Laboratory and field measurements have demonstrated that isoprene epoxydiol (IEPOX) is the base component of a wide range of chemical species found in isoprene-derived secondary organic aerosol (SOA). To address newly raised questions concerning the chemical identities of IEPOX-derived SOA, the results of laboratory experiments carried out in bulk aqueous and organic media and analyzed via nuclear magnetic resonance spectroscopy and computed free energies of possible products are reported. The IEPOX nucleophilic addition product 2-methyltetrol was found to react too slowly in aqueous solution to explain the previous observation of tetrahydrofuran-based species. The IEPOX isomerization reactions in organic media were shown to mainly produce 3-methyltetrahydrofuran-2,4-diols, which were also established by the computational results as one of the most thermodynamically favorable possible IEPOX reaction products. However, these isomerization reactions were found to be relatively slow as compared to nucleophilic addition reactions, indicating that their occurrence on ambient SOA might be limited to low water content situations. No evidence was found for the production of the C₅ alkene triols or 3-methyltetrahydrofuran-3,4-diols previously reported for IEPOX reaction on SOA as analyzed via the gas chromatography/electron ionization-quadrupole mass spectrometry with prior trimethylsilyl derivatization method.

中文翻译：

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评估异戊二烯环氧二醇在次级有机气溶胶上的异构化反应的潜在机理

实验室和现场测量表明，异戊二烯环氧二醇（IEPOX）是异戊二烯衍生的次级有机气溶胶（SOA）中发现的多种化学物质的基本成分。为了解决有关IEPOX衍生的SOA的化学特性的新提出的问题，报告了在大量水性介质和有机介质中进行的实验室实验结果，并通过核磁共振波谱进行了分析，并计算了可能产物的自由能。发现IEPOX亲核加成产物2-甲基四醇在水溶液中反应太慢，无法解释先前基于四氢呋喃的物质的观察结果。结果表明，在有机介质中，IEPOX异构化反应主要产生3-甲基四氢呋喃-2,4-二醇，通过计算结果也将其确定为最热力学上可能的IEPOX反应产物之一。但是，发现这些异构化反应与亲核加成反应相比相对较慢，这表明它们在环境SOA上的发生可能仅限于低水含量的情况。没有发现产生C的证据先前报道的_5种烯烃三醇或3-甲基四氢呋喃-3,4-二醇用于SOA上的IEPOX反应，已通过气相色谱/电子电离-四极杆质谱与现有的三甲基甲硅烷基衍生化方法进行了分析。