Efficient NMR Pulse Sequences to Transfer the Parahydrogen-Induced Polarization to Hetero Nuclei

The PASADENA or PHIP effect originates from the breakdown of the parahydrogen symmetry when the two protons are found in magnetically inequivalent positions after hydrogenation. As a result, a signal enhancement of up to 10 4 in the proton NMR spectra can be observed. We introduce three polarization transfer techniques, namely PH-INEPT, PH-INEPT+, and INEPT(+π/4), that are highly effective to record in situ hetero NMR spectra of parahydrogen-labeled compounds. A complete product operator treatment as well as experimental results for 13 C and 29 Si have been given. With these sequences we obtained a signal enhancement of 500 which allows in situ NMR investigations of hetero nuclear systems at natural abundance.