Long range spin-spin interactions in high resolution nuclear magnetic resonance and the concept of hyperconjugation

Indirect spin-spin couplings between methyl groups attached to unsaturated organic molecules and protons directly bonded to unsaturated carbon atoms have been observed in several molecules. An attempt is made to account in a qualitative way for the observed spin-spin couplings by ascribing them largely to hyperconjugation between methyl group orbitals and π-electron orbitals. The connection of these observations with electron spin resonance spectra is mentioned.