This research reveals the reaction mechanism of pyridinyl radicals with acrylonitrile, suggesting low bicyclic compound yields, highlighting challenges in radical chemistry.
In this study, we tackle the challenge of synthesizing nitrogen-containing bicyclic compounds in the gas phase, a topic of considerable interest to interstellar chemistry and combustion science. We specifically explore the bimolecular reaction between the o-pyridinyl radical (C5H4N•), a quintessential nitrogen-containing monocyclic carbon-centered aromatic radical, and the interstellar molecule acrylonitrile (C3H3N) in a resistance-heated silicon carbide (SiC) microreactor. Utilizing advanced molecular beam-sampled synchrotron VUV photoionization mass spectrometry (SVUV-PIMS), we detected the formation of C8H6N2 species at 1100 K. Photoionization efficiency (PIE) curve analysis suggested the exclusive production of a ring-tail structure, rather than the desired bicyclic 1,5-naphthyridine structure. High-level ab initio calculations revealed a detailed reaction mechanism that addition, cyclization, and subsequent dehydrogenation reactions between C5H4N• and C3H3N can lead to the formation of either 3-(2-pyridinyl)-2-propenenitrile or 1,5-naphthyridine. However, the formation of 1,5-naphthyridine under the present experimental conditions was not efficient, as supported by rate coefficient calculations. The complex mechanisms of radical-neutral reactions were revealed in this work, guiding the gas-phase synthesis of nitrogen-containing aromatic compounds.
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Liu et al. (2025) studied this question.
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