) on the quinone accelerate the reaction by lowering the LUMO energy.
Large groups can hinder the approach of the diene, often dictating which face of the quinone is attacked.
If the quinone is unsymmetrically substituted, the nucleophile typically attacks the less hindered carbon or the carbon with the lowest electron density. reactions of substituted quinones
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
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. ) on the quinone accelerate the reaction by
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
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 reversible redox cycle is how Coenzyme Q
This is the most common reaction for substituted quinones. A nucleophile (like an amine, thiol, or alcohol) attacks the double bond.