3.3.15 Nuclear Magnetic Resonance Spectroscopy Flashcards
What does NMR analysis provide information on?
The positions of 13C and 1H atoms in a molecule.
What is the reference compound all samples are measured against?
TMS, tetramethylsilane.
Where does the reference sample show up on the spectra?
At 0 ppm.
What is the x and y of an NMR spectra?
Y = absorption
X = chemical shift, ppm
Why is TMS used as a reference?
Non toxic, doesn’t react with the sample, easily separated from the sample due to a low BP, produces one strong sharp absorption peak on the spectrum.
What is the formula for TMS?
Si(CH3)4
What is the area under the peak?
The number of protons in a particular environment.
What causes a chemical shift of the absorption?
Different environments.
What are chemically equivalent protons?
Protons in the same chemical environment.
Each peak on an 1HNMR spectra relates to what?
To the protons in the same environment.
What do peaks on a low resolution NMR spectrum refer to?
The molecular environments of an organic compound
The strengths of the absorption lines are proportional to what?
The number of equivalent 1H atoms.
What is the splitting pattern of each peak determined by?
The number of protons on neighbouring environments.
What does the number of peaks a signal splits into =?
n + 1
What information do splitting patterns give?
Relative intensities.
The NMR spectronomer measures the area under each peak as what?
An integration spectra.
What is spin-spin splitting caused by?
A protons spin interacting with the spin stated of nearby protons in different environments.
What does spin spin splitting provide information on?
The number of protons bonded to adjacent carbon atoms.
For a proton with n protons attached to a carbon atom, the number of sub peaks in a splitting pattern =?
n + 1
Splitting patterns must occur in what? Why?
Pairs, because each proton splits the signal of the other.
What reference compound is used for 13CNMR?
TMS
On a 13CNMR spectra what are the peaks with different chemical shifts representative of?
The non-equivalent carbon atoms.
Does 13CNMR produce splitting patterns?
No.
In 13CNMR height is what?
Not proportional to the number of carbon atoms.
What solvents are samples dissolved in? Why?
Deuterated solvents or CCl4. Have even mass numbers so they have no spin and don’t interfere with 1HNMR.
