The "ortho/para" rule applies here; substituents on the diene and the quinone will orient themselves to maximize electronic stabilization in the transition state. 3. Redox Chemistry (Reduction) Quinones are easily reduced to hydroquinones.
This is the most common reaction for substituted quinones. A nucleophile (like an amine, thiol, or alcohol) attacks the double bond. reactions of substituted quinones
Under UV light, substituted quinones can undergo [2+2] cycloadditions or abstract hydrogen atoms from solvents. This is frequently used in polymer chemistry and the study of DNA damage. The "ortho/para" rule applies here; substituents on the
Usually, the initial product is a hydroquinone. In the presence of excess quinone or air, this often oxidizes back into a new, substituted quinone. 2. Diels-Alder Cycloaddition Substituted quinones act as powerful dienophiles . Electronic Effects: Electron-withdrawing groups (like −CNnegative cap C cap N −CO2Rnegative cap C cap O sub 2 cap R This is the most common reaction for substituted quinones
) on the quinone accelerate the reaction by lowering the LUMO energy.
If the quinone has a good leaving group (like a halogen in p-chloranil ), a nucleophile can displace it directly. This is a common route for synthesizing complex dyes and bioactive molecules. 5. Photochemical Reactions
Electron-withdrawing groups make the quinone a stronger oxidant (easier to reduce). Electron-donating groups (like −OMenegative cap O cap M e −CH3negative cap C cap H sub 3 ) make the quinone more stable and harder to reduce.