J coupling evolution

Experimental Example 1H Observe with J-Coupling Evolution Only... 

The idea of frequency selectivity is certainly not restricted to J-coupling mediated polarization transfer. Furthermore, frequency selective polarization transfer can also be realized by DQ recoupling techniques. For the technique of shift-evolution-assisted selective homonuclear recoupling (SEASHORE), which employs POST-C7 to construct an effective DQ coupling [82, 83], frequency selective polarization can be achieved when the transmitter offset is set to the... 

A first pulse create.s transverse magnetization components (coherences) which evolve in the evolution period tl (DO in the schemes) with their characteristic precession frequencies (chemical shift and homonuclear J-coupling). The effect of the second (mixing) pulse is that information from one nucleus that evolves in tl is transferred to another (J-coupled) nucleus, the magentization components of which evolve and are detected in t2. Therefore, the nuclei carry information that relates not only to their own chemical shifts and coupling constants but also the corresponding information about the other, coupled spins. 

Let s pick a concrete example we are familiar with the INEPT transfer from ll to 13C. The simplest INEPT sequence is just 90°(1H) — x — 90°(1H)/90°(13C), where the x delay is for /-coupling evolution of the ll doublet into antiphase and the simultaneous 90° pulses give coherence transfer from ll to 13C. Normally, we would set this delay to 1/(2 J) to get complete conversion from in-phase to antiphase ll coherence (I 2IVS-), and we would put... 

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... 

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