ABSOLUTE RATE CONSTANTS FOR HYDROGEN ABSTRACTION FROM ALDEHYDES AND CONFORMATIONAL STUDIES OF THE CORRESPONDING AROMATIC ACYL RADICALS
ABSOLUTE RATE CONSTANTS FOR HYDROGEN ABSTRACTION FROM ALDEHYDES AND CONFORMATIONAL STUDIES OF THE CORRESPONDING AROMATIC ACYL RADICALS
复制标题
DOI：
10.1021/ja00330a036
复制
发表时间：
1984-01-01
影响因子：
15
通讯作者：
PLACUCCI, G
中科院分区：
文献类型：
--
作者：
CHATGILIALOGLU, C;LUNAZZI, L;PLACUCCI, G
用激光闪光光解技术测定了叔丁氧基自由基与有机醛反应的绝对速率常数。在297 K时，EtCHO、C6 H5 CHO、Me 2NCHO和EtOCHO的速率常数分别为8.9、6.8、1.0和0.05 × 107 M ~（-1）s ~（-1）。测定了苯甲醛的Arrhenius参数。极性效应在确定有机醛对叔丁氧基自由基的反应性中是非常重要的。EPR谱描述了一些呋喃甲酰，噻吩甲酰，和吡咯基自由基（阿科）产生的光解在很宽的温度范围内。通过与母体醛的构象异构体的比较，以及溶剂依赖性，检测到构象异构体，并从环质子的超峰分裂的大小获得它们的结构归属。虽然它们是许多化学反应的重要中间体，但关于烷氧基自由基从醛生成它们的绝对速率数据非常有限。事实上，绝对速率数据仅限于一个单一的气相研究H-原子提取的正丁氧基自由基从甲醛和乙醛。1 2在目前的工作中，我们报告了一个动力学研究的形成酰基自由基的反应的叔丁氧基自由基与各种organicaldehyde在溶液中，以及一些酰基自由基的衰减速率，分别通过激光闪光光解和动力学EPR光谱。在此过程中产生的酰基自由基在过去曾被广泛地用电子顺磁共振光谱研究，以阐明其结构和构象。3-7 Davies和Sutcliffe 7最近发现脂肪族酰基自由基的构象行为与母体醛的构象行为相似;他们还表明，在某些自由基中，C-CO键周围存在受限运动。类似地，苯甲酰基自由基被证明是经历了一个限制旋转周围相同的键低于150 K，3 4与一个相对较低的障碍相比，母体分子。8然而，在目前的工作中，
Absolute rate constants for the reactions of rert-butoxyl radicals with some organic aldehydes havebeen measured in solution by using laser flash photolysis techniques. At 297 K, therate constants are 8.9, 6.8, 1.0, and 0.05 X 107 M-1 s-1 for EtCHO, C6H5CHO, Me2NCHO, and EtOCHO, respectively. Arrhenius parameters were determined for benzaldehyde. Polar effects are very important in determining the reactivity of organic aldehydes toward tert-butoxyl radicals. The EPR spectra are described for a number of furoyl, thenoyl, and pyrroyl radicals (ArCO) which were generated photolytically over a wide range of temperatures. Conformational isomers were detected and their structural assignment obtained from the magnitude of the hyperfme splittings of the ring protons, by comparison with the conformers of the parent aldehydes, and from thesolvent dependence.Aldehydes are known to react with a variety of free radicals to form acyl radicals. Although these are important intermediates in many chemical reactions, absolute rate data regarding their formation from aldehydes byalkoxyl radicals are extremely lim-ited. In fact, absolute rate data are restricted to a single gas-phase study of H-atom abstraction by the rm-butoxyl radical from formaldehyde and acetaldehyde. 1 2 In the present work we report a kinetic study of the formation of acyl radicals by the reaction of rert-butoxyl radicals with a variety of organicaldehydes in solution, as well as the rates of decay of some acyl radicals, by laser flash photolysis and kinetic EPR spectroscopy, respectively. The acyl radicals generated by this procedure havebeen ex-tensively studied in the past by means of EPRspectroscopy, in order to elucidate their structure and conformation. 3-7 Davies and Sutcliffe7 recently found that the conformational behavior of aliphatic acyl radicals parallels thatof the parent aldehydes; they also showed that there is restricted motion around the C-CO bond in some of these radicals. Similarly, the benzoyl radical was shown to experience a restricted rotation around the same bond below 150 K, 3 4with a relatively low barrier compared to that of the parent molecule. 8 However, in the present workfurther studies