Signal splitting and the (n + 1) rule
Additional structural information can be derived from the splitting pattern of each NMR signal. If the signal is split into 2 peaks, it is a doublet, 3 peaks is a triplet and 4 peaks is a quartet. If the signal is not split, it is a singlet. Splitting is caused by neighbouring atoms. In general, signals are split if there are H atoms on adjacent C atoms and the degree of splitting is given by the ‘(n + 1) rule’, where n is the number of equivalent H atoms on adjacent carbon atoms. The splitting pattern and the peak intensity ratios within split signals are given by Pascal’s triangle: doublet, 1 : 1; triplet, 1 : 2 : 1; quartet, 1 : 3 : 3 : 1; etc.