COSY spectrum of codeine
This is a 2D experiment that shows which Hs are coupled to each other. For simple spectra, this information can often be extracted by measuring and matching couplings, or by selective decoupling, but unless this can be done very quickly, a COSY is more efficient, because all coupling information is obtained in one experiment.
| The sample was 3.3 mg of codeine in .65 ml CDCl3
Interactive view – Those who have installed the Chime plug-in can view and manipulate the codeine structure in 3D, examine and expand the 1H spectrum, and interactively correlate 1H peaks with H atoms in the structure.
One way to view a 2D spectrum is as a 3D, or "stacked", plot. However, it is difficult to measure peak frequencies using this type of plot, and many peaks are obscured behind larger peaks. The more useful representation is a contour plot, in which peaks are represented by a series of concentric rings (contour lines) drawn at vertical intervals, analogous to a topological map. Taller peaks are drawn with more contour lines. The 2 plots below illustrate these 2 view for the same region of the COSY spectrum.
For COSY data (as with all homonuclear 2D plots), the diagonal (indicated by green line in the figure below) consists of intense peaks that match the normal spectrum, as do projections onto each axis.
The coupling information is contained in the off-diagonal peaks, called cross-peaks. The coordinates of each cross-peak are the chemical shifts of the 2 Hs that are coupled. The cross-peak shown in red "connects" protons at 2.7 ppm and 5.7 ppm (H-16 and H-3, referring to the numbering scheme shown above).
The spectrum is symmetrical about the diagonal – a peak located in the upper left triangle will have a corresponding peak in the lower right triangle of the plot.
Coupling "networks" can be traced out, as shown in the figure below.
|The colored arrows trace out coupling networks, corresponding to:
H-3 —> H-5 —> H-10 —> OH
H-3 —> H-16
H-16 —> H-11
Table of COSY correlations
|6.6||6.7||7 – 8|
|5.7||5.3||3 – 5|
|5.7||2.7||3 – 16|
|5.3||4.2||5 – 10|
|5.3||2.7||5 – 16|
|4.9||4.2||9 – 10|
|4.2||2.9||10 – OH|
|3.3||2.4||11 – 14|
|3.3||2.3||11 – 18′|
|3.0||2.4||18 – 14|
|3.0||2.3||18 – 18′|
|2.6||2.4||13 – 13′|
|2.6||2.1||13 – 17|
|2.6||1.9||13 – 17′|
|2.4||2.1||13′ – 17|
|2.4||1.9||13′ – 17′|
|2.1||1.9||17 – 17′|
512 complex points in direct dimension
128 t1 increments
1 sec relaxation delay
Total acquisition time: 5 min
Including setup, processing and plotting, total time was 15-20 min.
sine squared window function was applied in both dimensions (with 0 degree phase shift)
2x zero-fill was used in the indirect dimension, for a final data size of 512 x 512
magnitude calculation (no phasing is required)
For details on processing, see COSY processing
Last updated: 11/27/2006