Perspectives on Structure and Mechanism in Organic Chemistry by Carroll Felix A

Author:Carroll, Felix A.
Language: eng
Format: epub, pdf
Publisher: John Wiley & Sons
Published: 2011-08-23T16:00:00+00:00

The equilibrium favors the hydroxy form in the gas phase and the keto form in polar solvents. In nonpolar solvents both tautomers are present in comparable concentrations. For leading references and a theoretical study, see Wong, M. W.; Wiberg, K. B.; Frisch, M. J. J. Am. Chem. Soc. 1992, 114, 1645.

159 An exception to this generalization is the elimination of trihalomethyl anion in the haloform reaction (Figure 7.10).

160 For reviews, see (a) Euranto, E. K. in Patai, S., Ed. The Chemistry of Carboxylic Acids and Esters; Wiley-Interscience: London, 1969; pp. 505–588; (b) Koskikallio, J. in Patai, S., Ed. The Chemistry of Carboxylic Acids and Esters; Wiley-Interscience: London, 1969; pp. 103–135; (c) Kirby, A. J. in Bamford, C. H.; Tipper, C. F. H., Eds. Comprehensive Chemical Kinetics. Volume 10. Ester Formation and Hydrolysis and Related Reactions; Elsevier Publishing: Amsterdam, 1972; pp. 57–207; (d) Talbot, R. J. E. in Bamford, C. H.; Tipper, C. F. H., Eds. Comprehensive Chemical Kinetics. Volume 10. Ester Formation and Hydrolysis andRelated Reactions; Elsevier Publishing: Amsterdam, 1972; pp. 209–293.

161 According to the 1989 IUPAC Recommendations for the Representation of Reaction Mechanisms (Commission on Physical Organic Chemistry, IUPAC Pure Appl. Chem. 1989,56,23; also see Guthrie, R. D.; Jencks, W. P. Acc. Chem. Res. 1989,22,343), bond-making (association) processes are denoted A, while bond-breaking (dissociation) processes are labeled D. An electrophilic or electrofugic process at a core atom is indicated with a subscript E, and a nucleophilic or nucleofugic process at a core atom is shown with a subscript N. Subscript H indicates hydron as electrophile or electrofuge at a core atom, and subscript h indicates a hydron as electrophile or electrofuge at a peripheral atom. Stepwise processes are indicated using a plus sign (+). Using this formalism, the AAc1 mechanism is denoted as Ah + DN + AN + Dh. The AAc2 mechanism is denoted Ah + AN + AhDh + DN + Dh. The AAl1 reaction is called Ah + DN + AN + Dh.

162 Other mechanistic designations are possible. For a discussion of the B-AAc3 mechanism, for example, see Kanerva, L. T.; Euranto, E. K. J. Chem. Soc. Perkin Trans. 2 1986, 721.

163 Bender, M. L.; Ladenheim, H.; Chen, M. C. J. Am. Chem. Soc. 1961, 83, 123.

164 Figure 7.18 shows a mechanism proceeding through protonation of the carbonyl oxygen, which is generally agreed to be the predominant site of protonation of an ester. (Compare reference 160c.) Protonation of the alkyl oxygen also occurs to some extent, and an alterative mechanism involving this pathway can be written (reference 112).

165 Yates, K. Acc. Chem. Res. 1971, 4, 136.

166 To facilitate the interpretation of acid-catalyzed hydrolysis reactions, Yates defined an r value:

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