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.
Substituted quinones are some of the most versatile electrophiles in organic chemistry. Because the quinone core is electron-deficient, their reactivity is largely governed by the nature and position of the substituents ( -groups) attached to the ring. 1. Nucleophilic Conjugate Addition (Michael Addition) reactions of substituted quinones
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 This is a common route for synthesizing complex
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. Under UV light
Large groups can hinder the approach of the diene, often dictating which face of the quinone is attacked.
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.
This reversible redox cycle is how Coenzyme Q (Ubiquinone) transports electrons in the mitochondrial respiratory chain. 4. Nucleophilic Substitution ( SNArcap S sub cap N cap A r