Decouplings pictures

Further information is derived from the NOE difference spectra with decoupling of the methyl protons. Table 51.2 summarises the most significant NOE enhancements to complete the picture. 

What one requires is a self-consistent picture of the interface, including both metal and electrolyte, so that, for a given surface charge, one has distributions of all species of metal and electrolyte phases. Unified theories have proved too difficult but, happily, it seems that some decoupling of the two phases is possible, because the details of the metal-electrolyte interaction are not so important. Thus, one can calculate the structure of each part of the interface in the field of the other, so that the distributions of metal species are appropriate to the field of the electrolyte species, and vice versa. 

Stabilized allyl radical will be stabilized further if substituents are introduced. This stabilization occurs to different degrees in the ground state and the transition structure for rotation. In the ground state the substituent acts on a delocalized radical. Its influence on this state should be smaller than in the transition structure, where it acts on a localized radical. In the transition state the double bond and the atom with the unpaired electron are decoupled, i.e. in the simple Hiickel molecular orbital picture, the electron is localized in an orbital perpendicular to the jt(- c bond. 

The Orbital Picture of Resonances from different Decouplings of the Dilated Electron Propagator... 

It is important to note that in this description of spin-coupled nuclei, we begin to see the limitations of the vector approach to understanding the NMR processes involved. In this case it is fairly simple to graft on the quantum aspect of spin orientation to provide an intuitively satisfying picture of decoupling and of the J modulation of spin echoes. Other cases will not be so clear and will force us to adopt a more powerful approach in Chapter 11. 

Attached proton test (APT) can be carried out in several ways, one of which is depicted in Fig. 12.1. It can be readily understood with only the vector picture. The 180° pulse refocuses chemical shifts, but spin coupling evolution occurs only during the period of 1 /J after the first 180° pulse, when the decoupler is turned off. At the end of that period the total signals S are given by... 

This is, of course, a simplified picture since the donor and acceptor stacks are not completely decoupled and a finite charge density wave amplitude on one type of stack induces a small distortion on the other type of stack. 

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