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)?