Proton coupled

We often see splitting patterns in which the intensities of the individual peaks do not match those given in Table 13 2 but are distorted in that the signals for coupled protons lean toward each other This leaning is a general phenomenon but is most easily illus trated for the case of two nonequivalent vicinal protons as shown m Figure 13 18... 

FIGURE 13 18 The appear ance of the splitting pattern of two coupled protons de pends on their coupling con stant d and the chemical shift difference Av between them As the ratio Av/d de creases the doublets be come increasingly distorted When the two protons have the same chemical shift no splitting IS observed... 

One kind of 2D NMR is called COSY, which stands for correlated spectroscopy With a COSY spectrum you can determine by inspection which signals correspond to spin coupled protons Identifying coupling relationships is a valuable aid to establishing a molecule s connectivity... 

In the simplest cases the number of peaks into which a signal is split is equal to n + 1 where n is the number of protons to which the proton in question is coupled Protons that have the same chemical shift do not split each other s signal... 

Most of the Moco enzymes catalyze oxygen atom addition or removal from their substrates. Molybdenum usually alternates between oxidation states VI and IV. The Mo(V) state forms as an intermediate as the active site is reconstituted by coupled proton—electron transfer processes (62). The working of the Moco enzymes depends on the 0x0 chemistry of Mo (VI), Mo(V), and Mo (TV). 

Vicinal coupling constants Jhh indicate very clearly the relative configuration of the coupling protons. Their contribution depends, according to the Karplus-Conroy equation... 

For the stable conformers 13a-c of a substituted ethane the vicinal HH coupling constants 3Hz for syn-protons and 15 Hz for anti-protons can be derived from Fig. 2.18. If there is rotation around the C-C single bond, the coupling protons pass through the syn configuration twice and the anti configuration once. 

Vicinal CH coupling constants Hqh resemble vicinal HH coupling constants in the way that they depend on the cosine of the dihedral angle 9 between the CC bond to the coupled C atom and the C//bond to the coupled proton (cf Fig. 2.16), as illustrated by the Newman projections of the conformers 20a-c of a propane fragment. 

The connectivities found in the HH COSY diagram reveal two partial stuctures A and B according to Table 44.1. These are supported by the identical proton-proton coupling constants of the coupling protons. 

---