If the quinone is unsymmetrically substituted, the nucleophile typically attacks the less hindered carbon or the carbon with the lowest electron density.
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 reactions of substituted quinones
Large groups can hinder the approach of the diene, often dictating which face of the quinone is attacked. Electron-donating groups (like −OMenegative cap O cap M
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. Nucleophilic Conjugate Addition (Michael Addition)
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
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)