The α‐Effect: A Critical Examination of the Phenomenon and Its Origin

The synthesis and stereoelectronic structure of 1- and 2-(trimethoxysilylmethyl)- and 1- and 2-(silatranylmethyl)benzotriazole

“…The intrinsically most stable tautomer of benzotriazole is the 2H-, and the origin of the difference in stability with regard to the 1H-tautomer results in a balance between the lone-pair repulsion (6.5 kcal mol -1 ) [16][17][18] which favors the 2H tautomer and the aromaticity which favors the 1H tautomer. 1 The goal of our research is to synthesize the individual organosilicon BtH derivatives containing at the nitrogen atoms organosilicon substituents such as -CH 2 SiMe 3 (1 and 2), -CH 2 Si(OMe) 3 (3 and 4), and -CH 2 Si(OCH 2 CH 2 ) 3 N (5 and 6) 19 in position 1 or 2, and to study…”

Reactivity patterns of N-methylbenzhydroxamates. I. Studies of methyl transfer between N-methylbenzhydroxamates and arenesulfonates

“…Determining the expression of the cx effect can be done in two ways: (1) finding an extra reactivity in the cx nucleophile on a Brglnsted plot (P,,,), and (2) establishing the rate constant ratio of the cx nucleophile and a normal nucleophile of matched pKa (13,14). We decided to obtain the expression for the cx effect by direct competition of NMBH anions with pKa matched phenols, m-nitrophenol (pKa = 12.44) (1 5), and 3,4-dichlorophenol (pKa = 12.93) (15) in MeOH.…”

Medium effect on the α-effect for nucleophilic substitution reactions of p-nitrophenyl acetate with benzohydroxamates and m-chlorophenoxide in DMSO–H2O mixtures as contrasts with MeCN–H2O mixtures: comparing two very different polar aprotic solvent components

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] Thus, the enhanced nucleophilic reactivity shown by these nucleophiles was termed the α-effect by Edward and Pearson. 1 Since this definition only refers to the structure of the α-nucleophiles, an alternative operational definition was given to the α-effect, i.e., a positive deviation exhibited by an α-nucleophile from a Brønsted-type nucleophilicity plot.…”

“…1 Since this definition only refers to the structure of the α-nucleophiles, an alternative operational definition was given to the α-effect, i.e., a positive deviation exhibited by an α-nucleophile from a Brønsted-type nucleophilicity plot. 2 Numerous studies have been carried out to investigate the origin of the α-effect and many theories have been proposed to account for the cause of the α-effect, e.g., ground-state (GS) destabilization, transition-state (TS) stabilization through aromatic or radicaloid character, thermodynamic stability of the reaction products, and solvent effects. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] However, the effect of medium on the α-effect remains controversial although it has been studied most widely.…”

“…2 Numerous studies have been carried out to investigate the origin of the α-effect and many theories have been proposed to account for the cause of the α-effect, e.g., ground-state (GS) destabilization, transition-state (TS) stabilization through aromatic or radicaloid character, thermodynamic stability of the reaction products, and solvent effects. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] However, the effect of medium on the α-effect remains controversial although it has been studied most widely. [9][10][11][12][13][14][15][16][17][18] DePuy et al carried out the first gas-phase reaction of methyl formate with HOO -and HO -and found that HOO -does not exhibit higher reactivity than HO -9 and, on this basis, concluded that the α-effect shown by HOO -in aqueous reactions is due to solvent effect because HOO -was previously reported to be 12 kcal/mol less strongly solvated than HO -in H 2 O.…”