Electrofugalities of 1,3-Diarylallyl Cations

Abstract

Heterolysis rate constants k1 of differently substituted 1,3-diarylallyl halides and carboxylates have been determined in various solvents. The linear free energy relationship log k1 = s(f)(N(f) + E(f)) was found to predict the heterolysis rates (log k1) of 1,3-diarylallyl derivatives with a standard deviation of 0.26, corresponding to a factor of 1.82 in k1, and maximum deviation in k1 of a factor of 5. Some systematic deviations are evident, however. Thus, 1,3-diarylallyl carboxylates always react faster and 1,3-diarylallyl chlorides always react more slowly than calculated by the quoted correlation equation when both types of leaving groups were used to determine the electrofugality parameters E(f). As 1,3-diarylalyl cations are generated faster in solvolysis reactions and also react faster with nucleophiles than benzhydrylium ions of similar thermodynamic stabilities, i.e., Lewis acidities, one can conclude that the reactions involving 1,3-diarylallyl cations proceed with lower intrinsic barriers than those involving benzhydrylium ions. The electrofugality parameters E(f) of 1,3-diarylallylium ions determined in this work were combined with the electrophilicity parameters E of the corresponding cations as well as with the results on ion pair dynamics reported in preceding papers for generating the full mechanistic spectrum of 1,3-diarylallyl solvolyses.

The ambident electrophilic behavior of 5‐nitro‐3‐X‐thiophenes in σ‐complexation processes

“…for the reaction of thiophene 2 with the CH 3 O − ion in methanol is 11.6 times larger than calculated () according to Equation . The deviations between calculated rate constants from the three parameters (Equation ) and experimental rate constants have been observed by many authors . Zenz and co‐workers investigated the reactivities of a series of trans ‐ β ‐nitrostyrenes with various acceptor‐substituted carbanions in dimethyl sulfoxide solution at 20°C and demonstrated that calculated rate constants according to the linear free energy relationship (Equation ) deviate by less than a factor of 6 from those measured.…”

“…They can also be employed for determining the electrophilicity parameters E of the two different positions of our thiophenes 1 and 2. [49][50][51][52][53][54][55][56][57] From the intercepts of these lines with the ordinate axis, values of the electrophilicity parameters E of unsymmetrical thiophenes 1 and 2 have been evaluated. For the addition to the 4-position, E values of -11.57 and -14.36 for the thiophenes 1 and 2 have been determined, respectively.…”

“…9 tion 1) and experimental rate constants have been observed by many authors. [54][55][56][65][66][67][68] Zenz and co-workers 66 investigated the reactivities of a series of trans--nitrostyrenes with various acceptor-substituted carbanions in dimethyl sulfoxide solution at 20 • C and demonstrated that calculated rate constants according to the linear free energy relationship (Equation 1) deviate by less than a factor of 6 from those measured. Breugst and co-workers 65 have shown that Equation 1 predicts the rate constants for reactions of amide anions with Michael acceptors in dimethyl sulfoxide solution within a factor of 2-21.…”

Nucleophilic Substitution Reactions of 2‐Methoxy‐3‐X‐5‐nitrothiophenes: Effect of Substituents and Structure–Reactivity Correlations

“…The linear free energy relationship given in Eq. (1) [1][2][3], in which the electrophile is characterized by a single parameter (E) and the nucleophile is characterized by two parameters (N, s), has been applied to Scheme 1 describe quantitatively the reaction rates of a large variety of electrophile-nucleophile combinations in which nucleophilic addition is rate limiting [3][4][5][6][7][8][9][10][11][12][13][14][15]. The electrophilicity scale thus established presently covers a reactivity range of 32 orders of magnitude, from E = −23.80 for substituted diethyl benzylidenemalonate 4 [16] to E = 8.02 for the 3,5-difluoro-substitued benzhydrilium ion 5 [17].…”

From QCA (Quantum Cellular Automata) to Organocatalytic Reactions with Stabilized Carbenium Ions

“…By selection of the right metals, the merging of enamine catalysis with Lewis acid‐catalyzed reactions would be possible 92. When we were investigating alcohols compatible in our organocatalytic alkylation, we immediately found out that 1,3 diphenyl allylic alcohol was not a reactive substrate, due to its high electrophilicity 93. So, it was not possible to generate the corresponding carbenium ion.…”