NMR service details

General Introduction

The department has five Bruker NMR spectrometers and extensive off-line NMR data processing facilities. The purpose of these notes is to give an out line of the type of NMR hardware the department possesses and what types of experiments may be routinely performed using this equipment.

 Bruker DRX 500 magnet

NMR Spectrometers

Bruker Avance 400 (DPX-400)

This spectrometer has a standard geometry 5mm 1H/13C/19F/31P probe. It can perform a wide variety of 1D and 2D experiments. With its sample changer and Icon-nmr, this machine is now used predominantly for undergraduate teaching.

Bruker Avance 400

This spectrometer has a standard geometry 5mm 1H/13C probe and is equipped with sample changer. It is open access using Icon-nmr. This spectrometer is used by the level 4 undergraduates and the majority of postgraduates in the Department.

Bruker Avance III HD 400

This spectrometer has a standard geometry 5mm BBFO probe with a single z-gradient and can observe 1H,13C,19F,31P and most NMR active isotopes in the periodic table. Experiments such as HH-COSY, JMOD, DEPTQ can be performed routinely. It is open access with sample changer and Icon-nmr. The vast majority of the routine Level 4 and postgraduate NMR samples are run on this spectrometer.

Bruker Avance III 400

This spectrometer has a standard geometry 5mm BBFO probe with a single z-gradient and can observe 1H,13C,19F,31P and most NMR active isotopes in the periodic table. The probe has been constructed to give maximum sensitivity to X-nuclei not 1H. It can perform a wide variety of 1D and 2D experiments and has variable temperature capabilities of ca. ± 100 °C.

Bruker Avance III HD 500

This spectrometer has three probes: a standard geometry 5mm BBFO probe, an inverse geometry 5mm VSP probe, and a 4mm CP/MAS probe. Both solution probes have a single z-gradient and can observe 1H and most NMR active isotopes in the periodic table. It can perform a wide variety of 1D and 2D experiments and has variable temperature capabilities of ca. ± 100 °C. The CP/MAS probe can observe 1H/19F on 1H channel and 14N-31P on BB channel. 4mm rotors, with a maximum spinning speed of 15 kHz, of different sample sizes (12uL, 50uL, and 80uL) are available.

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NMR experiments

There are many types of NMR experiment, the time and amount of compound required varies enormously. A simple 1H spectrum can be completed in minutes whereas a ROESY experiment on a weak sample may take all weekend. The following is just a very small selection.

1H experiments
  • Routine 12 ppm sweep width with integration – sweep width may have to be adjusted to take into account acid protons etc.
  • Samples run in D2O will normally be run with pre-saturation of the large residual HOD signal and consequently signals from exchangeable protons such as NH’s will be missing.
  • Coupling between protons can normally be established using a simple 2D COSY experiment. Using gradients a COSY experiment can be performed in a few minutes.
  • Inverse CH correlation tying the 1H and 13C spectra together – it is often easier to assign the 13C spectrum and this techniques enables the 1H signals to be assigned.
13C experiments
  • Routine 250 ppm sweep width using JMODulation or DEPTQ. These experiments sort the carbons into even (CH0 and CH2) and odds (CH1 and CH3). Check the solvent signal, it will always be even.
  • Spectra with broad signals may be run using standard composite 1H decoupling.
  • 13C spectra are never integrated.
19F experiments
  • Routine 300 ppm sweep width with and without 1H decoupling. 19F are usually measured on the Avance III HD 400.
31P experiments
  • Routine 150 ppm sweep width with and without 1H decoupling. Other sweep widths and range available.
Remember

Whilst the sample may be confidential it very important that all relevant information is noted on the NMR form such as 1H signal expected at 13 ppm or 13C signal at –35 ppm. Similarly it is important that the sample dissolves fully in the NMR solvent otherwise the spectrum relates not to the compound but to the compound and the soluble impurities.

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Sample quantities

Sample quantity depends upon the nucleus and experiment required:

  • 1H and 19F typically between 10 to 20 mgs.
  • 13C roughly in the region of 5 mgs per carbon atom.
  • 31P typically between 30 to 50 mgs.

These figures are only "ball-park" figures and it depends on molecular weight, symmetry, sample availability and solubility.

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NMR solvents

A wide range of deuterated NMR solvents is available. The cost of deuterated solvents varies enormously from a few pence a ml for chloroform-d to over £10 a ml for N,N-dimethylformamide-d7. Depending on the choice of solvent there may be a surcharge as shown in the table below:

Solvent Costs Included
Solvent Surcharge

Acetonitrile-d3
Acetone-d6
Benzene-d6
Chloroform-d
Deuterium oxide
DMSO-d6
Methanol-d4
Nitromethane-d3
Pyridine-d5
Toluene-d8

Dichloromethane-d2
N,N-Dimethylformamide-d7
Tetrahydrofuran-d8

If required, other solvents may be purchased.

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Version 20150409.1