Parahydrogen Induced Polarization and In Situ Spectroscopy

Consequently, in PHIP spectra both doublets and triplets only exhibit two lines, since the central line of the triplet has an intensity of zero. This phenomenon has to be taken into account appropriately when analyzing PHIP spectra, since the size of the J-coupling constants might otherwise easily be misjudged by a factor of two  

In addition, it is important to note that the phase behavior of PHIP NMR signals differs substantially from that in standard NMR experiments. For normal NMR spectroscopy, a 90° pulse renders the maximum possible signal intensity, while a 180° pulse gives no intensity at all. This is not true for PHIP spectra In PHIP NMR, the maximum signal intensity is achieved by a 45° pulse a 90° pulse is here the zero-crossing (like 180° in standard NMR, yielding minimum intensity). 

The occurrence of polarization signals during homogeneous hydrogenations can be regarded as proof of the transfer of both atoms of the former parahydrogen molecule, that is, they become transferred as a pair or in a pair-wise maimer. 

This process does not necessarily have to be simultaneous, but the two atoms of the dihydrogen molecule must retain a spin-spin coupling throughout the whole process. Conversely, if they are not transferred pair-wise (i. e., if the transferred hydrogen atoms stem from different dihydrogen molecules or if they lose their coupling in the course of the process), no polarization can be detected. 

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