Predict Splitting Patterns
The n+1 rule predicts how neighboring protons split an NMR signal: a proton with n equivalent neighbors on adjacent atoms appears as n+1 peaks. The highlighted protons are the signal; count their neighbors and pick the pattern. The answer key highlights those neighbors and explains the count.
Common Questions
What is the n+1 rule for splitting?
A set of protons with n equivalent neighboring protons on adjacent atoms is split into n+1 peaks. One neighbor gives a doublet (2 peaks), two a triplet (3 peaks), three a quartet (4 peaks), and so on. Equivalent protons do not split each other.
How do you predict a splitting pattern step by step?
Identify the signal's protons, then count all the hydrogens on the directly bonded neighboring carbons (n) — protons in the same equivalent set as the signal do not count. Apply n+1 to get the number of peaks: 0 neighbors is a singlet, 1 a doublet, 2 a triplet, 3 a quartet, 4 a pentet, 5 a sextet, 6 a septet.
Why is a CH₃ next to a CH₂ a triplet?
The CH₃ protons have two equivalent neighbors on the adjacent CH₂ carbon. By the n+1 rule, n = 2 gives 2 + 1 = 3 peaks, so the methyl appears as a triplet. In the same ethyl group the CH₂ has three neighbors from the CH₃, giving a quartet.
Do equivalent protons split each other?
No. Protons within the same chemically equivalent set do not split one another, so they are not counted as neighbors in the n+1 rule. Only equivalent protons on adjacent atoms in a different environment cause splitting.
When does the n+1 rule actually apply?
Strictly, n+1 applies when the neighboring protons all couple equally. When neighbors on different carbons are inequivalent but their couplings are similar — which is typical for freely rotating C–H chains — the peaks overlap into a single n+1 pattern called an apparent multiplet: 1-bromopropane's middle CH₂ sees 3H + 2H and shows an apparent sextet. These problems follow that convention and label such answers “apparent.” Protons within the same equivalent set never split each other.
Does an OH or NH proton split its neighbors?
Under typical conditions, no. OH and NH protons trade places with each other (and with traces of water) so quickly that their neighbors feel only an average, and the coupling washes out: ethanol's CH₂ appears as a clean quartet from the CH₃ alone. This coupling can reappear in rigorously dry solvent, which is why textbooks sometimes disagree. These problems never hinge on it — protons next to an OH or NH are simply never the highlighted target.