Franzon Lauri, Savolainen Anni, Iyer Siddharth, Rissanen Matti, Kurtén Theo
Department of Chemistry, University of Helsinki, P.O. Box 55 (A.I. Virtasen aukio 1), 00014 Helsinki, Finland.
Aerosol Physics Laboratory, Physics Unit, Tampere University, 33720 Tampere, Finland.
Phys Chem Chem Phys. 2025 Jun 11;27(23):12198-12210. doi: 10.1039/d5cp01175b.
Acyl peroxy radicals are especially efficient at forming organic accretion products in the troposphere, but they also have short lifetimes due to rapid unimolecular reactions. For this reason, we find it important to accurately represent the reactions of these species in structure-activity relationships estimating the unimolecular reactivity of atmospheric peroxy radicals. To address this, we performed multi-conformer transition state theory calculations to determine H-shift and ring closure reaction rates for aldehyde-substituted and unsaturated acyl peroxy radicals over a wide temperature range. Similar calculations were performed for enol-substituted peroxy radicals, which are also underrepresented in SAR models. As a results, we found that H-shifts from aldehyde groups are highly competitive, that ring closures are overwhelmingly the major atmospheric fate of unsaturated acyl peroxy radicals, and that H-shifts from -enols outcompete all other unimolecular and bimolecular reactions whenever they are possible. In conclusion, in extending the SAR models we have gained valuable insight on some of the most rapid reactions for any peroxy radicals in the atmosphere.
酰基过氧自由基在对流层中形成有机积聚产物的效率特别高，但由于快速的单分子反应，它们的寿命也很短。因此，我们发现在估计大气过氧自由基单分子反应活性的构效关系中准确描述这些物种的反应非常重要。为了解决这个问题，我们进行了多构象过渡态理论计算，以确定醛取代和不饱和酰基过氧自由基在很宽温度范围内的氢转移和闭环反应速率。对烯醇取代的过氧自由基也进行了类似的计算，烯醇取代的过氧自由基在构效关系模型中也未得到充分体现。结果，我们发现醛基的氢转移竞争非常激烈，闭环反应绝大多数情况下是不饱和酰基过氧自由基在大气中的主要归宿，并且只要有可能，烯醇的氢转移比所有其他单分子和双分子反应都更具竞争力。总之，在扩展构效关系模型时，我们对大气中任何过氧自由基的一些最快速反应有了宝贵的见解。
