June 21, 2011
by Arvin Moser, Team Manager, Application Scientists, ACD/Labs
Spin-spin splitting or J-coupling is used to elucidate and verify a candidate structure. The observed coupling pattern (also referred to as splitting or multiplet pattern) serves as a guide in determining the neighbouring groups. Hence, the wrong coupling pattern can send an elucidator on a wild-goose chase.
The following 1H NMR spectrum below is for an unknown compound. Is the coupling pattern most consistent with a quartet (q) or a doublet of doublets (dd) or an AB spin system poised as two doublets (d)?
Clearly, it’s not a quartet since J isn’t uniform . So it must be a doublet of doublet (dd) or two AB doublet. The peak intensities for a dd should be 1:1:1:1, so I bet for two AB doublet!