IU NMR user guide

HMBC – Heteronuclear Multiple Bond Correlation Experiment

(Frank Gao, 8/1/01)

The HMBC experiment allows you to correlate carbons (or other X nuclei) and protons linked over more than one bond.

Note: 1) On I500, you have to recable the spectrometer when you change the detected nucleus between proton and ¹³C (or other X nuclei). The other spectrometers do not require hardware changes. 2) The gradient version of HMQC/HMBC experiments is preferred if the spectrometer is equipped with a gradient accessory (e.g., I500). 3) The HMQC/HMBC experiments are best-done using the inverse probe.

1. Setting up the spectrometer

See “IU NMR user guide: HMQC”.

See “IU NMR user guide: HMQC”.

3. Calibrating the ¹H pulse width (optional)

See “IU NMR user guide: HMQC” or “IU NMR user guide: 90º Pulse Calibration – determining the ¹H 180º pulse width of the transmitter”.

4. Setting up and starting a HMBC experiment

1. If on I500, make sure the spectrometer is cabled for ¹H detection
2. Type jexp3                – join the experiment for HMBC
3. Type iuhmbc             – read in the default parameter set for HMBC
4. Enter temp=25 spin=0 su
5. Make sure that the spinning is turned off
6. Enter dof=…             tof from ¹³C spectrum determined in “2. Choosing the spectral windows”
7. Enter sw1=…            sw from ¹³C spectrum determined in “2. Choosing the spectral windows”
8. Make sure that the following parameters are set to their up-to-date values listed at the console:
• pw                     – ¹H 90º pulse width
• tpwr                  – ¹H pulse power
• pwx                   – ¹³C 90º pulse width
• pwxlvl               – ¹³C pulse power
9. The following parameters may be changed upon your sample:
• j1xh                  – average ¹J_CH coupling constant (default 145 Hz)
• jnxh                  – average ⁿJ_CH (n>1) coupling constant (default 9 Hz)
• nt                      – number of scans per FID, must be a multiple of 8
• ni                      – number of data points on the ¹³C dimension
• d1                     – relaxation delay (default 1.5 s)
10. If presaturation is desired, you can set it up in the following manner:
1. Enter phase=1 nt=1 ni=1 ss=0
2. Type ga                     – acquire a spectrum
3. Type mf(4)                – copy the data in the current exp (exp3) to exp4
4. Type jexp4                – join exp4
5. Type wft
6. Set the cursor to the peak that is to be removed by presatuation
7. Type nl movetof
8. Write down the value of tof. It will be the satfrq in the HMBC experiment
9. Type jexp3                – go back to exp3 (for HMBC)
10. Enter satfrq=…         the tof value you determined in the step 8
11. Enter satmode=’y’
12. Enter satdly=1.5       a significant time compared with T₁ of the peak to be presaturated
13. Enter d1=0.05
14. Enter satpwr=10,7,4,1
15. Type ga                     – acquire a series of spectra with different saturated power levels
16. Type wft dssh
17. Find the minimum satpwr for which the peak will be removed, and set satpwr to this value
18. Finally, reset the following parameters for the HMBC experiment:
• phase=1,2
• ss=32             – number of steady-state scans
• nt=16             – number of scans per FID, must be a multiple of 8
• ni=192           – number of data points on the ¹³C dimension
11. Type time       – estimate the experiment time (change nt, and ni to suite your time, nt will cost you S/N, ni resolution in the ¹³C dimension)
12. Type au          – start the HMBC experiment

5. Processing a HMBC spectrum

5.1 During the data acquisition (at least 4 FIDs have been acquired)

1. Type sine(0, xx, ’f1’)     – set up a sinebell weighting function for the ¹³C dimension. xx is the number of FIDs that have been acquired, which can be found in the Acquisition Window, e.g., sine(0, 64, ’f1’)
2. Type wft2da                   – perform a 2D Fourier Transform

5.2 After the data acquisition is completed

• Type iuhmbcproc           – automatically process and display a 2D HMBC spectrum (recommended).
• Alternatively, do it step by step:
1. Enter sinebell       – set the weighting functions for both ¹H and ¹³C dimensions
2. Type wft2da

6. Display a 2D HMBC spectrum

See “IU NMR user guide: HMQC”.

7. Plotting a HMBC spectrum

1. Type full to adjust the position and size of a 2D spectrum to fill the entire screen (and page).
2. Type dpcon(10, 1.5) to see how your 2D spectrum looks if plotted with 10 contours spaced 1.5 level apart. Try other numbers if you wish.
3. The macro command iuplhxcor can be used for plotting a 2D HMBC spectrum (see the manual for this macro by typing man(’iuplhxcor’)), for instance
• iuplhxcor(10, 1.5, 0, 0) to plot the 2D spectrum solely with 10 contours spaced 1.5 level apart;
• iuplhxcor(10, 1.5, 1, 2) to plot the 2D spectrum with 1D ¹H (in exp1) and ¹³C (in exp2) spectra along the respective axes, those 1D spectra should be put in the respective experiments previously;
4. Type pltext to plot the experimental text file.
5. Type iupage (or click page) to send the plot to the printer.