Mancini Luca, Vanuzzo Gianmarco, Recio Pedro, Caracciolo Adriana, Faginas-Lago Noelia, Rosi Marzio, Casavecchia Piergiorgio, Balucani Nadia
Dipartimento di Chimica Biologia e Biotecnologie, Università degli Studi di Perugia, 06123 Perugia, Italy.
Master-Tec Srl, 06128 Perugia, Italy.
J Phys Chem A. 2024 Aug 29;128(34):7177-7194. doi: 10.1021/acs.jpca.4c02924. Epub 2024 Aug 14.
Despite the relevance of the reactions of the prototypical nitrogen-containing six-membered aromatic molecule (N-heterocyclic) of pyridine (CHN) in environmental science, astrochemistry, planetary science, prebiotic chemistry, and materials science, few experimental/theoretical studies exist on the bimolecular reactions involving pyridine and neutral atomic/molecular radicals. We report a combined experimental and theoretical study on the elementary reaction of pyridine with excited nitrogen atoms, N(D), aimed at providing information about the primary reaction products and their branching fractions (BFs). From previous crossed molecular beam (CMB) experiments with mass-spectrometric detection and present synergistic calculations of the reactive potential energy surface (PES) and product BFs we have unveiled the reaction mechanism. It is found that the reaction proceeds via N(D) barrierless addition to pyridine that, via bridged intermediates followed by N atom "sliding" into the ring, leads to 7-membered-ring structures. They further evolve, mainly via ring-contraction mechanisms toward 5-membered-ring radical products and, to a smaller extent, via H-displacement mechanisms toward 7-membered-ring isomeric products and their isomers. Using the theoretical statistical estimates, an improved fit of the experimental data previously reported has been obtained, leading to the following results for the dominant product channels: CHN (pyrrolyl) + HCN (BF = 0.61 ± 0.20), CHN (1H-imidazolyl/1H-pyrazolyl) + CH (BF = 0.11 ± 0.06), and CHN (7-membered-ring molecules or pyrrole carbonitriles) + H (BF = 0.28 ± 0.10). The ring-contraction product channels CHN (pyrrolyl) + HCN, CHN (1H-imidazolyl) + CH, CHN (1H-pyrazolyl) + CH, and CH (cyclopentadienyl) + N have statistical BFs of 0.54, 0.09, 0.11, and 0.07, respectively. Among the H-displacement channels, the cyclic-CHCHCHCHNCN + H channel and cyclic-CHCHCHCHCN + H are theoretically predicted to have a comparable BF (0.07 and 0.06, respectively), while the other isomeric 7-membered-ring molecule + H channel has a BF of 0.03. Pyrrole-carbonitriles and 1H-ethynyl-1H-imidazole (+ H) isomeric channels have an overall BF of 0.03. Implications for the chemistry of Saturn's moon Titan and prebiotic chemistry, as well as for understanding the N-doping of graphene or carbon nanotubes, are noted.
尽管吡啶（CHN）这种典型的含氮六元芳香分子（氮杂环）的反应在环境科学、天体化学、行星科学、前生物化学和材料科学中具有重要意义，但关于吡啶与中性原子/分子自由基的双分子反应的实验/理论研究却很少。我们报告了一项关于吡啶与激发态氮原子N(D)的基元反应的实验与理论相结合的研究，旨在提供有关主要反应产物及其分支比（BFs）的信息。通过先前带有质谱检测的交叉分子束（CMB）实验以及当前对反应势能面（PES）和产物BFs的协同计算，我们揭示了反应机理。研究发现，该反应通过N(D)对吡啶的无势垒加成进行，加成后经由桥连中间体，随后N原子“滑入”环中，形成七元环结构。它们进一步演化，主要通过环收缩机制生成五元环自由基产物，在较小程度上通过氢取代机制生成七元环异构体产物及其异构体。利用理论统计估计，对先前报道的实验数据进行了改进拟合，得出了主要产物通道的以下结果：CHN（吡咯基）+ HCN（BF = 0.61 ± 0.20）、CHN（1H - 咪唑基/1H - 吡唑基）+ CH（BF = 0.11 ± 0.06）以及CHN（七元环分子或吡咯腈）+ H（BF = 0.28 ± 0.10）。环收缩产物通道CHN（吡咯基）+ HCN、CHN（1H - 咪唑基）+ CH、CHN（1H - 吡唑基）+ CH以及CH（环戊二烯基）+ N的统计BFs分别为0.54、0.09、0.11和0.07。在氢取代通道中，理论预测环状 - CHCHCHCHNCN + H通道和环状 - CHCHCHCHCN + H通道具有可比的BF（分别为0.07和0.06），而其他七元环异构体分子 + H通道的BF为0.03。吡咯腈和1H - 乙炔基 - 1H - 咪唑（+ H）异构体通道的总BF为0.03。文中还提到了该研究对土星卫星泰坦的化学和前生物化学的意义，以及对理解石墨烯或碳纳米管的氮掺杂的意义。
