NMR Spectroscopy Flashcards
How is NMR carried out
- sample must be dissolved in a solvent
- 1H must not be present in the solvent
- add a standard (Tetramethylsilane) and set peak to 0ppm Chemical shift δ on x-axis
- carry out a carbon (C13) NMR or a proton (H^1) NMR
What solvent should be used if the sample is either polar or non-polar
polar: CDCl3
non-polar: CCl4
Why is D (deuterium) used instead of H in the solvent
The nucleus of H contains 1 proton.
- This is an odd number of nucleons so its magnetic and NMR will be active which produces asignal therefore it will interfere with the spectrum
Nucleus of D contains 1 neutron and 1 proton
- even number of nucleons so is not magnetic
Why is tetramethylsilane added to samples
- non toxic
- inert > doesn’t react w/ sample
- gives one peak by 1H or C13 NMR
- volatile
all H and C are in the same environment
What dies the number of peaks in a C13 NMR show?
number if peaks is equal to the no. of different carbon environment
no. of peaks ≠ no. of carbons if there is symmetry
What determines the shift in C13 NMR
the environment that each carbon is in determines the shift of each peak
What does it mean if an atom is not symmetrical
every carbon will have a unique environment
How does a methyl group affects peaks
if there are an even number if methyl groups on the same carbon they will be in the same environment due to symetry sroung the tertahedral c
- will give a rise to 1 peak
What is the number of peaks relative to in 1H NMR
Number of peaks = number of different H environments
What is the methyl trick with H NMR
- if there are a number of hydrogens on the same carbon they will be in the same environment due to symmetry around the tetrahedral c and will give a rise to 1 peak
- if there are a number of methyls on the same carbon all the hydrogens in the methyl groups are in the same environment and give arise to 1 peak
What is an integration value
relative numebr of protons (H) there are in a particular environment
(area under the curve)
- tell us the relative ratio of protons
What is a splitting pattern
how many protons (H) there are on the adjacent C atom
gaps between peaks can help calculate splitting pattern
How can you calculate the relative number of H atoms from peaks
divide each value by the smallest number
What is a singlet
has zero hydrogens on the adjacent carbon
What is a doublet
there is 1 hydrogen on the adjacent carbon
What is a triplet
there are two hydrogens on the adjacent carbon
What is quartet
there are 3 hydrogens on the adjacent carbon
