NMR stand for?
- Nuclear magnetic ressonance.
Which atoms will exhibit nuclear spin?
- Those with odd number of neutrons.
What happens to atoms with odd number of neutrons when passed through NMR machine?
- Exposed to magnetic field.
- Causes nuclei to flip
How does δ chemical shift scale read?
- From right to left.
2 types of NMR
Which gives simpler spectrum?
- ¹³C
- ¹H
- ¹³C gives simpler spectrum.
What is responsible for peak at δ= 0.0 on NMR spectra?
What is this called? Why is it used as this?
- Tetramethylsilane (TMS)
- Called: standard/ reference.
- Why: only has one C/ H environment.
What do each of peaks on ¹³C NMR spectrum show you?
- Number of carbon environments.
If you have electronegative atom, what side of spectrum would peak for H/ C close to this electronegative atom be?
- Greater chemical shift.
- Towards the left.
What does each peak on ¹H NMR spectrum show you?
- Number of different H environments.
Give 5 reasons why TMS used as a standard in NMR?
- Inert
- Non-toxic
- Volatile
- Same C/ H environments.
- Found to far right of spectrum.
Why is TMS being volatile useful?
- Can be easily removed once analsyis in complete.
2 different solvents used in NMR spectroscopy.
- CDCl₃
- CCl₄
Why are CDCl₃ + CCl₄ used as solvents in NMR spectroscopy?
- Will not interfere with with other ¹H peaks.
- No ¹H atoms –> no signals.
When would we use CDCl₃ VS CCl₄ as solvents in NMR?
- CDCl₃: polar so good solvent for polar organic compounds.
- CCl₄: non-polar so good solvent for non-polar organic compounds.
What is deuterium?
- Isotope of H.
- ²H
Name this: CDCl₃
- Deurated chloroform.
What does integration ratio tell you for ¹H NMR spectrum?
- RATIO of number of H’s in each H environment.
True or False
Inetgration ratio will tell you exact number of H’s in each H environment?
- False.
- Integration ratio will just give you the simplest ratio of number of H’s in each environment.
- This may SOMETIMES be exact same as number of H’s in each environment.
What do spin-spin splitting patterns in ¹H NMR tell you?
- n+ 1 rule.
- n = number of H on adjacent carbon.
If you have a
singlet
doublet
triplet
quartet
What does this tell you?
- Singlet: no H’s on adjacent C.
- Doublet: 1H on adjacent C.
- Triplet: 2H on adjacent C.
- Quartet: 3H on adjacent C.
What does area under peaks on ¹H NMR spectrum show?
- Tells you number of protons in particular environment.
What should you look out for in molecule with few C/ H environments?
- Symmetry.
Video example
compounds F and G have molecular formula: C₆H₄N₂O₄
Both are dinitrobenznes
F has two peaks in C13 nmr spec
G has three peaks in C13 nmr spec
give structures
-1,4-dinitrobenzene
- 1,2-dintrobenzene
What does largest m/z value tell you?
- Molecular ion peak.
- Mr of molecular formula of molecule.
