Signal splitting

The —OH proton of a primary alcohol RCH2OH is vicinal to two protons and its sig nal would be expected to be split into a triplet Under certain conditions signal splitting of alcohol protons is observed but usually it is not Figure 13 21 presents the NMR spec trum of benzyl alcohol showing the methylene and hydroxyl protons as singlets at 8 4 7 and 2 5 respectively (The aromatic protons also appear as a singlet but that is because they all accidentally have the same chemical shift and so cannot split each other)... 

It is by no means unusual to come across compounds which contain more than one phosphorus atom Fig. 23 shows the proton decoupled coupled phosphorus spectrum of compound 6, which contains three chemically different phosphorus nuclei. Phosphorus behaves in NMR just like the proton, so we shall expect to see three signals, split into multiplets if there is an observable coupling between the phosphorus nuclei. 

Fluorine usually makes its presence felt in a fairly spectacular fashion, when it is present in a molecule. Once again, I = 1/2, so we only have two allowed states to worry about. Unlike 13C however, fluorine has only one isotope, 19F, and as this of course, has 100 % natural abundance, we see the whole proton signal split, instead of a couple of tiny satellites on either side of our signals ... 

Dipolar coupling (vectorial coupling) only occurs between spatially close nuclei and acts through space. Generally, however, signal splitting does not occur in solution because... 

Coupling constant magnitudes (mostly reported without sign) may be read from signal splittings. This, however, is possible only if the spectrum (or subspectrum) is first order, i.e., if the ratio R of the chemical shift difference of the coupling partners X and Y (dv in Hz) and... 

Resolution enhancement on the other hand is applied to resolve overcrowded spectral regions or to measure very small signal splitting caused by J-coupling. 

Signal splitting, as observed in the case of hydrogen fluoride, is a phenomenon often encountered in organic molecules with adjacent hydrogens. 

The arrangement of trans isoprene-units is observed more in detail from the 13C-NMR signal splitting of C-l methylene carbon [94, 97], as shown in Figure 11.19. The mushroom rubber shows two peaks due to the trans isoprene-unit in dimethylallyl-trans and trans-trans linkages similar to those of the two-trans polyprenol. On the other hand, the rubbers from Goldenrod and Sunflower exhibit three peaks similar to the overlap of peaks of two-trans and three-trans polyprenols. This suggests the presence... 

Isotope effects on coupling constants are more difficult to recognize than isotope effects on chemical shielding. The difference of chemical shifts between isotopomers is easier to determine than slightly differences in signals splitting. The primary isotope effect on coupling constant defined as ... 

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