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Unformatted text preview: H
FT 13 X1 X2 90x t H 90x
13 X2 C 90x
1 X1 FT, t=0 90x C What if t 0? 4 HETCOR or C, H-COSY: correlates 1H and 13C chemical shifts
-in this case t1 varies (increasing t1 allows for 1H chemical shift
-we will not ignore chemical shift evolution: MHC
-the vectors MHC and MHC precess and diverge according to 5 H , JCH and t1 H Let’s look at a simple case: assume that during t1, MHC rotates 360° (so that
it ends up on y) and MHC rotates 180° (so that it ends up on –y)
z M HC z 90°x M HC
y y t1 M HC z M HC
y M HC
x x z 90°x M HC
y x M HC x !! This is exactly what we get if we
selectively excite the A2 transition !!
-so, depending on JCH, H, and t1, we can
selectively alter the N1 and N3
populations and alter the signal intensity -When t1 0, the population differences between levels 1 and 3 (the 1HC
transitions) change, and those between levels 2 and 4 (the 1HC transitions)
change, leading to changes in the differences between levels 1 and 2 and
between levels 3 and 4 (the 13C transitions).
-Thus, as t1 is varied, the intensity of the 13C sig...
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- Fall '08