Enols and Other Reactive Species

Abstract

Rapid advances in the chemistry of enols and other reactive species have been made possible recently by the development of methods for generating these short-lived substances in solution under conditions where they can be observed directly and their reactions can be monitored accurately. New laboratory techniques are described and a sample of the new chemistry they have made available is provided; special attention is given to ynols and ynamines and the remarkable effects that the carbon-carbon triple bonds of these substances have on their acid-base properties.

Asparagine 229 in thymidylate synthase contributes to, but is not essential for, catalysis.

“…However, Gerlt et al (35,36) have pointed out that proton transfer to carbonyl oxygen can be assisted by weak acids if the pKa of the resultant enol is close to that of the general acid and if the proton transfer is late in the transition state. We do not know the pKa of enol intermediate 2, but based on the most appropriate models available, we estimate it to be at least 12 (37). Thus, in this context, the asparagine amide group (pKa 15.1, estimated from acetamide) (38,39) and water (pKa = 15.7) could serve as electrophilic catalysts and in stabilization of the negatively charged 0-4 of the intermediates.…”

Generation and study of enols and other reactive species

“…In order to determine just how much that is, we have examined this keto-enol system (ref. 29). We generated the enol from the corresponding bis-mmethyisilyl derivative, eq.…”

Mass spectral and theoretical studies on the tautomerism of selected thioesters

“…The carbonyl-enol equilibrium constants are generally very low for carbonyl compounds which do not carry strong electron-withdrawing groups or conjugating substituents [1][2][3][4] . pK Enol values are much lower for enols with β-electron-withdrawing groups, such as C=O and the enol form is frequently observable.…”