CHEM 214 Lecture 19: Lecture 19

• School: McGill University
• Department: Chemistry
• Course: CHEM 214
• Professor: Anthony Mittermaier

Document Summary

We apply rf pulse long enough such that we put the magnetization in the xy plane, then turn off rf pulse. Different nuclei in molecules precesses at different frequencies so we can detect signal from individual atoms. We could analyze nmr spectra in terms of raw frequency units, but this would be impractical. The larmor frequency of each nucleus depends on the local magnetic field (and for any spectrometer would be different, hard to compare from one group and another) wo=yb. The local electronic structure can be very slightly shielded nuclei from the static field = this is what allows different nuclei to be discriminated. We would be comparing frequencies that differ by just 1 or. Solution: introduce a chemical shift scale where the zero point is defined by the resonance frequency of a reference nucleus (methyl protons of tms or dss, charged readily dissolve in water).