MICHIGAN STATE UNIVERSITY
gHMQC/gHMBC
Department of Chemistry

(A PDF version of this page is available from the Handouts site)

MTR Resources
Heteronuclear Multiple Quantum Coherence (HMQC) and Heteronuclear Multiple Bond Coherence (HMBC) are 2-dimensional inverse H,C correlation techniques that allow for the determination of carbon (or other heteroatom) to hydrogen connectivity. HMQC is selective for direct C-H coupling and HMBC will give longer range couplings (2-4 bond coupling). Our facility implements gradient-selected versions of both HMQC (gHMQC) and HMBC (gHMBC), which improves the acquired spectra by significantly reducing unwanted signal artifacts.
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Determine 1H-13C connectivity (HMQC, HMBC)

 
NOTE: The above 1D spectra can be obtained earlier and retrieved for the HMQC experiment, but we recommend, at the very least, you should acquire the proton spectrum before every gHMQC run.

 

Data Manipulation:
Interacting with the 2-D Color Map/Contour Map
To do the following...
You should...
Increase/Decrease the scale
Click on either vs+20% or vs-20% or type vs2d=vs2d*1.5 and click Redraw. The typed command increases the display by a factor of 1.5. You can use a larger number if you like (e.g. vs2d=vs2d*2, increases by a factor of 2.
Change the number of color levels
Use the middle mouse button to click on the color scale to the right of the color plot. Click on the smaller number to increase the number of colors displayed.
To expand on a region
Ensure that you are in the interactive mode; if not, click Main Menu=>Display=>Color Map. Click with the left mouse button on the left-most point of your desired region. Click with the right mouse button on the right-most point. Click on Expand.
To expand an exact region
Type sp=#p wp=#p (for the F2 dimension, usually vertical) and sp1=#p wp1=#p (for the F1 dimension, usually horizontal), where # are the numbers in ppm for the region of interest. sp designates the start of plot and wp is the width of the plot. You will need to click on Redraw to update the screen. For example, I want to expand the region between 1 and 4 ppm in F1 and between 2 and 4 ppm in F2, I would type sp=2p wp=2p sp1=1p wp1=3p, then I click Redraw to see the result.
To reference the 2-D spectrum
Expand the region of interest. Click Hproj(max) for the horizontal projection and Vproj(max) for the vertical projection. Place the cross-hair cursor on the diagonal position you wish to reference (the projections will help you to orient the cross-hair). Type rl(#p) rl1(#p*dfrq/sfrq), where # is the value in ppm you want to be the reference. rl sets the F2 dimension reference and rl1 sets the F1 dimension reference.
Redisplay the spectrum
Click on Redraw.
Display a projection of the 1D spectrum on the side of the 2-D plot
Click Proj, then click Hproj(max) for the horizontal projection or Vproj(max) for the vertical projection. Use the middle mouse to adjust the scale.
Display a trace of the 2-D plot
Click Trace and use the left mouse button to drag the cursor.
View the contour plot
Click Main Menu=>Display=>Contour
Increase number of levels on contour plot: Interactive plot
Type, for example, dconi('dpcon',15,1.2). The dpcon flag is for displaying the contours. The first number (15, in this case) is the number of contour lines (default is 4). The second number (1.2, in this case) is the relative spacing intensity (default is 2). You can input different numbers if you wish, but the second number must be greater than 1.
Increase number of levels on contour plot: Non-interactive plot
Type, for example, dpcon(15,1.2). The dpcon flag is for displaying the contours. The first number (15, in this case) is the number of contour lines (default is 4). The second number (1.2, in this case) is the relative spacing intensity (default is 2). You can input different numbers if you wish, but the second number must be greater than 1.

 

The processed spectrum should look similar to the one pictured below:

pic of gHMQC spectrum

If, on the other hand, your spectrum looks like this one, then 2-D phasing is necessary:

pic of poorly phased gHMQC

The spectrum above has a phasing issue in the F1 or indirect dimension. Since the description of the phasing approach is rather lengthy, I leave it to the user to go through the detailed method for phasing 2-D spectra, which is available in PDF format from here. It is not that difficult, but it does require a little caution so as to avoid creating a roll in the baseline.

Autoprinting your gHMQC with Projections generated from HMQC (Easy to do, but NOT RECOMMENDED):

Printing your gHMQC with 1-D Spectrum as Projections: Open your gHMQC Spectrum. Click Main Menu=>Display=>Size=>Center. Join another experiment and retrieve the 1-D spectra: Type jexp2 or join the experiment number where your gHMQC resides: Running a Gradient Selected HMBC: Determine Long-range Carbon to Hydrogen Connectivity.

The gHMBC is used to help establish the carbon skeleton through the multiple bond carbon to hydrogen connectivity. This experiment is relatively insensitive as compared to gHMQC because multiple bond correlations are less efficient than one bond correlations. Typical one-bond coupling constants are around 150 Hz whereas multiple-bond coupling constants fall in the range of 5-15 Hz, which is similar to the range for H,H-homocoupling.

*Some sections of this page were adapted from procedures by Long Lee and Kermit Johnson.


Last Updated:  February 14, 2012  - WebMaster
URL: http://www2.chemistry.msu.edu/facilities/nmr/HMQC.html

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