bonds and show that it is present in a class of structures that are all lower in energy than any previously reported structure. Tracking this marker suggests that this motif is prominent in larger clusters as well as ∼180 nm ammonium bisulfate particles. Taken together, these results establish a set of structural motifs responsible for binding of gases at the surface of growing clusters that fully explain the spectrum of large particles and provide benchmarks for efforts to improve structure predictions, which are critical for the accurate theoretical treatment of this process.
Synthesis of α,β-unsaturated-γ-lactams continue to attract attention due to the importance of this structural motif in organic chemistry. Herein, we report the development of a visiblelight-induced excited-state copper-catalyzed [4 + 1] annulation reaction for the preparation of a wide range of γ-H, −OH, and −OR-substituted α,β-unsaturated-γ-lactams using acrylamides as the 4-atom unit and aroyl chlorides as the 1-atom unit. This modular synthetic protocol features mild reaction conditions, broad substrate scope, and high functional group tolerance. The reaction is amenable to late-stage diversification of complex molecular architectures, including derivatives of marketed drugs. The products of the reaction can serve as versatile building blocks for further derivatization. Preliminary mechanistic studies suggest an inner-sphere catalytic cycle involving photoexcitation of the Cu(BINAP) catalyst, single-electron transfer, and capture of radical intermediates by copper species, followed by reductive elimination or protonation to give the desired γ-functionalized α,βunsaturated-γ-lactams.
Heterocycles are one of the largest groups of organic moieties with significant medicinal, chemical, and industrial applications. Herein, we report the discovery and development of visible‐light‐induced, synergistic excited‐state copper catalysis using a combination of Cu(IPr)I as a catalyst and rac‐BINAP as a ligand, which produces more than 10 distinct classes of heterocycles. The reaction tolerates a broad array of functional groups and complex molecular scaffolds, including derivatives of peptides, natural products, and marketed drugs. Preliminary mechanistic investigation suggests in situ generations of [Cu(BINAP)2]+ and [Cu(IPr)2]+ catalysts that work cooperatively under visible‐light irradiation to facilitate catalytic carbo‐aroylation of unactivated alkenes, affording a wide range of useful heterocycles.
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