A Practical Guide to First-Order Multiplet Analysis in ¹H NMR Spectroscopy

The ability to deduce the proper set of coupling constant (J) values from a complex first-order multiplet in a ¹H NMR spectrum is an extremely important asset. This is particularly valuable to the task of assigning relative configurations among two or more stereocenters in a molecule. Most books and treatises that deal with coupling constant analysis address the less useful operation of generating splitting trees to create the line pattern from a given set of J values. Presented here are general and systematic protocols for the converse, i.e., for deducing the complete set of J values from the multiplet. Two analytical methods (A, systematic analysis of line spacings, and B, construction of what can be called inverted splitting trees) are presented first. A reasonably thorough and systematic set of graphical representations of common doublet of doublets (dd's), ddd's, and dddd's are then presented. These constitute a complementary method for identification of J's through visual pattern recognition. These approaches are effective strategies for extraction of coupling constant values from even the most complex first-order multiplets.