ENOLS AND ENOLATES 471 18.2 As shown in the general equation and the examples, halogen substitution is specific for the a-carbon tom. The ketone 2-butanone has two nonequivalent a carbons, and so substitution is possible at both positions. Both 1-chloro-2-butanone and 3-chloro-2-butanone are formed in the reaction CHa CCH,CH3 CICH, CCH,CH3 CH3 CCHCH 2-Butanone Chlorine 1-Chloro. 2-butanone 3-Chloro-2-butanone 18.3 The carbon-carbon double bond of the enol always involves the original carbonyl carbon and the a-carbon atom 2-Butanone can form two different enols, each of which yields a different a-chloro slow CH3 CCH,CH HC=CCHCH CICH,CCH, CH 2-Butanone 1-Buten-2-ol (enol) 1-Chloro-2-butanone CH CCH.CH CHC=CHCH CH CCHCH 2-Butanone 18.4 Chlorine attacks the carbon-carbon double bond of each enol H,=CCH, CH3 CICH,-CCHCH CI CH3C-CHCH3 CH2C—Cl cl-Cl 18.5 (b) Acetophenone can enolize only in the direction of the methyl group CCH H, Acetophenone Enol form of acetophenone (c) Enolization of 2-methylcyclohexanone can take place in two different directions H3 CH OH lethylcyclohex-l-enol 2-Methylcyclohexanone 6-Methylcyclohex-l-en (enol form Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE WebsiteENOLS AND ENOLATES 471 18.2 As shown in the general equation and the examples, halogen substitution is specific for the -carbon atom. The ketone 2-butanone has two nonequivalent carbons, and so substitution is possible at both positions. Both 1-chloro-2-butanone and 3-chloro-2-butanone are formed in the reaction. 18.3 The carbon–carbon double bond of the enol always involves the original carbonyl carbon and the -carbon atom. 2-Butanone can form two different enols, each of which yields a different -chloro ketone. 18.4 Chlorine attacks the carbon–carbon double bond of each enol. 18.5 (b) Acetophenone can enolize only in the direction of the methyl group. (c) Enolization of 2-methylcyclohexanone can take place in two different directions. CH3 OH 2-Methylcyclohex-1-enol (enol form) CH3 O 2-Methylcyclohexanone CH3 OH 6-Methylcyclohex-1-enol (enol form) Acetophenone CCH3 O Enol form of acetophenone C CH2 OH OH CH3C Cl CHCH3 Cl OH CH3C CHCH3 Cl Cl OH ClCH2 Cl CCH2CH3 OH H2C CCH2CH3 Cl Cl CH3CCH2CH3 O 2-Butanone CH3C CHCH3 OH 2-Buten-2-ol (enol) CH3CCHCH3 O Cl 3-Chloro-2-butanone slow Cl2 fast CH3CCH2CH3 O 2-Butanone H2C CCH2CH3 OH 1-Buten-2-ol (enol) ClCH2CCH2CH3 O 1-Chloro-2-butanone slow Cl2 fast H CH3CCHCH3 O Cl 3-Chloro-2-butanone ClCH2CCH2CH3 O 1-Chloro-2-butanone Cl2 Chlorine CH3CCH2CH3 O 2-Butanone Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website