Combined ESR and thermodynamic studies of the superoxide adduct of 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide (DEPMPO): hindered rotation around the O-O bond evidenced by two-dimensional simulation of temperature-dependent spectra.
Combined ESR and thermodynamic studies of the superoxide adduct of 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide (DEPMPO): hindered rotation around the O-O bond evidenced by two-dimensional simulation of temperature-dependent spectra.
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5-(二乙氧基磷酰基)-5-甲基-1-吡咯啉 N-氧化物 (DEPMPO) 超氧化物加合物的 ESR 和热力学联合研究：温度相关光谱的二维模拟证明了绕 O-O 键的旋转受阻。
DOI：
10.1021/jp070679u
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
S. Pietri
中科院分区：
文献类型：
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作者：
A. Rockenbauer;J. Clément;M. Culcasi;A. Mercier;P. Tordo;S. Pietri
DEPMPO-OOH是5-（二乙氧基磷酰基）-5-甲基-1-吡咯啉N-氧化物（DEPMPO）的超氧化物加合物，其主要非对映异构体（1）的ESR谱中出现超精细结构和线宽变化（LWA），本文通过实验研究了这种结构的起源。使用选择性氘代DEPMPO衍生物，我们证明了超超精细图案可以明确地归因于远程耦合。在吡啶中记录宽温度范围内的高分辨光谱，结合二维模拟，使我们能够表征1中的倒置LWA，并揭示了次要DEPMPO-OOH非对映异构体（2）光谱中的均匀谱线增宽，这两种效应都源于构象异构体之间的化学交换。当模拟1在快速交换制度中呈现LWA的各个光谱时，获得了四个同样良好的拟合，并且可以通过使用二维模拟技术来解决这种模糊性。该交换的热力学和动力学常数与围绕O-O键的旋转一致。我们建议，线加宽效应1和2的结果从这个O-O旋转与吡咯烷环的赝旋转相一致。
Experiments were performed to elucidate the origin of the superhyperfine structure and line width alternation (LWA) seen in the ESR spectrum of the major diastereoisomer (1) of DEPMPO-OOH, the remarkably persistent superoxide adduct of 5-(diethoxyphosphoryl)-5-methyl-1-pyrroline N-oxide (DEPMPO). Using selectively deuterated DEPMPO derivatives, we demonstrated that the superhyperfine pattern can be unambiguously attributed to long-range couplings. The recording in pyridine of highly resolved spectra in a wide temperature range, combined with two-dimensional simulation, allowed us to characterize an inverted LWA in 1 and revealed a uniform line broadening in the spectrum of the minor DEPMPO-OOH diastereoisomer (2), with both effects originating from a chemical exchange between conformers. When the individual spectra of 1 presenting LWA in the fast-exchange regime were simulated, four equally good fits were obtained and this ambiguity could be resolved by using a two-dimensional simulation technique. The thermodynamic and kinetic constants of this exchange were consistent with a rotation around the O-O bond. We propose that line broadening effects in 1 and 2 result from this O-O rotation concerted with the pseudo-rotation of the pyrrolidine ring.