Summary
Summary Alevel Chemistry 1-H NMR Spectroscopy
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- AQA
1-H NMR Spectroscopy
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1-H NMR SpectroscopyAbout how hydrogen nuclei react to a magnetic field.
The nucleus of a hydrogen atom is a proton so the process is also know as proton NMR.
1H NMR tells you about the different hydrogen environments. It also tells you about about the
relative area under each peak and number of H atoms in each environment. The peaks give the
area ratio between the hydrogens in each environment.
The closer the atom is to an electronegative atom the greater the chemical shift.
Integration trace - the relative areas under the relative peaks.
Hydrogens on the same molecule have the exact same electronic signal.
3 lines could mean 4 carbons if two were in the same environments.
The splitting patterns occur because of the n+1 rule. If CH3 next to CH would have 2
because of the one hydrogen next to it + 1. The CH would have 4 peaks because 3+1.
Splitting Patterns
The peaks on a 1H NMR spectrum may be split into smaller peaks (spin-spin splitting). The split
peaks are called multiplets. Some have different splitting patterns.
Proton-free solvents
If the sample needs to be dissolved the solvent cannot contain H ions because they would show
up on the spectrum and confuse the readings.
Deuterated solvents are used where the H ions are replaced with D (deuterated solvents).
Deuterium is an isotope of hydrogen which has a neutron and proton. Deuterium does not
interact with the magnetic field and does not produce NMR peaks.
Examples are: CCl3D and OD2 (CCl4).
Reading NMR spectra
Number of peaks tells how many hydrogen environments are in a compound.
The ratio of peak areas states the number of relative of hydrogens in each environment.
The splitting pattern gives information on the number of hydrogens on the adjacent
carbon. The n+1 rule can be used to work this out.
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