Constant Selectivity Relationships of Addition Reactions of Carbanions

Abstract

The selectivities of stabilized carbanions towards electron‐deficient π‐electron systems are nearly independent of their reactivities, as shown by the rate constants of the reactions of nine carbanions 2 with four quinone methides 1. These constant selectivity relationships may constitute the basis of a nucleophilicity scale for carbanions.

Kinetische Untersuchungen von Carbokation-Carbanion-Kombinationen: Schlüssel zu einem allgemeinen Modell polarer organischer Reaktivität

“…In ‹bereinstimmung damit berichteten wir, dass bei den Reaktionen von 1 j (Tabelle 2) mit 2 f-NBu 4 , 2 f-K, 2 f-K/ [18]Krone-6 und 2 f-K/Kryptofix 222 (4,7,13,16,21,24-Hexaoxa-1,10-diazabicyclo[8.8.8]hexacosan) die gleichen Geschwindigkeitskonstanten beobachtet wurden. [3] Daher ergibt die Division der beobachteten Geschwin- [*] Prof. Dr Tabelle 2. Strukturformeln und Elektrophilieparameter der Chinonmethi-…”

“…Anders als bei fr¸her untersuchten Carbokation-Carbanion-Kombinationsreaktionen [8] spielen Einelektronentransferprozesse hier keine Rolle. [3] sowie in Tabelle 3 dieser Arbeit wurden nun verwendet, um ausgehend von Gleichung (1) die Elektrophilieparameter E der Chinonmethide 1 g ± m sowie die N-und s-Parameter der Carbanionen 2 a ± h zu berechnen. [9] Alle Geschwindigkeitskonstanten der Reaktionen der Carbanionen 2 a ± h in Lit.…”

Electrophilicity–Nucleophilicity Scale Also in the Gas Phase

“…The correlation between the nucleophilicities and pK a values of carbanions is quite poor [9] much like the correlation between the N gas values in Table 2 and gas-phase basicities. However, the correlation between Mayrs E values and the E gas values in Table 2 is reasonable for most of the electrophiles ( Figure 5, R 2 = 0.978).…”

Reactivity scales for quantifying polar organic reactivity: the benzhydrylium methodology

“…Plot of (lg k)/s N versus the nucleophilicity parameter N for the reactions of benzhydryl cations and quinone methides with p-nucleophiles (in CH 2 Cl 2 ) and carbanions (in DMSO). 17 that purpose, 15 as they can be considered as oxy-substituted benzhydrylium ions, which again have the same steric environment around the reaction center. In cases where the attack of the carbanions XYCH À at the quinone methides was reversible, Roland Lucius studied the reactions in the presence of excess CH acids XYCH 2 , which protonate the intermediate phenolate ions and thus give rise to second-order kinetics with rate-determining CC-bond formation (Scheme 3).…”

“…In cases where the attack of the carbanions XYCH À at the quinone methides was reversible, Roland Lucius studied the reactions in the presence of excess CH acids XYCH 2 , which protonate the intermediate phenolate ions and thus give rise to second-order kinetics with rate-determining CC-bond formation (Scheme 3). 15 Since in dilute DMSO solution the measured rate constants for the reactions of the potassium salts were not affected by 18-crown-6 additives and were identical to those measured for the corresponding tetrabutylammonium salts, we concluded that we were determining the reactivities of the free carbanions. A detailed study of the influence of counterions on the nucleophilicities of different types of carbanions was published recently.…”