Transcript Document
NMR Samples Types of NMR tubes Sample preparation 1 Types of NMR Tubes Solid State Sample Rotors Solution NMR Sample Tube Spinners NMR Sample Tubes with Caps 2 NMR Sample Preparation 5 mm • Use clean + dry NMR tubes and caps (tubes can be re-used, caps should not!) • 0.5 ml deuterated solvent (i.e. CDCl3 ,C6 D6 , acetone-d6 ,etc.) • substrate requirements for routine spectra: 10 mg for proton NMR 100 mg for carbon-13 NMR • min. filling height of tube: 2 inches (5 cm) • Cleaning of tubes: 1. rinse with solvent you were using 2. rinse with acetone 3. dry in (vacuum-)oven at low temperature 3 NMR Sample Preparation Clean clear solution GOOD! Suspension or opaque solution Precipitate Not enough solvent Two phases Bad Samples! Concentration gradient 4 Good and bad NMR Spectra … are the result of: Sample preparation Choice of solvent Homogeneity of magnetic field Data acquisition parameters Processing procedures 5 Good spectrum ppm ppm 6 Good spectrum ppm Peak picking Integrals ppm scale ppm 7 Good spectrum ppm ppm 8 Bad spectrum ? 9 Bad spectrum ! No units specified for axis and peak picking Signal/Noise ratio bad 10 Bad spectrum ? 11 Bad spectrum ! Tall signals are cut off 12 Bad spectrum ? 13 Bad spectrum ! Signals too small (only allowed to compare signal intensities between different spectra) 14 Bad spectrum ? 15 Bad spectrum ! Broad signals (bad sample, poor shimming, wrong processing parameters) 16 Bad spectrum ? 17 Bad spectrum ! Signals are distorted Excessive peak picking (automatic phase correction is often insufficient) (low p.p. threshold, also due to improper phasing) 18 Bad spectrum ? 19 Bad spectrum ? Areas without signals should be excluded. (If you want to print all your spectra with a default range, i.e. 0-10 ppm, don’t forget to print detailed expansions.) 20 Lab Assignments Duration Spectrometer 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 2X2 hrs 3 hrs 2X2 hrs 3 hrs 2 hrs 2 hrs 3 hrs 2 hrs 3 hrs 2 hrs 100 + 360 MHz 100 or 360 MHz 100 + 360 MHz 360 MHz 100 + 300 MHz 100 + 300 MHz 360 MHz 360 MHz 300 MHz 360 MHz 11. 2 hrs 360 MHz Experiment sample requirement (per 0.5 ml solution) Comprehensive 1H NMR + Indirect 13C Observation 100 mg Pulse Width Calibration and B1 100 mg Rare spin NMR concentrated (80-90%) Decoupling 1H from 13C and B2 100 mg Spin Echo and Spin/Spin Relaxation, T2 100 mg Spin/Lattice Relaxation, T1 100 mg Nuclear Overhauser Effect 25 mg Polarization Transfer and DEPT 100 mg 13C CP/MAS in Solids (sample provided) HETCOR (1H/13C COSY) 100 mg 1H COSY / NOESY (optional) 25 mg Use your own samples, if possible. Familiarize yourselves with the procedures for each experiment, before you come to the lab. Print the manuals. 21