Alkenes

Protons on alkenyl sp² carbons are somewhat deshielded and fall in the range of 4.0 to 7.0 ppm. They can have complex splitting patterns due to the different environments possible for these types of protons. In propene (CH₂=CH-CH₃), the protons are distributed across three distinct environments:

1. Vinyl Protons (CH₂=):
   • These protons appear in the range of 4.9–5.3 ppm.
   • They are split into two doublets due to coupling with the adjacent vinyl proton (H-C=), with a coupling constant (J) of ~10–18 Hz.
2. Vinyl Proton (H-C=):
   • This proton resonates in the range of 5.7–6.0 ppm.
   • It appears as a multiplet due to coupling with both the vinyl protons (CH₂=) and the methyl group (CH₃). The coupling constants are:
   • J (to CH₂=) ~10–18 Hz (cis/trans coupling).
   • J (to CH₃) ~6–8 Hz (allylic coupling).
3. Methyl Protons (CH₃):
   • These protons are more shielded and appear in the range of 1.6–1.9 ppm.
   • They form a doublet due to coupling with the adjacent vinyl proton (H-C=), with a coupling constant (J) of ~6–8 Hz.

propene