Spectroscopy Tutorial: Alkenes and Conjugated Systems

IR Spectroscopy

In alkenes, the C-H stretch will be to the left of 3000. The C=C stretch appears as a medium band from 1680-1640.

NMR Spectroscopy

Alkene protons show up from 4.6–5.9 ppm. If the system is conjugated, they are shifted to 5.5–7.5 ppm.

A benzylic-conjugated proton (example below) can show up in the aromatic region.


Example 14