, 1568 (1981).Protonation acidity constants for 27 benzamides, acetamides, and lactams have been determined. Ultraviolet, and I3C and 'H nmr, spectroscopic methods were used; almost all the spectra were found to be subject to medium effects, some quite severe, as the sulfuric acid concentration was increased. Despite this, the excess acidity (X-function) method gave accurate pKB,+ and m * values.In all cases protonation, followed by a medium shift in the spectrum of the protonated form, was the only process taking place; protonation was essentially complete in 60% H,S04. The results for the different bases are interpreted in terms of the resonance, inductive, and steric effects in operation in the acid and base forms. On a determine les constantes d'acidite de la protonation de 27 benzamides, acetamides et lactames. A cette fin on a utilise la rmn du 'H et du "C ainsi que la spectroscopie ultraviolette; lorsque la concentration en acide sulfurique augmente, presque tous les spectres subissent des effets de milieu qui sont quelquefois trbs importants. En depit decette influence, la methode d'excts d'acidite (fonction X ) donne des valeurs prkcises de pKBH+ et de m*. Dans tousles cas, la protonation, suivie d'un deplacement moyen dans le spectre de la forme protonee, est le seul processus qui a lieu; la protonation est tout a fait compl'ete dans du H,S04 a 60%. On interprbte les resultats des differentes bases en fonction de la resonance ainsi que des effets inductifs et steriques presents dans les formes acide et basique.[Traduit par le journal]

This paper is dedicated to Prof. Raymond U . Lemieux on the occasion of his 60th birthday PETER WAN, TOMASZ A. KEITH YATES. Can. J. Chem. 58,2423 (1980). The acid-catalysed hydrolysis of lactams of ring size 4-7, and of N-ethylacetamide, has been studied at various temperatures in 0-70% aqueous sulfuric acids. The kinetics have been analysed by means of the r-hydration parameter treatment and the transition-state activity coefficient (TSAC) approach. Except for the (3-lactam, all substrates show a strongpos~tiverate dependence on water activity, indicating a tetrahedral intermediate type of mechanism (A82), similar to that found for simple (acyclic) amide hydrolyses; only the (3-lactam shows a negative rate -water activity dependence, which is interpreted in terms of a unimolecular (Aal) mechanism, involving rate-determining acylium ion formation. Similarly, all substrates except the (3-lactam show a pronounced destabilization of the transition-state as ac~dity is increased, typical of oxonium Ion specles. The behaviour of the (3-lactam resembles that of methyl mesitoate hydrolys~s. Basicity constants for lactams of ring size 4-9 show a definite dependence on ring s u e , with the 6-lactam being unusually basic. Both rate and pK dependence on ring size are discussed In terms of ring strain and steric effects. The activat~on parameters, particularly AS*, are fully consistent with the conclus~ons drawn concerning transitionstate hydration.

The crystal and molecular structures of six quasi-phosphonium salts containing phosphorus-heteroatom (heteroatom = oxygen, sulphur or nitrogen) bonds were determined. Comparison of the molecular parameters obtained with those available for reference structures demonstrated that the 'double bond' character for the P'-Y bond decreases in the order Y = N w 0 > S.

Because of an error of about 0.1 Á in the coordinates of protons for which the dihedral angles are 180°, some of these results are corrections of those reported in ref 6. The major difference is that the coupling constant for = ' = 180°in Table I is increased by 0.65 Hz. The other values differ by 0.1 Hz or less. (37)

Formation constants for the hydrogen-bonded complexes between phenol (donor) and selected carbonyl or phosphoryl compounds (acceptors) were determined from IR Δν shifts. The P=O group is about two orders of magnitude stronger as an acceptor than the C=O group, but no evidence for the enolization of a β-diphosphoryl system was found. The IR absorption band of the phosphoryl group (νP=O) showed weak response to the involvement in the hydrogen bonding, and the shifts of the donor molecule (νOH) provide a better measure of the formation constants. Key words: carbonyl and phosphoryl groups as hydrogen bond acceptors, enolization of a β-difunctional system, determination of Kassoc from the IR Δνshifts.