Nitroxide paramagnet-induced para-ortho conversion and nuclear spin relaxation of H2 in organic solvents

Journal of the American Chemical Society
Elena SartoriNicholas J Turro

Abstract

The kinetics of para-ortho conversion and nuclear spin relaxation of H 2 in chloroform- d 1 were investigated in the presence of nitroxides as paramagnetic catalysts. The back conversion from para-hydrogen ( p-H 2) to ortho-hydrogen ( o-H 2) was followed by NMR by recording the increase in the intensity of the signal of o-H 2 at regular intervals of time. The nitroxides proved to be hundreds of times more effective at inducing relaxation among the spin levels of o-H 2 than they are in bringing about transitions between p-H 2 and the levels of o-H 2. The value of the encounter distance d between H 2 and the paramagnetic molecule, calculated from the experimental bimolecular conversion rate constant k 0, using the Wigner theory of para-ortho conversion, agrees perfectly with that calculated from the experimental relaxivity R 1 using the force free diffusion theory of spin-lattice relaxation.

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Citations

Jul 21, 2012·Journal of the American Chemical Society·Alfonso ZoleoNicholas J Turro
Apr 20, 2011·Physical Chemistry Chemical Physics : PCCP·Michael C D Tayler, Malcolm H Levitt
Aug 7, 2013·Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences·Malcolm H Levitt
Jan 10, 2012·Annual Review of Physical Chemistry·Malcolm H Levitt
Nov 5, 2014·Physical Chemistry Chemical Physics : PCCP·Grygoriy A Dolgonos, Gilles H Peslherbe
Dec 22, 2015·Physical Chemistry Chemical Physics : PCCP·Salvatore MamoneAnthony J Horsewill
Sep 4, 2019·Chemphyschem : a European Journal of Chemical Physics and Physical Chemistry·Andreas B SchmidtJan-Bernd Hövener

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