Carbon‐13 NMR of quinone methides

The 13 C NMR spectra of four ortho ‐ and seven para ‐quinone methides were assigned using chemical shift and long‐range carbon‐proton coupling information. The carbonyl shifts are compared with those in ortho ‐ and para ‐benzoquinones. The chemical shifts of the carbonyls of the p ‐quinone methides are observed at δ 186.2–186.4 for the three ortho ‐di‐ tert ‐butyl‐substituted compounds and at δ 180.7–181.5 for the four ortho ‐oxy‐substituted compounds. In the three o ‐quinone methides with meta , para ‐dioxy substituents, the carbonyl signals are at δ 184.2–185.4. The carbonyl signal of the one o ‐quinone methide with no oxygen substitution is shifted downfield to δ 200.9, apparently as a result of hydrogen bonding to the nearby hydroxyl.