Ambident nucleophilic reactivity. 9. Regioselectivity in the reaction of ambident phenoxide ion and methoxide and hydroxide ions with 2,4,6-trinitroanisole. Kinetic and thermodynamic control

AM1 studies on the stabilities of anionic σ-complex regioisomers: thermodynamics of regioselectivity in the reaction of methide, methoxide, and hydroxide anions with electron-deficient aromatics

“…The kinetic preference (kl vs. k3) shown by nucleophiles in such reactions with 2, as well as the thermodynamic stability of the adducts (K1 = kllkPl vs. K3 = k3/kP3), yield patterns of regioselectivity that have constituted an important area of recent inquiry (7,8). In the course of these investigations we have classified the various types of potential regioselectivity3 in MC formation for 1-X-2,4,6-trinitrobenzenes (7), ranging from thermodynamic and kinetic preference for formation of MC-1 (termed KlT1, and exemplified by the reaction of TNA with phenoxide as an 0-nucleophile) (7a), among other systems (9, lo), to the more commonly reported kinetic preference for MC-3 formation, coupled with formation of MC-1 as the product of thermodynamic control, i.e., K3T1 as illustrated by the TNAalkoxide systems (5, 1 1).…”

“…In the course of these investigations we have classified the various types of potential regioselectivity3 in MC formation for 1-X-2,4,6-trinitrobenzenes (7), ranging from thermodynamic and kinetic preference for formation of MC-1 (termed KlT1, and exemplified by the reaction of TNA with phenoxide as an 0-nucleophile) (7a), among other systems (9, lo), to the more commonly reported kinetic preference for MC-3 formation, coupled with formation of MC-1 as the product of thermodynamic control, i.e., K3T1 as illustrated by the TNAalkoxide systems (5, 1 1). Most recently we have detailed K 1T3 regioselectivity in the TNA -mesitoxide system (7b), the exact inverse of K3T 1 behaviour (7).…”

“…For example, ab initio calculations at the S T O -3~ 30ur ~revious terminology for KIT1 (Kinetic preference for C-1 level have been run to delve into the question of structure of attack, coupled with Thermodynamic preference for C-1 attack) was cyclohexadienate anions: planar or fully delocalized in a KC-1,1, indicating Kinetic Control favouring MC-I formation (7). KlTl now replaces KC-1,l and similarly KC-1,3 is now designated as homocyclopentadienyl structure (17, 18).…”

Can t-BuOK be a good nucleophile? An ion-pairing answer. Cleavage of aryl ethers in their cationic iron complexes

“…Nucleophilic reactions are all the easier as the 12-electron organometallic moiety is more electron withdrawing (Cr(CO) 3 < (FeCp) + < Mn(CO) 3 + ). [20][21][22] The CpFe + fragment is excellent for this purpose, because its cationic form provides a strong activation, and these 18-electron complexes …”

σ-Complexes as biochemical and biophysical probes. Part 6. The interaction of N-2,4,6-trinitrophenyl-L-lysine with methoxide ion in dimethylsulfoxide-methanol (95%-5% v/v) mixture: proton transfer and σ-complex formation

“…Our study 8 of the interaction of the dinitroaniline herbicides, trifluralin and benefin, with hydroxide and sulfite ions has firmly established the formation of anionic σ -adducts by these compounds; structures of the derived species and the pathways for their formation were elucidated. σ-Complexes are recognized as models of the reaction intermediates postulated for nucleophilic aromatic substitution (S N Ar) processes [1][2][3]11,12 . A number of structure-reactivity relationships involving these species have been elucidated; the kinetic and thermodynamic data for the formation and decomposition of the σ-complexes, which have aided the understanding of the mechanism of S N Ar reactions, have been the subject of authoritative reviews [1][2][3] .…”