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Phenyl Spectroscopy
Phenyl spectroscopy
Infrared spectroscopy
Since phenyl groups and aromatic rings have sp2 hybridized carbon atoms, the sp2 C-H stretch appears just above 3000 cm-1. For phenyl rings, aromatic overtones (zig zags) show up at 1800-2000 cm-1.
IR spectrum of ethyl benzene
NMR
In the 1H NMR, aromatic hydrogen atoms appear around δ6-δ8.
Proton NMR of toluene
In 13C NMR, the sp2 carbon atom peaks appear between δ100-δ150 where double bonded carbon atoms appear.
Carbon NMR of toluene
Mass Spectrometry
A very common cleavage in mass spectrometry is at the benzylic position to give a fragment of m/z = 91. We have seen earlier that benzylic cations are very stable because of resonance forms. In fact, benzylic cations can even rearrange to make an aromatic 7-membered ring cation called a tropylium ion.
Mass Spectrum of n-butylbenzene
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