SYMMETRY BREAKDOWN DURING PARAHYDROGEN LABELING OF SYMMETRICAL SUBSTRATES - PROTON SPIN POLARIZATION AND SINGLET/TRIPLET MIXING DUE TO C-13-ISOTOPES IN NATURAL-ABUNDANCE
SYMMETRY BREAKDOWN DURING PARAHYDROGEN LABELING OF SYMMETRICAL SUBSTRATES - PROTON SPIN POLARIZATION AND SINGLET/TRIPLET MIXING DUE TO C-13-ISOTOPES IN NATURAL-ABUNDANCE
复制标题
DOI：
10.1021/j100049a012
复制
发表时间：
1995-12-07
影响因子：
--
通讯作者：
BARGON, J
中科院分区：
文献类型：
--
作者：
HAAKE, M;BARKEMEYER, J;BARGON, J
质子自旋极化不仅发生在用仲氢（p-Hz）氢化不对称取代的乙炔的过程中，而且发生在对称烃底物的氢化过程中：天然丰度的C-13-同位素即使在看似对称的产物中也会导致不对称，并打破前p-H-2质子的磁对称性。氢化产物的极化模式敏感地依赖于催化反应中间体中的核单重态/三重态（S/T-0）混合程度。取决于底物的性质，阳离子催化剂使底物具有不同程度的S/T-0混合，从而产生关于催化反应机理的信息。在乙炔二羧酸对称二酯的氢化过程中，也检测到了仅含C-12-同位素的产物的意想不到的极化信号。这些信号反映了一个不寻常的核自旋人口尚未未知的来源，他们的解释需要现有的理论模型的增强。
Proton spin polarization occurs not only during the hydrogenation of asymmetrically substituted acetylenes with parahydrogen (p-Hz) but also during the hydrogenation of symmetric hydrocarbon substrates: C-13-isotopes in natural abundance cause asymmetry even in seemingly symmetric products and break the magnetic symmetry of the former p-H-2 protons. The polarization patterns of the hydrogenated products sensitively depend on the degree of nuclear singlet/triplet (S/T-0) mixing in the intermediates of the catalytic reactions. Depending on the nature of the substrate, cationic catalysts hydrogenate substrates with different degrees of S/T-0 mixing, thereby yielding information about the catalytic reaction mechanisms. During the hydrogenation of symmetric diesters of acetylene dicarboxylic acid, unexpected polarization signals of products containing only C-12-isotopes have also been detected. These signals reflect an unusual nuclear spin population of yet unknown origin; their explanation demands an augmentation of the existing theoretical models.