NMR Spectroscopy II Flashcards
1
Q
Carbon 13
A
- Determine magnetic environment carbon atoms instead of protons
- Most of carbon 12 has no spin whereas carbon 13 does have magnetic spin
2
Q
Fourier Transform NMR Spectroscopy
A
- Mathematical technique used to compute a spectrum from the FID
- A pulse is used to introduce non-equilibrium nuclear spin magnetization
- The relaxation of spins to their resonance is time dependent and measured to create the spectrum
3
Q
Carbon chemical shifts
A
- Carbon 13 is deshielded by electron withdrawing group
- The carbon is one atom closer to shielding or deshielding that group attached with H
- Carbon greater chemical shift compared to hydrogen
4
Q
Carbon compared to Hydrogen splitting
A
- Carbon has 20x of a shift compared to the hydrogen spectrum
5
Q
Peak areas depending on Carbon 13
A
- Not necessarily proportional to the number of carbons giving rise to those peaks shows carbon environment
- Carbon carbon splitting is ignored
6
Q
Proton Spin Decoupling
(Broadband-Decoupled Spectrum)
A
- H is continuously in resonance
- Average proton spin state shows the proton environment specifically single peak only shown
7
Q
Off-Resonance Decoupling spectrum
A
- 13C nuclei are only split by the protons directly bonded to them
- Shows peak area singlet, doublet and triplet
- TMS is a quartet at 0ppm
8
Q
Distortionless Enhanced Polarization Transfer (DEPT) NMR
A
- All peaks are decoupled singlets
- Has better sensitivity compared to the multiplets
- 13C nucleus is magnetically coupled to the protons bonded to it
- Polarisation transferdepending on protons bonded to carbon
9
Q
Interpreting 13C NMR Spectra
A
- The number of different signals implies how many different types of carbons are present
- The chemical shifts of those signals suggest what types of functional groups those carbon atoms belong to
- The splitting of signals in the Off-Resonance Decoupled, DEPT-90 and DEPT-135 spectra indicate how many protons are bonded to each carbon atom
