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Organic&bio. chem
NMR
| Question | Answer |
|---|---|
| Do all nuclei have spin? | No, only select nuclei have spin. |
| Da all nuclei have charge? | Yes, all nuclei have charge. |
| What produces a magnetic field? | A spinning, charged nucleus. |
| What is I? | Spin quantum number. |
| Calculating I: EVEN + EVEN | I= 0, can't use for NMR |
| Calculating I: EVEN + ODD | I = 1/2, 3/2, 5/2, ... |
| Calculating I: ODD + ODD | I = 1,2,3..... |
| In the spectrometer's magnet, the spins will align: | With or against the magnetic field. The two possibile spin states have different energies. (alpha low beta high) |
| The separation of a and B spin-states depends on: | The strength of the spectrometer's magnet. |
| ΔE = What is ɣ? | hv = h*(ɣ/2π)*Bo ɣ = gyromagnetic ratio |
| Resonance Frequencies for different nuclides are proportional to: | their gyromagnetic ratios (ɣ) |
| Continuous Wave NMR. RF source: Protons: | Irradiating RF source: low amplitude, fixed frequency, applied continuously. Spactrum trace recorded while magnetic field swept. Protons w/ different resonance freq. come into resonance sequentially. Slow! |
| Fourier Transform NMR. RF sources: Proton excitation: Time: | Short, powerful RF pulse. Excites protons w/ different resonance frequencies all at once (like a piano) Spin signals recorded vs. time when pulse is switched off. |
| What is the chemical shift? | Small changes in the resonance frequency due to shielding from the surrounding electrons. |
| δ(ppm) = | (Δν [Hz])/(Spectrometer operating frequency [MHz] ) |
| TMS: | tetramethylsilane - soluble in most organic solvents. |
| what is the purpose of a δ scale? | To make chemical shifts independent of the spectrometer's magnetic field. |
| For (1)H spectra, peak area is proportional to: | proportional to # of protons. |
| In the n+1 rule, what is n? | # of equally coupled protons. |
| What names are given to a carbon relative to the ipso carbon in order: | ortho, meta, para. |
| What does DEPT experiment stand for? | Distortionless, Enhancement, by Polarization Transfer. |
| What does DEPT do? | Enhances the intensity of signals, Provides information on the number of protons attached, Quarternary carbons are not observed. |
| In DEPT 135° pulse means: | Positive signals for CH and CH3 groups. Inverted signals for CH2. |
| In DEPT 90° pulse means: | Positive signals for CH groups. Null signals for CH2 and CH3 |
| In DEPT 45° pulse means: | Positive signals for CH CH2 and CH3 |
| δ(Cipso)= | 128.5 + δipso + E(δortho) + E(δmeta) + E(δpara) |
Created by:
Liarna9Joy
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