NMR Samples Types of NMR tubes n Sample

NMR Samples Types of NMR tubes n. Sample preparation n 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. CDCl 3 , C 6 D 6 , acetone-d 6 , 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

Clean clear solution GOOD! NMR Sample Preparation 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 n. Choice of solvent n. Homogeneity of magnetic field n. Data acquisition parameters n. Processing procedures n 5

Good spectrum ppm 6

Good spectrum ppm Peak picking Integrals ppm scale ppm 7

Good spectrum 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 sample requirement Experiment (per 0. 5 ml 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. solution) 2 X 2 hrs 100 + 360 MHz Comprehensive 1 H NMR + Indirect 13 C Observation 100 mg 3 hrs 100 or 360 MHz Pulse Width Calibration and B 1 100 mg 2 X 2 hrs 100 + 360 MHz Rare spin NMR concentrated (80 -90%) 3 hrs 360 MHz Decoupling 1 H from 13 C and B 2 100 mg 2 hrs 100 + 300 MHz Spin Echo and Spin/Spin Relaxation, T 2 100 mg 2 hrs 100 + 300 MHz Spin/Lattice Relaxation, T 1 100 mg 3 hrs 360 MHz Nuclear Overhauser Effect 25 mg 2 hrs 360 MHz Polarization Transfer and DEPT 100 mg 3 hrs 300 MHz 13 C CP/MAS in Solids (sample provided) 21 1 13 2 hrs 360 MHz HETCOR ( H/ C COSY)