If by unpaired 'unpaired electrons' you mean paramagnetic species, then:
Paramagnetic species drastically reduces the relaxation times, which can be helpful in the T1 relaxation case, but when T2 is reduced a lot, your lines become exceedingly broad and hardly observable.
Dipolar coupling interactions are proportional to the product of gyromagnetic ratios of the interacting spins. The electron gyromagentic ratio is > 500x that of a proton, which is quite large compared to other NMR active nuclei, thus relaxation times are reduced.
In dependence of the molecule, you must to choose conditions of making spectrum: long time relaxation, smaller angle of pulse, etc.
In addition to what has already been said, you may think of the presence of the paramagnetic species as if you have added local strong magnets dispersed all over your sample, which spoils the magnetic field homogeneity throughout your sample. Lines are getting broad for that reason too, and nuclei spatially near the paramagnetic electrons are not even observable.
Markus M. Hoffmann could you please explain how paramagnetism causes a reduction in the NMR peaks height?
Budoor Al Umairi Unpaired electrons (paramagnetism) cause large fluctuations in local magnetic fields which is variable for each individual molecule. This means the ensemble of spins, which are ideally in-phase, will have different Larmor frequencies, depending on their local environment and orientation. This manifests as de-phasing, and this rate is related to the signal's FWHM. The faster the de-phasing, the larger the FWHM.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials Chemistry
- Polymer Chemistry