By Raimonds E. Valters, Wilhelm Flitsch (auth.), Alan R. Katritzky (eds.)
After learning ring-chain tautomerism of keto ami des and similar derivatives of functionalized carboxylic acids for greater than ten years, the authors think about it precious to summarize on hand effects on those prototropic equilibria. First makes an attempt to systematize the cloth have been released by means of Jones in 1963 (Chapter 1, ref. 11). a lot, occasionally contradictory, experimental information have been scattered concerning the literature at the moment; spectroscopic equipment, utilized to this box over the past twenty years, have been had to revise a number of prior strategies. within the following years certain features of ring-chain tautomerism were mentioned sometimes, yet no try out was once formerly made to hide the total box. This assessment is designed to supply a accomplished compilation of ring-chain tautomerism with one exception: carbohydrates that have already been taken care of time and again, were passed over. The publication is predicated on a monograph released in Russian: R. E. Valters, Ring-Chain Isomerism in natural Chemistry. Zinatne. Riga, 1978. There fore, the association and improvement of the subject is due usually to at least one of the authors (R.E.Y.). within the current paintings the literature has been coated till the tip of 1982.
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Extra info for Ring-Chain Tautomerism
Ring-chain equilibria are described for N -unsubstituted, N -methyl, N -ethyl, and N -phenyl-2-( 4-dimethylaminobenzoyl)benzami des , and also for N-(t-alkyl)-2-(2-imidazolylcarbonyl)benzamides  (see Table 14). The mechanism of the base-catalyzed equilibration may be as follows: By carrying out the isomerization in strongly basic solutions the anion of the hydroxylactam (3C) is formed; hydroxylactams (38) possess a stronger acidity (pKa - 12) than amides (3A) (pKa = 16-19). During acidification a fast protonization (3C) -+ (38) takes place.
Obviously, this order reflects the distances between the interacting groups. The Acylcarboxylic Acid Tautomeric Equilibrium Dependence on Solvents, Temperature, and Other External Factors. The influence of solvent properties on acylcarboxylic acid tautomeric equilibria has only rarely been studied. Polar solvents favor the cyclic form [31,32,68]. The mechanism of solvent effects on ring-chain equilibria (IA) +:! (18) is highly complex. Most important is the stabilization of the ring or chain form by intermolecular hydrogen bonds with the solvent molecules.
C ,/ II H /C ...... II Me /C ...... 8 ~ II Refs. 06 c 38 38 24 38 38 38 38 39 38 39 38 38 38 38 38 38 3000 e 38 I-Adamantyl Ph Me 4-MeOC 6 H4 4-MeC 6 H4 4-BrC 6 H4 4-CIC 6 H4 Ph H ...... C / KT R 4-MeOC 6 H4 4-MeC 6 H4 4-BrC 6 H4 4-CIC 6 H4 4-N02C 6 H4 H Me Et i-Pr I-Bu Ph 4-MeOC 6 H4 4-MeC 6 H4 4-BrC 6 H4 4-CIC 6 H4 3-MeC 6 H4 3-CIC 6 H 4 3-CF3 C 6 H 4 H 27 27 27 27 27 27 27 Intramolecular Reversible Addition to the C=O Group 27 3-Acylpropionic Acids and Substituted Derivatives (1a). The electrophiIi city of the carbon atom in the group RCO decreases in the series R = H, alkyl, aryl.
Ring-Chain Tautomerism by Raimonds E. Valters, Wilhelm Flitsch (auth.), Alan R. Katritzky (eds.)