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Chapter 9 Ketones and Aldehydes Carbonyl Compounds Carbonyl Structure • Carbon is sp2 hybridized. • C=O bond is shorter, stronger, and more polar than C=C bond in alkenes. 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 9 4 Examples O O CH3 C CH CH3 CH3 Br 3-methyl-2-butanone 3-methylbutan-2-one 3-bromocyclohexanone O CH3 C CH CH2OH CH3 4-hydroxy-3-methyl-2-butanone 4-hydroxy-3-methylbutan-2-one Chapter 9 5 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 9 6 Examples CH3 CH2 CH3 O CH CH2 C H 3-methylpentanal CHO 2-cyclopentenecarbaldehyde cyclopent-2-en-1-carbaldehyde Chapter 9 7 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 CHO 3-methyl-4-oxopentanal 3-formylbenzoic acid Chapter 9 8 Common Names for Ketones • Named as alkyl attachments to -C=O. • Use Greek letters instead of numbers. O O CH3 CH3CH C CH CH3 C CH CH3 Br CH3 methyl isopropyl ketone CH3 a-bromoethyl isopropyl ketone Chapter 9 9 Historical Common Names O C O CH3 CH3 C CH3 acetophenone acetone O C benzophenone Chapter 9 10 Aldehyde Common Names • Use the common name of the acid. • Drop -ic acid and add -aldehyde. – – – – – 1 C: formic acid, formaldehyde 2 C’s: acetic acid, acetaldehyde 3 C’s: propionic acid, propionaldehyde 4 C’s: butyric acid, butyraldehyde. 5 C’s: valeric acid, valeraldehyde Br CH3 γ O CH CH2 β α C H -bromobutyraldehyde 3-bromobutanal Chapter 9 11 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 9 12 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 9 13 Formaldehyde • Gas at room temperature. • Formalin is a 40% aqueous solution. H H H O C H C O O C H O H heat H C H formaldehyde, b.p. -21C H2O HO OH H C H formalin trioxane, m.p. 62C Chapter 9 14 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 9 15 Synthesis Review • Oxidation – 2 alcohol + Na2Cr2O7 ketone – 1 alcohol + PCC aldehyde • Ozonolysis of alkenes. Chapter 9 16 Synthesis Review (2) • Friedel-Crafts acylation – Acid chloride/AlCl3 + benzene ketone • Hydration of terminal alkyne – Use HgSO4, H2SO4, H2O for methyl ketone Chapter 9 17 Aldehydes from Acid Chlorides Use a mild reducing agent to prevent reduction to primary alcohol. O CH3CH2CH2C O Cl LiAlH(O-t-Bu)3 Chapter 9 CH3CH2CH2C H 18 Ketones from Acid Chlorides Use lithium dialkylcuprate (R2CuLi), formed by the reaction of 2 moles of R-Li with cuprous iodide. 2 CH3CH2CH2- Li+ (CH3CH2)22-CuLi2+ + LiI + CuI O (CH3CH2CH2)2CuLi + O CH3CH2C Cl Chapter 9 CH3CH2C CH2CH2CH3 19 CARBONYL REACTIONS When adding electrophiles or nucleophiles, the stronger one adds first. In electrophilic addition the result is the oxonium ion which is stabilized by resonance giving a carbocation, which in turn is neutralized by an electrophile. In nucleophilic addition the result is the enolate ion and the negatively charged oxygen is quenched by an electrophile. The resultant product is the electrophile bonded to oxygen and the nucleophile bonded to the carbonyl carbon. Electrophiles and Nucleophiles An electrophile is an electron poor species, lacking a nobel configuration. A strong electrophile would contain a positive charge, i.e. a proton from an acid. Nucleophiles are electron rich substances with at least on nonbonding pair of electrons. Strong nucleophiles would have a negative charge. Nucleophiles HOH ROH NH3 HRRO- Electrophiles H+ FeCl3 AlCl3 BH3 CARBONYL REACTIONS 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 22 Addition of Water • In acid, water is the nucleophile. • In base, hydroxide is the nucleophile. • Aldehydes are more electrophilic since they have fewer e--donating alkyl groups. O H HO + H2O C H OH C H H K = 2000 a gemdiol O CH3 C HO + H2O CH3 CH3 OH C CH3 K = 0.002 a gemdiol Chapter 9 23 Addition of Alcohol Chapter 9 24 Mechanism • Must be acid-catalyzed. • Adding H+ to carbonyl makes it more reactive with weak nucleophile, ROH. • Hemiacetal forms first, then acid-catalyzed loss of water, then addition of second molecule of ROH forms acetal. • All steps are reversible. Chapter 9 25 Mechanism for Hemiacetal • Oxygen is protonated. • Alcohol is the nucleophile. • H+ is removed. Chapter 9 => 26 Hemiacetal to Acetal HO OCH3 + HO H OCH3 OCH3 + H+ + HOH HOCH3 OCH3 HOCH3 + CH3O H OCH3 CH3O OCH3 + Chapter 9 27 Oxidation of Aldehydes Easily oxidized to carboxylic acids. Chapter 18 28 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 9 29 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 30 4 SILVER MIRROR 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 32 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 Chapter 18 H 33 Tautormers Constitutional isomers in equilibrium with each other that differ in the location of a hydrogen atom and a double bond are called tautomers. A case of tautomerization occurs with ketones (aldehydes) that are in equilibrium with their enol form, which are called keto enol tautomers O OH Keto Form Enol Form ALDEHYDE AND KETONE REVIEW O Name H3C CH CH a. b. c. d. Cis-2-pentenal Cis-2-pentanal Trans-2-pentenal Trans-2-pentanal C CH2 H Answer a. b. c. d. Cis-2-pentenal Cis-2-pentanal Trans-2-pentenal Trans-2-pentanal The aldehyde is in position one. The double bond is trans. Name H3C CH2 O O C C CH2 a. 2-Oxobutanoic acid b.2-Butanone-1-carbaldehyde c. 2-Oxopentanoic acid d.3-Oxopentanoic acid OH Answer a. 2-Oxobutanoic acid b.2-Butanone-1-carbaldehyde c. 2-Oxopentanoic acid d.3-Oxopentanoic acid The carbon in the carboxylic acid is position one. Identify the chemical name for acetone. a. Methanal b.Ethanal c. Propanone d.Butanone Answer a. Methanal b.Ethanal c. Propanone d.Butanone Acetone is called propanone or dimethyl ketone. 1. CH3CH2MgCl + 2. H3O O C H3C a. 2-Propanone b.2-Butanone c. 2-Pentanone d.3-Pentanone H 3. Na2Cr2O7, H2SO4 Answer a. 2-Propanone b.2-Butanone c. 2-Pentanone d.3-Pentanone 2-Butanone is formed in the Grignard reaction. The secondary alcohol is oxidized to a ketone with sodium dichromate. O 1. CH3CH2Li C H3C a. 2-Propanone b.2-Butanone c. 2-Pentanone d.3-Pentanone OH + 2. H3O Answer a. 2-Propanone b.2-Butanone c. 2-Pentanone d.3-Pentanone The ethyl group adds to the carbonyl carbon. O 2 CH3CH2OH C H3C CH3 H+ a. 2,2-Diethoxypropane b.2-Ethoxy-2-propanol c. Propane-2,2-diol d.2-Ethoxypropane Answer a. 2,2-Diethoxypropane b.2-Ethoxy-2-propanol c. Propane-2,2-diol d.2-Ethoxypropane Two molecules of ethanol are added to the carbonyl, with loss of water. O 1. Ag(NH3)2, -OH H3C C CH2 H 2. H+ a. 1-Propanol b.Propanoic acid c. Propane-1,1-diol d.1-Hydroxypropanoic acid Answer a. 1-Propanol b.Propanoic acid c. Propane-1,1-diol d.1-Hydroxypropanoic acid The Tollens reagent reduces an aldehyde to a carboxylic acid. O H3C NaBH4 C CH2 CH3 a. 2-Butanone b.2-Butanol c. 2-Hexanone d.Butane CH3CH2OH Answer a. 2-Butanone b.2-Butanol c. 2-Hexanone d.Butane Butanone is reduced to 2-butanol. End of Chapter 9 Chapter 9 52