Quick answer
The number of signals in a ¹H NMR spectrum equals the number of chemically distinct (nonequivalent) sets of hydrogens in the molecule. Hydrogens related by symmetry — a mirror plane, a rotation, or free rotation — are equivalent and collapse into a single signal.
1. Each set of chemically distinct hydrogens gives exactly one signal.
2. Hydrogens equivalent by symmetry resonate at the same frequency and count as one signal.
3. Free rotation of a methyl group averages its three hydrogens into a single environment.
4. A mirror plane can make hydrogens far apart in the structure chemically identical.
5. To count, group every hydrogen into sets sharing the same connectivity, then count the sets.
Summary
Signals = distinct H sets · symmetry makes H's equivalent · mirror plane, rotation, free rotation · equivalent H's = one signal · group, then count.
Quiz yourself
Tap a question to reveal the answer — free, no login.
Its two methyl groups are related by a mirror plane, so all 6 hydrogens are chemically equivalent and resonate together.
Three — the CH₃, the CH₂, and the OH are three different environments.
All four hydrogens are made equivalent by the molecule's symmetry, so they share one environment.
Two — one for the two equivalent methyl groups and one for the four equivalent aromatic hydrogens.
Draw this on the whiteboard
Open the OChem Board whiteboard — benzene rings, wedge/dash bonds, and a clickable periodic table built in. No account needed.