华南师范大学：《有机化学》课程PPT教学课件（双语版）Chapter 17 Aldehydes and ketones II. Aldol

Chapter 17 Aldehydes and ketones I. Aldol reactions 17.1 The acidity of the a-hydrogens of carbonyl compounds: Enolate ions (烯醇负离子) Nucleophilic addition nu R a-hydrogen B-hydrogens are not acidic are unusually acidic pka=40-50 (pka=19-20

Chapter 17 Aldehydes and ketones II. Aldol reactions 17.1 The acidity of the α-hydrogens of carbonyl compounds: Enolate ions （烯醇负离子） O R H H     - hydrogens are not acidic pka = 40 - 50 - Hydrogen are unusually acidic (pka = 19 - 20 Nucleophilic addition Nu: -

It can accept the proton to form the keto form, or it may accept the proton at oxygen to form an enol. B H Resonance-sta bilized anion HO Ht+ Enol fo (Unstable) Enolate .mml Keto form (Stable

It can accept the proton to form the keto form, or it may accept the proton at oxygen to form an enol. O H B: - O - -O H Resonance-stabilized anion O H Enolate HO O H H+ -H+ H + -H + Enol form Keto form (Unstable) (Stable)

17.2 Keto and enol tautomers (酮和烯醇互变异构体) Keto form Enol form Acetaldehyde CH3 H2c (-100%) ( almost 0%) OH Acetone CH H2c CH3 (99%) (0.00015% OH ycionexanone H (988%) (1.2%) OH O 2. 4-Pentanedione H3 C CH3 CCH, CCH3 CH3 C=CHCCH, The greater stability of the enol (76%) form

17.2 Keto and enol tautomers (酮和烯醇互变异构体） CH3 O H H2C OH H Keto form Enol form (- 100%) ( almost 0%) CH3 O CH3 H2C OH CH3 ( 99%) ( 0.00015%) O OH (98.8%) ( 1.2%) Acetaldehyde Acetone Cyclohexanone 2.4-Pentanedione CH3CCH2CCH3 O O CH3C=CHCCH3 OH O (24%) (76%) O O H H3C CH3 The greater stability of the enol form

17.3 Reactions via enols and enolate Ions 17.3 A Racemization(外消旋作用) Keto form ChG C2H OH CsH c CsH Or H3O k 5 H3C H HjCl H3C (R)-(+)-sec-Butyl phenyl ketone (+)-sec-Butyl phenyl ketone ( racemic form)(外消旋体) OH-1 Or H20 o→H ChG H3C a Acid or base can catalyze enolization Enol form

17.3 Reactions via enols and enolate ions 17.3A Racemization ( 外消旋作用) C O C6H5 Keto form C2H5 H3C H (R)-(+)-sec-Butyl phenyl ketone C O C6H5 C2H5 H3C H OH - Or H3O + + C O C6H5 C2H5 H H3C ( ± )-sec-Butyl phenyl ketone (racemic form)(外 消 旋 体 ） Enol form C O C6H5 C2H5 H3C H a b a b OH - Or H3O + Acid or base can catalyze enolization

17.3B Halogenation of ketones Ketones that have an a-hydrogen react readily with halogens by substitution. The rates of these halogenation reactions increase when acids or bases are added and substitution takes place almost exclusively at the a-carbon; X OH + x2 X Or H3O I

17.3B Halogenation of ketones Ketones that have an α-hydrogen react readily with halogens by substitution. The rates of these halogenation reactions increase when acids or bases are added and substitution takes place almost exclusively at the α-carbon; C O H OH - Or H3O + + X2 C O X + HX

Base-promoted Halogenation OH Enolate ion +X2 HX

Base-promoted Halogenation C O H OH - + X2 C O X + HX C O - C O - Enolate ion

Acid-Catalyzed halogenation OH Enol X X—X+C HX

Acid-Catalyzed Halogenation C O H C O X + HX C OH C O Enol H3O+ H X X +

17.4 The haloform reaction (卤仿反应) CH3 X2 Naoh ONa CHX3 +3H,O Haloform (鹵仿) CH3 Br2 Naoh ONa+ CHBr3 +3H,0 Bromoform (溴仿) cH3+2+NaOH—>〈 ONa+ CHI2+3H,O Iodoform (碘仿) Yellow precipitate Iodoform can test the stuctures of -coch3 or-CHOHCH3 If compound contain it, it give positive iodoform tests

17.4 The haloform reaction (卤仿反应） + X2 + NaOH O CH3 O ONa + CHX3 +3H2O Haloform （ 卤 仿 ） + Br2 + NaOH O CH3 O ONa + CHBr3 +3H2O Bromoform （ 溴 仿 ） + I2 + NaOH O CH3 O ONa + CHI3 +3H2O Iodoform （ 碘 仿 ） Yellow precipitate Iodoform can test the stuctures of –COCH3 or –CHOHCH3 If compound contain it, it give positive iodoform tests

The mechanism of the haloform reaction HGO CH,+ NaoH NaoH X—X CH2X CHX Nao X——X CHX2 CX3- + cX CHX3 +3H,0 OH ONa Holoform (卤仿)

The mechanism of the haloform reaction + NaOH O CH3 O OH + CHX3 +3H2O Holoform （ 卤 仿 ） O CH2 - - H2O X-X O CH2X NaOH O CHX - X X O CHX2 NaOH O CX2 - X X O CX3 NaOH O- OH CX3 + - : CX3 O ONa

17.4A The iodoform test The haloform reaction using iodine and aqueous sodium hydroxide is called the iodoform test Because it allows identification of the following two groups: (H) (H) R CH R—c—cH 3 (Ar) (Ar) OH Positive test for iodoform test

17.4A The iodoform test The haloform reaction using iodine and aqueous sodium hydroxide is called the iodoform test. Because it allows identification of the following two groups: R O CH3 R H C CH3 OH (H) (Ar) (H) (Ar) Positive test for iodoform test