NMR of Nuclei other than 1H/13C How do you decide if a nucleus is reasonable to detect? Check the NMR Active Nuclei Table. 1) Gyromagnetic Ratio and Natural Abundance: Larger  = higher field = higher sensitivity Greater natural abundance = higher sensitivity 2) Spin- Spin 1/2 is ideal Spin > 1/2 leads to faster relaxation and thus broader lines

NMR of Nuclei other than 1H/13C Other Important Information 1) Chemical Shift Range (in ppm)- the total normal range of chemical shifts, for example 1H = 13 ppm in the table 2) Chemical shifts of various groups. For example this is the entry for 19F: Moiety Chemical shift (ppm) Fluorides -300 to 200 3) Some sort of a reference compound and reference shift (sometimes more than one compound and not necessarily 0 ppm). F19: CFCl3 = 0 P31: Phosphoric Acid N15: CH3NO2 = 0 (IUPAC), but liquid NH3 = 0 for instruments* [380.5 ppm difference]

NMR of Nuclei other than 1H/13C Other Important Information 4) Pulse sequence to use: Basic or Inverse gated Is the NOE negative or positive? Any nucleus with a negative gyromagnetic ratio (15N, 29Si, 113Cd) has negative NOE for a small molecule. 5) T1 time Long T1 time = low repetition rate (scans/minute) 6) Line Width Sharper line, more intense line, as the integration of the peak is conserved, not the intensity.

How do you acquire a 1D on nuclei other than 1H or 13C on our spectrometers? 1) Nucleus must be within the frequency range that the probes on our spectrometers can detect. Consoles can only pulse at specific frequencies. The 500 can pulse at 500 MHz only on channel 2, any frequency from 0 to 500 on channel 1, and any frequency from 0 to 300 Mhz on channel 3. (the 600 is similar- replacing 500 with 600).

How do you acquire a 1D on nuclei other than 1H or 13C on our spectrometers? 2) Probe must be tuned to appropriate nucleus. The 600 probe is fixed at 600/150/60. The normal 500 probe can tune 450-550 on the high frequency coil and 50-220 on the low frequency coil with appropriate inductor/capacitor sticks except we do not have the appropriate stick for ~130-180 MHz and ~60-70 MHz. The normal 300 probe can tune from ~270-330 on high frequency and 27-150 with appropriate stick on low frequency channel The 400s are tuned to 400/380 on the high frequency channel and 160/100 on the low frequency.

How do you acquire a 1D on nuclei other than 1H or 13C on our spectrometers? 3) Normal 1D parameters must be set- pw, tpwr, d1, at, sw, tof, etc. However, you will likely have no idea what the appropriate parameters are ahead of time They must be calibrated (or estimated based upon literature values) Pulse widths can be measured in the same way as with 1H pulse widths Use T1 estimate from table to guess at what d1 should be. T1 can be measured in the same way as for 1H. Correct measurement can provide information on how long to set d1 and pulse width. Acquisition time is set in the same way as for 1H data. The resolution is determined by the acquisition time, but the amount of real data (or the natural line width) is correlated to relaxation (T2).

How do you acquire a 1D on nuclei other than 1H or 13C on our spectrometers? 4) Scalar Coupling: 1H decoupling can be used as necessary in X nuclei detect experiments. Appropriate decoupling parameters can be copied/measured. As 13C 1D experiments are accomplished with 1H decoupling, copy: dof, dm, dmm, dpwr, and dmf [note dm = ‘nny’ for negative g nuclei]

19 Fluorine 19Fluorine is a sensitive nucleus (475 MHz on a 500 MHz for 1H spectrometer) with sharp signals (spin = 1/2) (except for scalar coupling and has a wide chemical shift range (~700 ppm). A 19F NMR spectrum is very similar to that of proton except for larger coupling constants. Integration of 19F? – Difficult not impossible- T1, off-resonance effects, baseline roll Background signals from the probe cause broad hump in baseline over 100s of ppm. If this is folded into the spectrum, then baseline rolls. Also, the large chemical shift range causes rolling baselines due to the inability of the receiver to turn on fast enough, as well as off-resonance effects. Proton decoupling is of 19F spectra is difficult for spectrometers; it requires at the minimum a probe tuned to both 19F and 1H, since both are high field nuclei, and a console that can pulse at 2 different high frequencies at the same time. (can be done on New400)

19 Fluorine

19 Fluorine 2D 19F spectra are also possible. 19F COSY or TOCSY should be essentially the same to acquire as a 1H COSY or TOCSY. Similar the 19F/13C HSQC or HMBC or HMQC. As long as the 19F pulse width is calibrated and the spectral width for fluorine is sufficient but not so large to significantly decrease resolution in the 19F dimension. A 19F/1H COSY or HMBC etc., however is difficult, requiring two high frequency channels as with 1H decoupling of 19F. Through-space connections can be made by NOESY for 19F/19F interactions, or 19F ROESY. The HOESY (Heteronuclear Overhauser Effect SpectrocopY) is a heteronuclear version of NOESY for 1H/19F NOEs but like the 1H/19F COSY is difficult to accomplish.

Hardware Setup for 19F/1H

F19/1h decoupling, f19/c13 hmqc/hmbc, F19-1H HOESY

31 Phosphorus The 1D 31P NMR experiment is much less sensitive than 1H but more sensitive than 13C (202 MHz on a 500 MHz for 1H instrument). 31P yields sharp lines (spin = 1/2) and has a wide chemical shift range (~350 ppm) It is usually acquired with 1H decoupling means that spin-spin couplings are seldom observed, but 1H decoupling could be turned off to measure 1H/31P coupling constants. 31P NMR spectrum has uneven NOE enhancement of the signals by decoupling Long longitudinal relaxation times. Large coupling constants- 1JHP ~180-700 Hz Couplings may be observed with other nuclei such as 19F, also large coupling constants A 31P/1H heteronuclear COSY is good for measuring 31P/1H coupling constants.

31 Phosphorus 31P relaxes by both dipolar means (contributing to NOE) and by CSA (Chemical Shift Anisotropy). The effect of CSA on T2 relaxation is significant and increase as a square of the applied field, so T2 gets shorter at higher field (broader 31P lines at high field). Since resolution increases linearly with the field at some point (this would be sample dependent), the resolution is worse as the field is increased.

1H/31P COSY

Deuterium 2H NMR is usually used for field frequency lock. At natural abundance it has very low sensitivity but when enriched it is of medium sensitivity (76 MHz on a 500 MHz for 1H instrument). Deuterium usually yields broad signals whose line width typically varies between a few hertz and a few kilohertz (spin = 1, quadrupolar moment = 2.73 x 10-31). Although broad, the lines for deuterium are not as broad as most quadrupolar nuclei as the quadrupolar moment is smaller than most quadrupolar nuclei (for example 17O = -2.6 x 10-30 or 97Mo = 1.1 x 10-28). The spectrum has the same narrow chemical shift range as for 1H but lower resolution and lower sensitivity.

Deuterium The main uses of deuterium spectra are Determining the effectiveness of chemical deuteriation Studying isotope effect Relaxation studies (since deuterium relaxation is faster than 1H, then you can change the time regime that you can study) Gradient shimming.

Deuterium Deuteration of a sample can: Simplify 1H spectra, by removing 1H resonances that you do not care about Sharpen 1H lines, as there less protons for 1H /1H dipole-dipole relaxation (the efficiency of dipole-dipole relaxation depends upon the gyromagnetic ratio). Thus, large proteins are often deuterated on side chain resonances to sharpen lines and remove complexity from spectra.

Deuterium spectrum

Nitrogen Nitrogen has two NMR active nuclei. 15N yields sharp lines (spin = 1/2, <1 Hz line width) but is very insensitive (50 MHz on a 500 MHz for 1H instrument, 0.4% natural abundance). 14N is a medium sensitivity nucleus (35 MHz on a 500 MHz for 1H instrument, 99% natural abundance) but its signals are usually significantly broadened (spin = 1, ~ >15 Hz line widths) by quadrupolar interactions sometimes to the extent that they are unobservable on a high resolution NMR spectrometers. 14N linewidth correlated to quadrupole moment. The nitrogen chemical shift range is wide (900 ppm) and so may be readily used for distinguishing nitrogen species. In 2D, 15N is a little worse than 13C (especially in natural abundance), but with 15N labeling in 2D is somewhat better at very high field (sharper lines, especially at high field).

11 Boron 11B NMR is moderately high sensitivity nucleus (160 MHz on a 500 MHz for 1H instrument, 80% natural abundance) which yields moderately broad lines (spin = 3/2, ~20Hz line width). It has a moderate chemical shift range (~200 ppm), which is normally sufficient to identify how many boron exist in the sample The spectrum always contains a background signal from the glass in the tube and probe.

11Boron Spectra

29 Silicon 29Si NMR is a low sensitivity nucleus (100 MHz on a 500 MHz for 1H instrument, 4.7% natural abundance) which yields sharp lines (spin = 1/2, < 1Hz line width). It has a wide chemical shift range (~600 ppm) so it is good for determining the chemical environment in silicon compounds. The spectrum always contains a background signal from the glass in the tube and probe at -110 ppm. If there is not enough sensitivity to observe a spectrum, use the projection of a heteronuclear correlation with an HSQC/HMQC/HMBC, or DEPT. Chemical shift (ppm) Hexacoord. Silicon -190 to -125 Silanes -125 to 20 Silicates -120 to -70 Silicon halide -346 to -40 Transition metal silyl -90 to 1

51 Vanadium 51Vanadium is a sensitive nucleus which yields broad lines and has a very wide chemical shift range. It can be used to examine the chemical and oxidation state of vanadium. However, the V(II) and V(IV) are paramagnetic; their presence in solution makes the detection of a high-resolution 51V spectrum impossible. Spin = 7/2 Natural Abundance = 99.76% Frequency = 0.26*1H Frequency; = 131 MHz on 500 MHz T1 ~0.02 s Linewidth ~ 21 Hz Chemical Shift (ppm) V(-I) -1900 to -1650 V(I) -1600 to -1000 V(V) -800 to -400 VOCl3 0

17 Oxygen and other Fast Relaxing Quadrupolar Nuclei 17O is an insensitive nucleus (65 MHz on a 500 MHz for 1H instrument) and has a very low natural abundance (0.04%). The nucleus yields very broad signals (spin = 5/2; line width = 70 Hz, T1 = 0.02s). The chemical shift range is very wide (1200 ppm) but 17O remains a difficult nucleus to observe. Spectra of 17O and other quadrupolar nuclei with short T1 times (broad lines) can be improved with special pulse sequences or proper setting of acquisition parameters. True 90º pulses are always used since T1 is so short, very short relaxation delays and acquisition times are used enabling rapid pulsing, high repetition rate (scans per minute).

17 Oxygen and other Fast Relaxing Quadrupolar Nuclei Acoustic ringing after a pulse in the probe causes broader lines, particularly low-frequency nuclei. Special acquisition parameters, mostly short times before acquisition are used to account for the rapid relaxation of the nuclei (on a Varian there are delays called alpha and rof2). By shortening this delay, significant phase errors are incorporated into the spectrum Processing techniques are used to replace the first few data points which are not correct because the relaxation is fast relative to the time the digitizer can turn on and begin acquiring real data.

17 Oxygen and other Fast Relaxing Quadrupolar Nuclei ACOUSTIC (Alternate Compound One-eighties USed to Suppress Transients In the Coil) uses two acquisition times, where the acoustic ringing ideally cancels itself out as the phase of the receiver is inverted after 180º then 90º pulses, but the real data adds.

17O NMR of Ethyl Acetate C) Same Data as in B but with Application of Backwards Linear Prediction B) Standard 1D Pulse Sequence ACOUSTIC Ringing Suppression Pulse Sequence

17O Spectra of D-mannopyranose No Solvent Suppression; 2 observed resonances are H2O and DMSO. Solvent Suppressed Spectra. ~2.5 hours of acquisition on 0.25M D-mannopyranose sample. Acquisition time = 8 ms; relaxation delay = 1 ms. 106 scans.