15 - COSY 2 - present to all other spins. These reproduce...

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1 COSY vs. DQF-COSY The DQF-COSY does not suffer from the broad dispersive diagonal peaks of the COSY. Peaks close to the diagonal are easier to detect.
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2 Why we do not (and do) collect a COSY: The COSY is more sensitive so if you do not need phase sensitive data, it works well.
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3 The pulse sequence: Spins have gone through a double quantum filter (2 quantum after the second 90, the third converts the signal back to single quantum (which can be observed). Singlets are suppressed (they have no multiple quantum coherence).
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4 More about coupling in phase sensitive COSY experiments: The A 3 X in the COSY map This is an anti phase quartet
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5 More multiplet “structures”
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6 Passive and active coupling Active coupling: is the coupling that gives rise to the crosspeak (the A and X crosspeak, e.g., will show the basic antiphase splitting in both dimensions and thus, produces the basic antiphase square array from which all COSY crosspeaks are ultimately derived. Passive coupling are those
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Unformatted text preview: present to all other spins. These reproduce the antiphase array without introducing any further changes in sign. 7 Look at the middle MX crosspeak. The small J mx coupling (6 Hz) shows the change in sign; it get repeated by the large AM coupling (18 Hz) 8 Active and passive in action The active coulping shows the sign change (6 and 8 Hz) and the large passive coupling does not. Note that you now resolve the F from the Y in 2 dimensions. N C O H H OH 9 A region of the DQF-COSY spectrum of the molecule shown above (an andrographolide). Methylenes are H A -H B and H C-H D . We would know these from CH correlation data. Note weak and strong coupling constants for this part of the molecule. (H E-H C are strong, e.g.) 10 A real problem: 11 1 H spectrum with expansion: 13 C spectra: 1 H-decoupled and off-resonance decoupled (shown above the segmented fully decoupled experiment) 12 A 1 H-13 C correlation map...
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15 - COSY 2 - present to all other spins. These reproduce...

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