Exercise 4 | Alkenes

For the following alkene molecules, predict the number of peaks in the alkene region of the 1H NMR, their splitting and the general range of coupling constants for each.
 

The protons of phenyl groups are not in the alkene region but in the aromatic region.

 

2 different alkene H ⇒ 2 signals
H see only 1 proton (H): doublet
H see only 1 proton (H): doublet
and H are trans: J (Hz) = 11-18 (Typical: 16Hz)

⇒ 2 doublets with a J ~ 16 Hz

 

2 alkene H but same environment ⇒ 1 signal
H and are equivalent and do not see any other proton: singlet

⇒ 1 singlet

 

2 different alkene H ⇒ 2 signals
H see only 1 proton (H): doublet
H see 3 protons (H and 2 H): triplet of doublet
H and H are cis: J (Hz) = 6-14 (Typical: 10Hz)

⇒ 1 doublet with a J ~ 10 Hz (for H) + 1 triplet of doublet J ~ 10 Hz and 6 Hz (for H)