Department of Physics, University of Helsinki , P.O. Box 64, Helsinki, 00014, Finland.
J Am Chem Soc. 2014 Nov 5;136(44):15596-606. doi: 10.1021/ja507146s. Epub 2014 Oct 21.
The prompt formation of highly oxidized organic compounds in the ozonolysis of cyclohexene (C6H10) was investigated by means of laboratory experiments together with quantum chemical calculations. The experiments were performed in borosilicate glass flow tube reactors coupled to a chemical ionization atmospheric pressure interface time-of-flight mass spectrometer with a nitrate ion (NO3(-))-based ionization scheme. Quantum chemical calculations were performed at the CCSD(T)-F12a/VDZ-F12//ωB97XD/aug-cc-pVTZ level, with kinetic modeling using multiconformer transition state theory, including Eckart tunneling corrections. The complementary investigation methods gave a consistent picture of a formation mechanism advancing by peroxy radical (RO2) isomerization through intramolecular hydrogen shift reactions, followed by sequential O2 addition steps, that is, RO2 autoxidation, on a time scale of seconds. Dimerization of the peroxy radicals by recombination and cross-combination reactions is in competition with the formation of highly oxidized monomer species and is observed to lead to peroxides, potentially diacyl peroxides. The molar yield of these highly oxidized products (having O/C > 1 in monomers and O/C > 0.55 in dimers) from cyclohexene ozonolysis was determined as (4.5 ± 3.8)%. Fully deuterated cyclohexene and cis-6-nonenal ozonolysis, as well as the influence of water addition to the system (either H2O or D2O), were also investigated in order to strengthen the arguments on the proposed mechanism. Deuterated cyclohexene ozonolysis resulted in a less oxidized product distribution with a lower yield of highly oxygenated products and cis-6-nonenal ozonolysis generated the same monomer product distribution, consistent with the proposed mechanism and in agreement with quantum chemical modeling.
通过实验室实验和量子化学计算，研究了环己烯（C6H10）臭氧化过程中高度氧化有机化合物的快速形成。实验在硼硅酸盐玻璃流动管反应器中进行，与化学电离常压接口飞行时间质谱仪耦合，采用基于硝酸盐离子（NO3(-)）的电离方案。量子化学计算在 CCSD(T)-F12a/VDZ-F12//ωB97XD/aug-cc-pVTZ 水平上进行，使用多构象过渡态理论进行动力学建模，包括 Eckart 隧道校正。互补的研究方法提供了一个一致的形成机制的图像，该机制通过过氧自由基（RO2）的异构体化通过分子内氢转移反应推进，随后是顺序的 O2 添加步骤，即 RO2 自氧化，在秒的时间尺度上。过氧自由基的二聚化通过重组和交叉组合反应与高度氧化单体物种的形成竞争，并观察到导致过氧化物，潜在的二酰基过氧化物。从环己烯臭氧化中得到的这些高度氧化产物（单体中 O/C > 1，二聚体中 O/C > 0.55）的摩尔产率为（4.5 ± 3.8）%。完全氘代环己烯和反式-6-壬烯臭氧化，以及向系统中添加水（H2O 或 D2O）的影响，也进行了研究，以加强对所提出机制的论证。氘代环己烯臭氧化导致氧化程度较低的产物分布，高度含氧产物的产率较低，而反式-6-壬烯臭氧化生成相同的单体产物分布，与所提出的机制一致，并与量子化学模拟一致。
