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• Four frequencies are detected by the receiver:
A2 = νA (Xα)
A1 = νA (Xβ)
X2 = νX (Aα)
X1 = νX (Aβ)
B) Magnitude Spectrum
• FT with respect to t2 yields four signals at A1, A2, X1, and X2.
These signals are modulated in t1 with these same four frequencies.
• FT with respect to t1 gives a 2D NMR spectrum with four groups of
signals, each containing four signals.
♦ Groups centered at (νA, νA) and (νX, νX) are diagonal peaks.
♦ Groups centered at (νA, νX) and (νX, νA) are cross peaks.
♦ Within each group, separation in F1 and F2 is JAX. -9- C) Phase-Sensitive Spectrum - 10 - 5. Two-Dimensional Homonuclear (H,H)-Correlated NMR
Same as COSY-90, but second 1H pulse is 45˚x' instead of 90˚x'.
Reduces the intensity of the signal, but simplifies the spectrum.
COSY-90 COSY-45 H3 H2 H1 H2 H1 COOH
Cross-section of COSY-45 - 11 - 6. Two-Dimensional Homonuclear (H,H)-Correlated NMR
Spectroscopy. Long-range COSY:
A fixed delay ∆ (0.1 to 0.4 s) is added before and after the second 1H
90˚x' pulse: Allows development of correlation effects for very weakly coupled 1H. h Long-Range COSY COSY-90
CH(2) CH2(4) CH2(3) CH(2) CH2(3) CH2(3) CH2(3) CH2(4) CH2(4) CH2(4) F1
(ppm) CH(2) F1
(ppm) CH(2) F2 (ppm) F2 (ppm) - 12 -...
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This note was uploaded on 11/13/2011 for the course CHEM 4190 taught by Professor Staff during the Fall '08 term at University of Georgia Athens.
- Fall '08