The α-Effect in Benzyl Transfers from Benzylphenylmethyl Sulfonium Salts to N-Methylbenzohydroamate Anions.

REACTIVITY OF NUCLEOPHILES AND Α-Effect IN SUBSTITUTION PROCESSES AT ELECTRON - DEFICIENCY CENTERS

“…There are two equivalent approaches to assess ing the magnitude of the αeffect: as the ratio of the rate constants k αnuc /k nuc or as the difference lg k αnuc -lg k nuc (k αnuc к and k nuc are, respectively, rate constants characterizing the reactivity of an αnucleophile and a "normal" nucleophile) at рК а αnuc ≈ рК а nuc . Usually, on the Brønsted de pendence, in reactions with electrophilic sub strates, the points for such typical αnucleop hiles as ClOand HOOions deviate upwards by 2-3 logarithmic units [1,2,6,9,10,15,16]. In this regard, when creating reagents that ef fectively break down ecotoxicants (mainly es ters of phosphorus and sulfur acids), the main efforts of researchers were focused on studying the nature of the αeffect [1, 2, 6, 9 , 10, 12-15], which remains one of the intriguing problems of modern physical organic chemistry.…”

“…At present, it is believed that αef fect can be responsible for: a) destabilization of the ground state of a nucleophile due to the re pulsion of lone electron pairs [17], b) stabiliza tion of the transition state [18,19], c) unusual thermodynamic stability of the reaction prod ucts [20][21][22][23] and d) differentiating solvation ef fects of the solvent [10,[24][25][26][27]. The magnitude of the αeffect can be influenced by a number of factors, including the nature of solvent [10,[24][25][26][27][28], the sensitivity of the standard series reactivity ("normal" anionic nucleophiles) to basicity (β nuc ) [8][9][10][11][12][13][14][15][16][17][18][19][20]23], type of hybridization of the electrophilic center [16,24,29,30].…”