Chapter 15: NMR Spectroscopy

The magnitude of the energy gap depends on the strength of the imposed external magnetic field

Homotopic- protons are chemically equivalent and are interchangeable by rotational symetry Enantiotopic- protons are chemically equivalent and are interchangeable only by reflectional symmetry Diasterotopic- protons are not chemically equivalent and cannot be interchanged by symmetry

A signal is expected for each chemically equivalent hydrogen atom

A LEFT shift is described as DOWNFIELD and results from deshielded protons that absorb a higher frequency of rf radiation A RIGHT shift is described as UPFIELD and results from shielded protons that absorb a lower frequency of rf radiation− a lower frequency wave can penetrate further

• Divide each individual integration value by the smallest integration value • This gives the ratio of protons relative to each other • Compare the ratio of protons to the molecular formula to determine the number of protons in the compound

• Identify all chemically equivalent protons • Identify number of immediate neighbors for each equivalent proton; either geminal or vicinal • Apply the n+1 rule determine splitting

2H quartet and 3H triplet

1H septet and 6H doublet

9H singlet

Generally no splitting is observed across an alcohol oxygen atom Chemical shift ~2-5 ppm