Tsang Wing
National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
J Phys Chem A. 2006 Jul 13;110(27):8501-9. doi: 10.1021/jp058125j.
This paper is concerned with the mechanisms and rate constants for the decomposition of 1-penten-3-yl, 1-penten-4-yl, and 1-penten-5-yl radicals. They are formed from radical attack on 1-pentene, which is an important decomposition product of normal alkyl radicals with more than 6 carbon atoms in combustion systems. This work is based on related data in the literature. These involve rate constants for the reverse radical addition process under high-pressure conditions, chemical activation experiments, and more recent direct studies. The high-pressure rate constants are based on detailed balance. The energy transfer effects and the pressure dependences of the rate constants are determined through the solution of the master equation and are projected to cover combustion conditions. The low barriers to these reactions make it necessary to treat these thermal reactions as open systems, as in chemical activation studies. The multiple reaction channels make the nature of the pressure effects different from those usually described in standard texts. The order of stability is 1-penten-3-yl approximately 1-penten-4-yl > 1-penten-5-yl and straddles those for the n-alkyl radicals. A key feature in these reactions is the effects traceable to allylic resonance. However, the 50 kJ/mol allylic resonance energy is not fully manifested. The important unsaturated products are 1,3-butadiene, the pentadienes, allyl radicals, and vinyl radicals. The results are compared with the recommendations in the literature, and significant differences are noted. Extensions to larger radicals with similar structures are discussed.
本文关注1-戊烯-3-基、1-戊烯-4-基和1-戊烯-5-基自由基的分解机制和速率常数。它们由自由基对1-戊烯的攻击形成，1-戊烯是燃烧系统中碳原子数超过6的正烷基自由基的重要分解产物。这项工作基于文献中的相关数据。这些数据包括高压条件下自由基加成逆过程的速率常数、化学活化实验以及最近的直接研究。高压速率常数基于细致平衡。通过求解主方程确定能量转移效应和速率常数的压力依赖性，并预计其涵盖燃烧条件。这些反应的低势垒使得有必要像在化学活化研究中那样将这些热反应视为开放系统。多个反应通道使得压力效应的性质不同于标准文献中通常描述的情况。稳定性顺序为1-戊烯-3-基≈1-戊烯-4-基＞1-戊烯-5-基，且跨越了正烷基自由基的稳定性顺序。这些反应的一个关键特征是可追溯到烯丙基共振的效应。然而，50 kJ/mol的烯丙基共振能并未完全体现出来。重要的不饱和产物是1,3-丁二烯、戊二烯、烯丙基自由基和乙烯基自由基。将结果与文献中的建议进行了比较，并指出了显著差异。还讨论了对具有类似结构的更大自由基的扩展。
