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Gas-Phase Formation and Isomerization Reactions of Cyanoacetaldehyde, a Prebiotic Molecule of Astrochemical Interest
ACS Earth and Space Chemistry ( IF 2.9 ) Pub Date : 2021-05-11 , DOI: 10.1021/acsearthspacechem.1c00013 Bernardo Ballotta 1 , Surajit Nandi 1 , Vincenzo Barone 1, 2 , Sergio Rampino 1, 2
ACS Earth and Space Chemistry ( IF 2.9 ) Pub Date : 2021-05-11 , DOI: 10.1021/acsearthspacechem.1c00013 Bernardo Ballotta 1 , Surajit Nandi 1 , Vincenzo Barone 1, 2 , Sergio Rampino 1, 2
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Cyanoacetaldehyde (NC–CH2CH═O) is considered, together with guanidine and urea, as a precursor of the pyrimidine bases cytosine and uracil. Although it has not yet been detected in the interstellar medium (ISM), several hypotheses have been put forward about its synthesis in solution and in the gas phase. In this paper, we present a gas-phase model of the barrierless reaction between formyl (HCO) and cyanomethyl (CH2CN) radicals leading to cyanoacetaldehyde and focus on its evolution through isomerization and dissociation pathways. The potential-energy surface for all reactions has been explored by DFT calculations employing double-hybrid functionals and further refined through the “Cheap” composite scheme. Our results indicate that the direct association of the two reacting radicals (HCO and CH2CN) is strongly exothermic and thus thermodynamically favored under the harsh conditions of the ISM. Microcanonical rate constants computed with the help of the StarRate program for energies up to 6 kJ mol–1 above the dissociation limit show that the most abundant products are the two conformers of cyanoacetaldehyde (nitrile and carbonyl groups in a cis or trans configuration) which, despite having comparable stability, are obtained with a cis/trans ratio of 0.35:0.65. The formation of other products with relative abundances not exceeding 10% is also discussed.
中文翻译：
氰基乙醛的气相形成和异构化反应
氰基乙醛（NC-CH 2 CH = O）与胍和尿素一起被认为是嘧啶碱基胞嘧啶和尿嘧啶的前体。尽管尚未在星际介质（ISM）中检测到它，但已提出了关于在溶液和气相中合成的几种假设。在本文中，我们提出了甲酰基（HCO）与氰基甲基（CH 2CN）自由基会导致氰基乙醛，并专注于其通过异构化和解离途径的演变。通过使用双杂化功能的DFT计算，已经探索了所有反应的势能表面，并通过“便宜”复合方案对其进行了进一步完善。我们的结果表明，两个反应自由基（HCO和CH 2 CN）的直接缔合强烈放热，因此在ISM的苛刻条件下热力学上受到青睐。在StarRate程序的帮助下，对于能量高达6 kJ mol –1的微规范速率常数进行了计算高于解离极限表明，最丰富的产物是氰基乙醛的两个构象异构体（顺式或反式构型的腈和羰基），尽管具有相当的稳定性，但顺式/反式比例为0.35：0.65。还讨论了相对丰度不超过10％的其他产品的形成。
更新日期：2021-05-20
中文翻译：
氰基乙醛的气相形成和异构化反应
氰基乙醛（NC-CH 2 CH = O）与胍和尿素一起被认为是嘧啶碱基胞嘧啶和尿嘧啶的前体。尽管尚未在星际介质（ISM）中检测到它，但已提出了关于在溶液和气相中合成的几种假设。在本文中，我们提出了甲酰基（HCO）与氰基甲基（CH 2CN）自由基会导致氰基乙醛，并专注于其通过异构化和解离途径的演变。通过使用双杂化功能的DFT计算，已经探索了所有反应的势能表面，并通过“便宜”复合方案对其进行了进一步完善。我们的结果表明，两个反应自由基（HCO和CH 2 CN）的直接缔合强烈放热，因此在ISM的苛刻条件下热力学上受到青睐。在StarRate程序的帮助下，对于能量高达6 kJ mol –1的微规范速率常数进行了计算高于解离极限表明，最丰富的产物是氰基乙醛的两个构象异构体（顺式或反式构型的腈和羰基），尽管具有相当的稳定性，但顺式/反式比例为0.35：0.65。还讨论了相对丰度不超过10％的其他产品的形成。
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