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Organic Chemistry, 6th Edition L. G. Wade, Jr. Chapter 18 Ketones and Aldehydes Carbonyl Compounds => Chapter 18 2 IUPAC Names for Ketones • Replace -e with -one. Indicate the position of the carbonyl with a number. • Number the chain so that carbonyl carbon has the lowest number. • For cyclic ketones the carbonyl carbon is assigned the number 1. => Chapter 18 3 Examples O O CH3 C CH CH3 CH3 3-methyl-2-butanone 3-methylbutan-2-one Br 3-bromocyclohexanone O CH3 C CH CH2OH CH3 4-hydroxy-3-methyl-2-butanone 4-hydroxy-3-methylbutan-2-one => Chapter 18 4 Naming Aldehydes • IUPAC: Replace -e with -al. • The aldehyde carbon is number 1. • If -CHO is attached to a ring, use the suffix -carbaldehyde. => Chapter 18 5 Examples CH3 CH2 CH3 O CH CH2 C H 3-methylpentanal CHO 2-cyclopentenecarbaldehyde cyclopent-2-en-1-carbaldehyde => Chapter 18 6 Name as Substituent • On a molecule with a higher priority functional group, C=O is oxo- and -CHO is formyl. • Aldehyde priority is higher than ketone. COOH CH3 O CH3 O C CH CH2 C H 3-methyl-4-oxopentanal CHO 3-formylbenzoic acid Chapter 18 => 7 Historical Common Names C O CH3 O CH3 C CH3 acetophenone acetone O C benzophenone => Chapter 18 8 Boiling Points • More polar, so higher boiling point than comparable alkane or ether. • Cannot H-bond to each other, so lower boiling point than comparable alcohol. => Chapter 18 9 Solubility • Good solvent for alcohols. • Lone pair of electrons on oxygen of carbonyl can accept a hydrogen bond from O-H or N-H. • Acetone and acetaldehyde are miscible in water. => Chapter 18 10 Industrial Importance • Acetone and methyl ethyl ketone are important solvents. • Formaldehyde used in polymers like Bakelite. • Flavorings and additives like vanilla, cinnamon, artificial butter. => Chapter 18 11 Synthesis Review • Oxidation 2 alcohol + Na2Cr2O7 ketone 1 alcohol + PCC aldehyde • Friedel-Crafts acylation Acid chloride/AlCl3 + benzene ketone Chapter 18 12 Nucleophilic Addition • A strong nucleophile attacks the carbonyl carbon, forming an alkoxide ion that is then protonated. • A weak nucleophile will attack a carbonyl if it has been protonated, thus increasing its reactivity. • Aldehydes are more reactive than ketones. Chapter 18 => 13 Addition of Water • In acid, water is the nucleophile. • In base, hydroxide is the nucleophile. O H HO + H2O C H O CH3 C CH3 C H HO + H2O OH CH3 Chapter 18 H K = 2000 OH C CH3 K = 0.002 => 14 Addition of HCN • HCN is highly toxic. • Use NaCN or KCN in base to add cyanide, then protonate to add H. • Reactivity formaldehyde > aldehydes > ketones >> bulky ketones. O CH3CH2 C HO CH3 + HCN Chapter 18 CH3CH2 CN C CH3 15 => Formation of Imines • Nucleophilic addition of ammonia or primary amine, followed by elimination of water molecule. • C=O becomes C=N-R CH3 H3C RNH2 C O Ph R CH3 R _ C H2N O + Ph R Chapter 18 CH3 N C OH H Ph CH3 N C Ph N C OH H Ph R =>16 Other Condensations Chapter 18 => 17 Addition of Alcohol => Chapter 18 18 Mechanism • Must be acid-catalyzed. • Adding H+ to carbonyl makes it more reactive with weak nucleophile, ROH. • Hemiacetal forms first, then acidcatalyzed loss of water, then addition of second molecule of ROH forms acetal. • All steps are reversible. => Chapter 18 19 Mechanism for Hemiacetal • Oxygen is protonated. • Alcohol is the nucleophile. • H+ is removed. Chapter 18 => 20 Hemiacetal to Acetal HO OCH3 + HO H OCH3 OCH3 + H+ + HOH HOCH3 OCH3 HOCH3 + CH3O H OCH3 CH3O OCH3 + => Chapter 18 21 Cyclic Acetals • Addition of a diol produces a cyclic acetal. • Sugars commonly exist as acetals or hemiacetals. CH2 CH2 O O O + CH2 HO CH2 OH => Chapter 18 22 Acetals as Protecting Groups • Hydrolyze easily in acid, stable in base. • Aldehydes more reactive than ketones. O O CH2 CH2 OH HO C H + H C O O O => Chapter 18 23 Selective Reaction of Ketone • React with strong nucleophile (base). • Remove protective group. + _ MgBr O CH 3 O HO CH3MgBr C O O H3O C O O CH3 + C H O => Chapter 18 24 Oxidation of Aldehydes Easily oxidized to carboxylic acids. => Chapter 18 25 Tollens Test • Add ammonia solution to AgNO3 solution until precipitate dissolves. • Aldehyde reaction forms a silver mirror. O R C H + 2 + NH3)2 _ + 3 OH + Ag(NH3)2 _ + 3 OH O H2O O H2O 2 Ag + R C O _ 2 Ag + R C O + _ + 4 NH3 + 2 H2O => Chapter 18 26 4 Reduction Reagents • Sodium borohydride, NaBH4, reduces C=O, but not C=C. • Lithium aluminum hydride, LiAlH4, much stronger, difficult to handle. • Hydrogen gas with catalyst also reduces the C=C bond. => Chapter 18 27 Catalytic Hydrogenation • Widely used in industry. • Raney nickel, finely divided Ni powder saturated with hydrogen gas. • Pt and Rh also used as catalysts. O OH Raney Ni H => Chapter 18 28 End of Chapter 18 Chapter 18 29