Intensities in NMR spectra

Herzfeld J, Berger AE (1980) Sideband intensities in NMR spectra of samples spinning at the magic angle J Chem Phys 73 6021-6030... 

As stated above, CIDNP denotes the transient occurrence of anomalous line intensities in NMR spectra recorded during chemical reactions or shortly after their completion. The phenomenon was first observed in 1967 by Bargon, Fischer and Johnsen [35a] in thermal decompositions of peroxides and azo compounds, and, independently, by Ward and Lawler [35b] in the reactions of alkyl lithium with alkyl halides. It was immediately realized that the line anomalities are caused by populations of the nuclear spin states in the reaction products that deviate from the Boltzmann populations. After initial attempts of interpreting CIDNP by electron-nuclear cross-relaxation, the radical pair mechanism was developed in 1969 by Kaptein and Oosterhoff [36a], and independently by Closs [36b],... 

The distribution of structural units depends exclusively on the contribution of comonomers to the copolymer chain. Experimental average lengths of lactidyl and glycolidyl blocks can be calculated from the relative intensity of the signals corresponding to different diad sequences assigned in NMR spectra (Fig. 32) and from the equations (1) and (2) (/ql-gl, f GL-LA, and /la gl are the... 

The carbon skeleton of an organic compound can be derived by measurement of one-bond 13C—13C coupling constants, because identical Jcc values found for two carbon atoms identify their connectivity (Section 2.9.4.). However, homonuclear carbon multiplets are usually lost in the noise when 13C NMR spectra of samples with naturally abundant 13C are recorded. Only in strong solutions or neat liquid samples of smaller molecules can CC multiplets be observed as weak satellites (0.5% of the normal carbon-13 signal intensity) in NMR [133], Otherwise, 13C enriched samples must... 

Unlike H NMR spectra, whose integration of signals represents the ratio of protons, integration of 13C peaks do not correlate with the ratio of carbon atoms in routine spectra. There are two major factors that account for the problem of peak intensities in 13C spectra ... 

More recently an elegant solution to the problem of getting well defined multiplets in NMR spectra, under conditions of partial proton decoupling, has been devised. (161) This is known as J-scaling and leads to spectra in which all multiplet components have their normal intensities but all the splittings are reduced by any desired factor which is the same for each carbon. Typically a scaling factor of 30 is found convenient since then the residual one-bond H splittings... 

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