NMR. Obtaining a 13 C NMR Spectrum 1 H Broadband decoupling –Gives singlet 13 C peaks, provided no F, P, or D present in the molecule) –Continuous sequence.

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Presentation transcript:

NMR

Obtaining a 13 C NMR Spectrum 1 H Broadband decoupling –Gives singlet 13 C peaks, provided no F, P, or D present in the molecule) –Continuous sequence of pulses at the 1 H frequency causes a rapid reversal of spin orientation relative to the B 0, causing coupling to 13 C to disappear

1 H channel 13 C channel Broadband Decoupling

H 3 C 4 -C 3 H=C 2 H-C 1 OOH C-1 C-3 C-2 solvent C-4

13 C Chemical Shifts Reference is TMS, sets 0 ppm A range of 200 ppm Chemical shifts can be predicted –Empirical correlations –Ex. Alkanes  i = n  + 9.4n  – 2.5n  + 0.3n  + 0.1n  + Sij 2-methylbutane  i = * *2 – 2.5* = 22.0 (22.3)

Signal averaging 13 C experiment generally take longer than 1 H experiments because many more FIDs need to be acquired and averaged to obtain adequate sensitivity. NOE effect (enhancement/reduction in signal as a result of decoupling) 1H1H 1H1H 13 C N1N1 N4N4 N3N3 N2N2 N2N2 N1N1 N3N3 N4N4 1H1H 1H1H W2W2 W1W1

NOE effect W 2 (Enhancement) dominates in small molecules Relevant for all decoupling experiments

Other more complex 1D Experiments 1 H NOE experiment Inversion Recovery Experiment; Determination of T 1 J modulated Spin Echo INEPT Experiment DEPT Experiment

Targeted 1 H Spin Decoupling Continuous irradiation at a frequency ( 2 ) that corresponds to a specific proton in the molecule during the 1 H NMR experiment All coupling associated with the protons corresponding to 2 disappears from the spectrum

  channel 1 H channel 1 H targeted decoupling (NOE)

TMS

Inversion Recovery