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INADEQUATE

The acronym stands for Insensitive Natural Abundance DoublE QUAntum Transfer Experiment. (Not very informative!)

The experiment maps out the carbon-carbon connectivity via 13C-13C 1-bond coupling.  With only 1% natural abundance, the probability of adjacent carbons being the 13C isotope is 1% of 1%, or 10-4.   

The sample is 200 mg codeine in CDCl3 with Cr(acac)3 to reduce the relaxation time.

Connectivity is established by creating double-quantum (2Q) coherence from a pair of coupled carbons.  The magnetization evolves during t1 with frequency equal to the sum of the offset frequencies of 2 contributing carbons.  The 2Q coherence is then mixed back into both of the 1Q transitions for detection, labeling both peaks in each pair with the same 2Q frequency.  Therefore, a pair of peaks appearing at the same 2Q frequency are coupled.

The 2D spectrum is plotted with the normal 13C spectrum along the horizontal axis and the 2Q frequency along the vertical axis.  

Each C-C connection results in a pair of peaks along a horizontal line.  Pairs of C-C peaks are indicated by the blue lines. (Not all pairs are marked.)

The center of each horizontal connecting line falls along a line, shown below in red, which is f1=2*f2 (where f2 is the normal 13C dimension, and f1 is the 2Q dimension).  

Because of the symmetry, connectivity can be established even if one of a pair of peaks is too weak to be observed.   The signal-to-noise in this spectrum is not sufficient to see peaks from some of the low-intensity quaternary peaks.  Missing are peaks 1-2, 1-4, 1-8, 4-6 and 4-15.

Note there is an artifact peak in the center of the spectrum, in both dimensions.

Part of the aliphatic region is shown below.  The red arrows trace the carbon backbone, starting with C-18 in the upper right corner:   18 –> 11 –> 16 –> 15 –> 17 –> 13. 

 

Acquisition Parameters:

2048 complex points in direct dimension
128 t1 increments
350 scans
1 sec. relaxation delay
Total acquisition time: ~ 13.5 hrs

Processing:

window function was 10 Hz exponential linebroadening in both dimensions
1x zero-fill in the indirect dimension
magnitude calculation (no phasing is required)
final data size 2048×256

See also: detailed description of 2D processing

 


Last updated: 12/23/2002