Differential Tunneling‐Driven and Vibrationally‐Induced Reactivity in Isomeric Benzazirines

Nunes, Cláudio M.; Doddipatla, Srinivas; Loureiro, Graça; Roque, José P. L.; Pereira, Nelson M. A.; Melo, Teresa M. V. D. Pinho e; Fausto, Rui

doi:10.1002/chem.202202306

Cited by 8 publications

(1 citation statement)

References 64 publications

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“…After deposition, the temperature was decreased to 15 K and kept at this temperature both during IR spectrum measurements and UV irradiation. In previous studies from our group, 35,36 we observed that in Kr matrices the OH stretching bands are frequently less prone to broadening and splitting than in Ar matrices; therefore, the probability to obtain better resolved spectra increases. This justifies our choice for krypton as matrix gas instead of the most commonly used argon.…”

Section: Experimental Methodsmentioning

confidence: 70%

Breaking and Formation of Intramolecular Hydrogen Bonds in Dihydroxybenzaldehydes through UV-Induced Conformational Changes in a Low-Temperature Matrix

et al. 2022

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Hydrogen bonding (HB) has been receiving attention from both experimental and theoretical researchers since its discovery in the 1920s due to its impact on many chemical and biological processes. However, despite the large number of investigations conducted on this topic, the nature of the HBs and, in particular, the estimation of intramolecular HB energies are still very active subjects of research. In this context, here we report a matrix isolation infrared spectroscopy study of 2,3-dihydroxybenzaldehyde (2,3-DHBA) and 2,4-dihydroxybenzaldehyde (2,4-DHBA), which contain two [one resonance-assisted HB (RAHB) and one conventional HB] and one (RAHB) intramolecular hydrogen bonds, respectively, in their most stable conformer. After isolation of the compounds in cryogenic (15 K) krypton matrices, ultraviolet irradiation led to the formation of higher-energy conformers (by a 180°rotation of the hydroxyl and aldehyde groups), which implies breaking of the intramolecular HBs initially existing in the isolated species and, in the case of 2,3-DHBA, to the formation of a new intramolecular HB. In this way, we were able to manipulate the structure of the molecules, allowing to characterize a diversity of intramolecular HBs in which the OH groups participate (from strong intramolecular RAHBs to weaker conventional HBs, and also no intramolecular HBs) through the corresponding vibrational signatures. The spectroscopic studies were complemented by natural bond orbital analysis and the molecular tailoring approach method, in order to estimate the relative intramolecular HB energies and explore the substitution effects on HB strength.

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Section: Experimental Methodsmentioning

confidence: 70%

Breaking and Formation of Intramolecular Hydrogen Bonds in Dihydroxybenzaldehydes through UV-Induced Conformational Changes in a Low-Temperature Matrix

et al. 2022

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Competitive Heavy‐Atom Tunneling Reactions Controlled Through Electronic Effects

Roque,

Nunes,

Saito

et al. 2024

ChemistryEurope

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Controlling QMT reactivity remains exceptionally challenging and largely unexplored, as it requires rationales distinctly different from those used for classical chemical reactivity. Herein, we investigated how QMT reactivity can be controlled using electronic substituent effects. Benzazirines, which have the exceptional feature to react via two competitive QMT pathways, were used as model compounds. Three novel derivatives with increasingly stronger electron‐donating substituents at C4 [R = OH, N(CH3)2, and N(CH2)4] were generated in argon matrices at 3 K. Remarkably, different QMT selectivities were observed in all benzazirines. As the electron‐donating strength of the substituent increases, the QMT ring‐opening to nitrene starts to compete with the QMT ring‐expansion to ketenimine, becoming the dominant process for the strongest electron‐donating substituent [N(CH2)4]. A theoretical analysis of the substituent effects on the QMT reactivity of benzazirines was performed and compared with the experimental data for these and other C4 derivatives. Overall, the results compellingly demonstrate how subtle changes in electronic effects can be used to fine‐tune QMT selectivity.

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Differential Tunneling‐Driven and Vibrationally‐Induced Reactivity in Isomeric Benzazirines

Nunes

Doddipatla

Loureiro

et al. 2022

Chemistry A European J

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Quantum mechanical tunneling of heavy-atoms and vibrational excitation chemistry are unconventional and scarcely explored types of reactivity. Once fully understood, they might bring new avenues to conduct chemical transformations, providing access to a new world of molecules or ways of exquisite reaction control. In this context, we present here the discovery of two isomeric benzazirines exhibiting differential tunneling-driven and vibrationally-induced reactivity, which constitute exceptional results for probing into the nature of these phenomena. The isomeric 6-fluoro-and 2fluoro-4-hydroxy-2H-benzazirines (3-a and 3'-s) were generated in cryogenic krypton matrices by visible-light irradiation of the corresponding triplet nitrene 3 2-a, which was produced by UV-light irradiation of its azide precursor. The 3'-s was found to be stable under matrix dark conditions, whereas 3-a spontaneously rearranges (τ 1/2 ~64 h at 10 and 20 K) by heavy-atom tunneling to 3 2-a. Near-IR-light irradiation at the first OH stretching overtone frequencies (remote vibrational antenna) of the benzazirines induces the 3'-s ring-expansion reaction to a seven-member cyclic ketenimine, but the 3-a undergoes 2H-azirine ring-opening reaction to triplet nitrene 3 2-a. Computations demonstrate that 3-a and 3'-s have distinct reaction energy profiles, which explain the different experimental results. The spectroscopic direct measurement of the tunneling of 3-a to 3 2-a constitutes a unique example of an observation of a species reacting only by nitrogen tunneling. Moreover, the vibrationally-induced sole activation of the most favorable bond-breaking/bond-forming pathway available for 3-a and 3'-s provides pioneer results regarding the selective nature of such processes.

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Differential Tunneling‐Driven and Vibrationally‐Induced Reactivity in Isomeric Benzazirines

Cited by 8 publications

References 64 publications

Breaking and Formation of Intramolecular Hydrogen Bonds in Dihydroxybenzaldehydes through UV-Induced Conformational Changes in a Low-Temperature Matrix

Breaking and Formation of Intramolecular Hydrogen Bonds in Dihydroxybenzaldehydes through UV-Induced Conformational Changes in a Low-Temperature Matrix

Competitive Heavy‐Atom Tunneling Reactions Controlled Through Electronic Effects

Differential Tunneling‐Driven and Vibrationally‐Induced Reactivity in Isomeric Benzazirines

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