✍ Scribed by G. Navon; M. Polak
No coin nor oath required. For personal study only.
T, relaxation of one set of nuclei causes an extra-broadening and an apparent reduction of the spin-spin splitting in the NMR spectrum of another set of nuclei coupled to it. These effects are demonstrated by lime-shape calculations for first order multiplets of spin l/2 nuclei. It is shown that in a well-resolved multiplet of nuclei A in A, X,, spectra the extra-broadening of each component is given by n/2T,~. During our &dies on the effect of dissolved oxygen on NMR line shapes of organic molecules [l] we have noticed that while singlet absorption lines of all molecules were broadened almost equally, spin-spin multiplets (A, X,) exhibited extra-broadening
in the increasing order of doublets < triplets < quartets. The broadenings were in the constant ratios of 1: 1.9:Z.S for singlets, triplets and quartets, respectively. In addition, an apparent decrease in the spin-spin splitting was found to follow the line broadening.
Since the effect of oxygen was equal for all organic molecules, we concluded that both phenomena resulted from a T1 spin-decoupling effect whereby a T, relaxation process of a group of nuclei (X) produces a process analogous to chemical exchange among the various lines of the spin-spin multiplet of nuclei (A) coupled to it. While in our case both Tt and T2 relaxation processeswere produced by the pammagnetic oxygen molecules; the effect on the spectral line shape is more general. This effect leads to an extra broadening, in addition to that due to the direct T2 processes, and to an apparent collapse of the spin-spin splitting_ Such phenomena
📜 SIMILAR VOLUMES
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