A

-ia -1. iy - iy ; 2. - ix - - iy ; 3. - iy - iy ;4. ix - - iy sum = iy - iy + iy - iy = 0 +ix -1. ix - ix ; 2. - ia; 3. ix - - ix; 4. ia sum = ix - ix = 0 (ia is not observable in the FID)

-2iyif ^ i. 2iyi? ^ 2iyi?; 2. - 2iyix; 3.2iyi? ^ - 21^; 4.215ix sum = 2iy- 2iy= 0 (—2iyiX and 2i^iX are not observable)

So the filter gets rid of everything except the two terms (one diagonal and one crosspeak) that come from the DQC portion of the second term —2iXiycs'. The results carry along the cs' = cos(^a i1)sin(^ Jt1) term, which makes both peaks antiphase in F1 as well as in F2. Singlet signals (including solvent), which cannot exist as DQC because there is no J coupling, are eliminated altogether. Furthermore, both diagonal peaks and crosspeaks have the same phase in a DQF-COSY spectrum, so that both can be phase corrected to be pure absorption mode.

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