Quaternary Nitrogen Heterocycles. V. Substituent Effects on the Equilibrium Constants for Pseudobase Formation from Quinolinium and Isoquinolinium Cations

Abstract

Equilibrium constants (pKRoH) have been measured for pseudobase formation from the 1-methyl-x-nitroquinolinium cations (x = 5-8), the N,N1-dimethyl-1,5-, -1,6-, a n d -2,7-naphthyridinium dications and various N-substituted quinolinium, isoquinolinium, 5-nitroisoquinolinium, and 1,8-naphthyridinium cations. The pKRoH values for N-substituted 5-nitroisoquinolinium and 1,s-naphthyridinium cations are correlated by the equations pKRoH = -3.7cr* + 11.6 and pKRoH = -4.9cr* + 12.5, respectively (cr* is Taft'ssubstituent constant for the substituent on nitrogen).Proton magnetic resonance and u.v. spectral data have been used to assign the structures of the pseudobases formed from each of the above cations. In several cases ylide formation rather than pseudobase formation has been observed. The N,N1-dimethylnaphthyridinium dications are shown to form zwitterionic alkoxide ions in strongly basic aqueous solution, rather than undergoing attack by a second hydroxide ion.Equilibration between cation and pseudobase occurs at rates near or beyond the limit of the stopped-flow technique for all the above cations, except the 2-cyanomethyl-5-nitroisoquinolinium cation. An analysis of the pH--rate profiles for reversible pseudobase formation from this latter cation is given.On a determine les constantes d'tquilibre (pKRoH) pour la formation de pseudobases a partir des cations mtthyl-1 nitro-x quinoleiniums (x = 5-8) des dications N,N'-dimethyl naphtyridiniums-1,5, -1,6, -2,7, et de divers cations N-substitutts quinoleiniums, isoquinoleiniums, nitro-5 isoquinolCiniums et naphtyridiniums-1,s. On a relit les valeurs de pKRo,, des cations N-substituts nitro-5 isoquinoltiniums et naphtyridiniums-1,s par les equations suivantes: pKROH = -3.7cr* + 11.6 et pKRoH = -4.9cr* + 12.5 (cr* est la constante de substituant de Taft pour le substituant sur l'azote).On a utilist les spectres r.m.n. et u.v. pour attribuer les structures des pseudobases obtenues de chaque cation mentionnt ci-haut. Dans plusieurs cas on a observe la formation d'ylides plutBt que de pseudo-bases. On a montre que les cations N,N1-dimethyl naphtyridiniums forment, dans des solutions fortement basiques, des alcoolates ampholytes au lieu de subir une attaque par un second ion hydroxyde.Pour tous les cations ttudits, except6 le cation cyanomtthyl-2 nitro-5 isoquinoleinium, l'equilibre se fait a une vitesse proche ou au-dela de la limite d e la technique a dtbit arr&tC. On mentionne une analyse de la courbe de p H pour la formation rdversible de pseudobase i~ partir de ce cation.[Traduit p a r le journal]Can. J. Chem., 52,962 (1974)As a further extension of our quantitative studies (1, 2) of pseudobase formation from heteroaromatic cations, we now wish to present equilibrium data for some substituent effects on pseudobase formation from substituted quinolinium, isoquinolinium, and related cations. In addition to measuring pKRoH values for each cation, in each case we have investigated the reaction by U.V. and p.m.r. spectroscopy to ensure that pseudobase formation is the pre...

The pseudobase behaviour of 1,3-disubstituted-1,2-dihydro-2-oxopyrimidinium cations

“…For the series of cations 18 (R = Ph, PhCH2, Me, Et, c-Hex, i-Pr, tert-Bu) least-squares fitting of the data gives with a correlation coefficient of 0.985 for seven values. The value of p* = -3.6 is very close to those found by Bunting and Meathrel (4), and by Lindquist and Cordes (6). Both our value and those of Bunting and Meathrel must involve a steric component.…”

“…The more negative p* = -4.2 is due to steric effects since the OH group of the pseudobase 12 is necessarily next to the substituent R. Again, however, the value is close to those found by other workers (4,6).…”

Mechanism of bromination of a quaternary pyrimidinium cation. Change of rate determining step with acidity

“…The approach to equilibrium follows first-order kinetics and the observed rate constant k,,, is the sum of the rate constants for formation (k,) and decomposition (k,) of the pseudobase QOH. Finally, with respect to the reactivity of Q + and Q O H in equilibration, we point out that the rate constants we have obtained are very similar to those which Bunting and Meathrel (12) found for the 2-cyanomethyl-5-nitroisoqui~~olium cation (4) and its pseudobase. Of the many cations they studied, the cation 4 has a value of pKR-most similar to that of Q t .…”

Rates and equilibriums for hydroxide ion addition to quinolinium and isoquinolinium cations

“…Br" 185-186 4.0 (3 H, s), 6.1 (2 H, s), 7.1 (2 H, d), 7.6 (2 H, d), 8.2 (1 H, t), 8.8 (2 H, t), 9.1 (1 H, d), 9.3 (1 H, d), 7.4 (4 H, q), 8.2 (1 H, t), 8.8 (2 H, t), 9.05 (1 H, d), 9.25 (1 H, d), 10.1 (1 H, s) (C17H15BrN,0,), CHN H Br-208-209 6.2 (2 H, s), 7.6 (4 H, t), 8.25 (1 H, t), 8.9 (2 H, t), 9.1 (1 H, d), 9.3 (1 H,d),10.15 (1 H, s) (C16H13BrN204), CHN…”