Substitution reactions occur when two reactants exchange parts to give two new products. In a substitution, one replaces another

Quinones are an interesting and valuable class of compounds because of their oxidation-reduction, or redox, properties. The redox properties of quinones are important to the functioning of living cells, where compounds called ubiquinones(泛醌) act as biochemical oxidizing agents to mediate the electro-transfer processes involved in energy production

17.7 Lithium Enolates 17.8 α-Selenation: A Synthesis of α,β-Unsaturated Carbonyl Compounds 17.9 Additions to α,β-Unsaturated Aldehydes and Ketones

17.1 The Acidity of the α Hydrogens of Carbonyl Compounds: Enolate Anions 17.2 Keto and Enol Tautomers 17.3 Reactions via Enols and Enolate Anions

The most characteristic reaction of aldehydes and ketones is nucleophilic addition to the carbon-oxygen double bond

More reactive than benzene toward electrophilic substitution NO2 An deactivating group Less reactive than benzene toward electrophilic substitution Ortho-para director Meta director

The most characteristic reactions of benzenoid arenes are the substitution reactions that occur when they react with electrophilic reagents. The electrophiles are either a positive ion (E+) or some other electron-deficient species with a large partial positive charge

No addition of bromine No oxidation No hydroation Slow addition at high temperature and pressure

A UV-Vis spectrophotometer measures the amount of light absorbed at each wavelength of the UV and visible regions of the electromagnetic spectrum. λmax— the wavelength of maximum absorption

Conjugated unsaturated systems have a p orbital on a carbon adjacent to a double bond The p orbital can come from another double or triple bond The p orbital may be the empty p orbital of a carbocation or a p orbital with a single electron in it (a radical)