Spin multiplicity, chemical conventions

In this article it has been shown, that the low temperature photopolymerization reaction of diacetylene crystals is a highly complex reaction with a manifold of different reaction intermediates. Moreover, the diacetylene crystals represent a class of material which play a unique role within the usual polymerization reactions conventionally performed in the fluid phase. The spectroscopic interest of this contribution has been focussed mainly on the electronic properties of the different intermediates, such as butatriene or acetylene chain structure, diradical or carbene electron spin distributions and spin multiplicities. The elementary chemical reactions within all the individual steps of the polymerization reaction have been successfully investigated by the methods of solid state spectroscopy. Moreover we have been able to analyze the physical and chemical primary and secondary processes of the photochemical and thermal polymerization reaction in diacetylene crystals. This success has been largely due to the stability of the intermediates at low temperatures and to the high informational yield of optical and ESR spectroscopy in crystalline systems. 

Figure 12 Using the conventional delay d2 = 1/2/ results in false coherences relating the 1 spin to the sums or differences of the frequencies of the S spins, and intensity distortions. In the worst case this can result in an HMQC spectrum in which only coherences resulting from multiple S spin transitions are seen. Inverse detected HMQC Cl Rh NMR spectrum of [Rh6(CO)i5 P(C6H4F)3 ] left unconventional mixing time = 1 /(5/) gives single spin Rh transitions only, correlations appear at the correct Sju, ri t, conventional mixing time = 1 /(2/), gives multiple Rh spin transitions . Only ONE of these transitions occurs at a Rh chemical shift...

The conventional spin-echo experiments, both in the single-pulse refocusing (Carr-Purcell) and multiple-pulse refocusing (CPMG) version, remove the field inhomogeneity, chemical shift and heteronuclear coupling effects, but not the homonuclear /-coulings, which complicated the measurements of T2- Some papers have dealt with suppression of the unwanted... 

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