Chem 334 1nd Edition Lecture 8Outline of Last Lecture I. Di and poly substituted reactionsOutline of Current Lecture II. Electrophilic Aromatic Substitution III. Carbonyl CompoundsIV. Oxidation of AlcoholsV. Organometallic CompoundsCurrent LectureElectrophilic aromatic substitution:Substituting compounds with more than one substituent already on them: Br2FeBr3 Br NO2When you begin with two substituents on a benzene ring, the ortho/para directing substituent wins overmeta directing one. If both are ortho/para directing, then the strongest activator dictates the position of the new substituent. O Br2FeBr3 Br These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. OONO2 ON NO Cl, AlCl3 O Sterics affects substitution. Substitution between two meta substituents usually doesn’t occur. HNO3/H2SO4 NO2 Cl + Br NO2 Br BrIn the reaction above, NO2 won’t substitute on carbon between the two substituents because of sterics.Carbonyl compounds:O Carbonyl groups consist of an oxygen attached to a carbon with a double bond. Some of the most common carbonyl compounds are aldehydes, ketones, carboxylic acids, esters, and amides.The oxygen of the carbonyl group carries a partial negative charge, while the carbon has a partial positivecharge. This makes the oxygen more electronegative than the carbon, making the carbon an electrophile, which can be attacked by nucleophiles. Some of the nucleophiles we will be using are H-, organo lithiums (R-Li), and Grignards (R-MgBr). PHPH OO ClClH- attack=reductionReduction is an increase in hydrogen content or a decrease in oxygen contentSodum Borohydride(NaBH4) (H-): NaBH4 is a weaker reducing agent that reduces aldehydes and ketones. O OH H NaBH4 NaBH4 with an aldehyde makes a primary alcoholO OH NaBH4 NaBH4 with a ketone makes a secondary alcoholOH H NaBH4 Lithium aluminum hydride (LiAlH4 or LAH): LAH is a strong reducing agent, meaning that it reduces a multitude of carbonyl compounds (aldehydes, ketones, esters, and carboxylic acids).O OH H LiAlH4 O OH LiAlH4 O OH O LiAlH4 OOOOOO OH OH LiAlH4 LiAlH4 Oxidation of alcohols:Oxidation is the opposite of reduction, meaning that it is an increase in oxygen content or a decrease in hydrogen content.Primary alcohols:OH OH O H OHSecondary alcohols:OH O Chromic Acid H2CrO4: H2CrO4 is a strong oxidizerOH O OH OH O (Potassium Permanganate KMnO4 is also a strong oxidizer)Pyridinium Chlorochromate (PCC): A pyridine is a six membered ring with a NH+ in ring. PCC works as a milder oxidizer. It stops primary alcohols at aldehydes.OH O OHOHOOO O[O][O][O]H2CrO4H2CrO4 PCCH OH O H OH PCC Organometallic compounds:Organometallic compounds are compounds that contain a carbon-metal bond, such as R-Li (organolithiums) and Gringnards. These compounds have very polarized bonds. Organolithiums have a strong negative charge on the carbon and strong positive charge on lithium (you can almost treat these compounds as R- and Li+). The same concept goes for Grignards (can be treated almost like R- +Mg-Br)(Remember following for exam synthesis!!)Synthesis of organolithiums:R-X + 2 Li Et2O or THF R-Li LiXIn the case above, X=Br, Cl, or IReactivity: R-I > R-Br > R-ClSynthesis of Gringnards:R-X Mg Et2O or THF R-Mg-XGrignards have the same reactivity as organolithiums
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