472 ENOLS AND ENOLATES 18.6 (b) Eno sization of the central methylene group can involve either of the two carbonyl groups CH CCHECCH C6HSCCH, CCH C6HSC=CHCCH Enol form 1-Phenyl-1, 3-butanedione Enol form 18.7(b) Removal of a proton from 1-phenyl-1, 3-butanedione occurs on the methylene group between the carbonyls C6H CCH, CCH, HO- CH_CCHCCH3 H,O The three most stable resonance forms of this anion are 0: O CBH_ CCH=CCH3 +CH_ CCHCCH C6HSC=CHCCH (c) Deprotonation at C-2 of this B-dicarbonyl compound yields the carbanion shown The three most stable resonance forms of the anion are 18.8 Each of the five a hydrogens has been replaced by deuterium by base-catalyzed enolization. Only the OCH, hydrogens and the hydrogens on the aromatic ring are observed in the H NMr spectrum at 3.9 ppm and 8 6.7-6.9 ppm, respectively CHO H, O CHaCCH, 5D0 KCO, CH,O CD.CCD, SDO 18.9 ax-Chlorination of (R)-sec-butyl phenyl ketone in acetic acid proceeds via the enol. The enol is achi- ral and yields equal amounts of (R)-and(S)-2-chloro-2-methyl-I-phenyl-l-butanone. The product is chiral. It is formed as a racemic mixture, however, and this mixture is not optically active m CHCH CHCH o CH C6HSC-CCH,CH3 (R)-sec-Butyl phenyl ketone Enol phenyl-1-butanone Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website472 ENOLS AND ENOLATES 18.6 (b) Enolization of the central methylene group can involve either of the two carbonyl groups. 18.7 (b) Removal of a proton from 1-phenyl-1,3-butanedione occurs on the methylene group between the carbonyls. The three most stable resonance forms of this anion are (c) Deprotonation at C-2 of this -dicarbonyl compound yields the carbanion shown. The three most stable resonance forms of the anion are: 18.8 Each of the five hydrogens has been replaced by deuterium by base-catalyzed enolization. Only the OCH3 hydrogens and the hydrogens on the aromatic ring are observed in the 1 H NMR spectrum at  3.9 ppm and  6.7–6.9 ppm, respectively. 18.9 -Chlorination of (R)-sec-butyl phenyl ketone in acetic acid proceeds via the enol. The enol is achi￾ral and yields equal amounts of (R)- and (S)-2-chloro-2-methyl-1-phenyl-1-butanone. The product is chiral. It is formed as a racemic mixture, however, and this mixture is not optically active. C C C6H5 HO CH3 CH2CH3 Enol C6H5C O CCH2CH3 CH3 Cl 2-Chloro-2-methyl-1- phenyl-1-butanone (50% R; 50% S) C O C6H5C H CH2CH3 CH3 (R)-sec-Butyl phenyl ketone acetic acid Cl2 K2CO3 CH2CCH3 5D2O CH3O CH3O O CD2CCD3 5DOH CH3O CH3O O O CH O O CH O O O CH H2O O H CH O O CH O HO O C6H5CCH O C6H5CCHCCH3 O O CCH3 C6H5C O O CHCCH3 O HO C6H5CCH2CCH3 C6H5CCHCCH3 H2O O O O O C6H5CCH CCH3 HO Enol form O O C6H5CCH2CCH3 1-Phenyl-1,3-butanedione OH O C6H5C CHCCH3 Enol form Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website