478 ENOLS AND ENOLATES 18.21 (a) 2-Methylpropanal has the greater enol content CH,,CHCH (CH3)2C=CH 2-Methylpropanal Enol fo Although the enol content of 2-methylpropanal is quite small, the compound is nevertheless capable of enolization, whereas the other compound, 2, 2-dimethylpropanal, cannot enolize it has no a hydrogens CH H ( Enolization is impossible. (b) Benzophenone has no a hydrogens; it cannot form an enol. Enolization is impossible.) Dibenzyl ketone enolizes slightly to form a small amount of enol C6HSCH,CCH C6H5 C6H-CH=CCH, C6H5 conjugation of the double bond with the remaining carbonyl group and by intramolecular hy drogen bonding. C6HSCCH,CCHs C6HsC CC6H5 propanone Enol form (d) The enol content of cyclohexanone is quite small, whereas the enol form of 2, 4-cyclo- hexadienone is the aromatic compound phenol, and therefore enolization is essentially Back Forward Main Menu TOC Study Guide Toc Student OLC MHHE Website18.21 (a) 2-Methylpropanal has the greater enol content. Although the enol content of 2-methylpropanal is quite small, the compound is nevertheless capable of enolization, whereas the other compound, 2,2-dimethylpropanal, cannot enolize— it has no hydrogens. (b) Benzophenone has no hydrogens; it cannot form an enol. Dibenzyl ketone enolizes slightly to form a small amount of enol. (c) Here we are comparing a simple ketone, dibenzyl ketone, with a -diketone. The -diketone enolizes to a much greater extent than the simple ketone because its enol form is stabilized by conjugation of the double bond with the remaining carbonyl group and by intramolecular hy￾drogen bonding. (d) The enol content of cyclohexanone is quite small, whereas the enol form of 2,4-cyclo￾hexadienone is the aromatic compound phenol, and therefore enolization is essentially complete. O Keto form OH Enol form (aromatic; much more stable) 1,3-Diphenyl-1,3- propanedione C6H5CCH2CC6H5 O O Enol form O C6H5C CH CC6H5 O H Dibenzyl ketone C6H5CH2CCH2C6H5 O Enol form C6H5CH CCH2C6H5 OH C O (Enolization is impossible.) C H CH3C CH3 CH3 O (Enolization is impossible.) 2-Methylpropanal (CH3)2CHCH O Enol form (CH3)2C CH OH 478 ENOLS AND ENOLATES Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website