Homonuclear front end

UNDERSTANDING COSY WITH PRODUCT OPERATORS 9.5.1 Analyzing the Homonuclear Front End ... 

We saw in Chapter 9 that the homonuclear front end 90 -/i-90J gives us four terms for the Ha-Hb system ... 

The DQ filter destroys all terms from the homonuclear front end except for the one with both operators Ia and Ib in the x-y plane the second term — 2IaIb c s. This term will become the diagonal and the crosspeak in the DQF-COSY spectrum. To understand its fate we will express it in terms of pure ZQC and DQC... 

Now we apply the final 90° pulse, but in four consecutive scans we cycle the phase of the pulse as follows x, y, —x, —y. The receiver phase is cycled in the reverse sense jc, —y, —v, y. This is the essence of the DQ filter We will see that only the DQ part of the — 2IaIb term will survive this phase cycle. The other three terms from the homonuclear front end, as well as the ZQC portion of the third term, will be canceled in the phase cycle. Let s write out the result of the phase cycle for the DQ term first... 

Most homonuclear 2D (1H-1H) experiments have the same front end they start with the sequence 90° — t — 90°. Let s follow the net magnetization of a single proton, Ha, with... 

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