37.4.2—The chemical shifts and splitting patterns

Chemical shift depends on the proton’s electronic environment: electronegative atoms and π systems usually deshield nearby protons. Splitting depends on neighbouring non-equivalent hydrogens.

Assign each proton set to a shift region, then count adjacent hydrogens and apply n+1 only when the sets are sufficiently equivalent for the simple model.

Protons next to an oxygen appear downfield from an ordinary alkyl group; a CH₂ next to CH₃ is commonly split into a quartet while the CH₃ is split into a triplet.

Do not predict splitting from the total number of hydrogens in the molecule or treat exchangeable OH/NH protons as fixed n+1 partners.