The α-Effect in S_NAr Reaction of 1-Fluoro-2,4-dinitrobenzene with Hydrazine: Ground-State Destabilization versus Transition-State Stabilization

Abstract

A kinetic study is reported on S N Ar reaction of 1-fluoro-2,4-dinitrobenzene with a series of primary amines including hydrazine in H 2 O at 25.0 o C. The plots of k obsd vs.[amine] are linear and pass through the origin, indicating that general-base catalysis by a second amine molecule is absent. The Brønsted-type plot exhibits an excellent linear correlation with β nuc = 0.46 when hydrazine is excluded from the correlation. The reaction has been suggested to proceed through a stepwise mechanism, in which expulsion of the leaving group occurs after the rate-determining step (RDS). Hydrazine is ca. 10 times more reactive than similarly basic glycylglycine (i.e., the α-effect). A five-membered cyclic intermediate has been suggested for the reaction with hydrazine, in which intramolecular H-bonding interactions would facilitate expulsion of the leaving group. However, the enhanced leaving-group ability is not responsible for the α-effect shown by hydrazine because expulsion of the leaving group occurs after RDS. Destabilization of the ground-state of hydrazine through the electronic repulsion between the nonbonding electron pairs is responsible for the α-effect found in the current S N Ar reaction.

Synthesis of Dipeptides and Ruthenium-Phenanthroline Derivative for Photo Redox Studies

“…On combining the 5 with 6 to gives the dipeptide 16 ester 7 in 60 % yield. The diester 7 on saponification gives dipeptide 17 2a in 75% yield. (scheme-1) Alternatively, dipeptide acid 2a was prepared from phthalimido ethanol 18 8, which on oxidation to acid product 19 9 followed by acid chloride 20 conversion gives 10 in 91% yield, which was esterified to MPM ester 21 11 by using MPM-OH, the phthalide group is cleaved by 40% monomethyl amine to get glycine MPM ester 22 12 in 55% yield.…”