Illustrated Glossary of Organic Chemistry

First-order splitting: In NMR spectroscopy, signal splitting due to first order coupling. The n+1 rule is obeyed; 'normal' doublets, triplets, quartets, etc. 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