Illustrated Glossary of Organic Chemistry

Non-first-order splitting (second order splitting): In NMR spectroscopy, signal splitting due to non-first-order coupling. The n+1 rule is not obeyed; complex splitting patterns often result.

First order coupling
Jab = Jac

Non-first-order coupling
JabJac



First-order splitting results
The n+1 rule is obeyed
A triplet is observed

Non-first-order splitting results
The n+1 rule is not obeyed
A doublet of doublets is observed