Spontaneous Cleavage of gem-Diazides: A Comparison of the Effects of .alpha.-Azido and Other Electron-Donating Groups on the Kinetic and Thermodynamic Stability of Benzyl and Alkyl Carbocations in Aqueous Solution

Intermediate obtained from photoionization, serving as precursor for the synthesis of Schiff’s base

“…This observation may be consistent with the conclusion that high barrier for the reaction of aniline with the carbocation in aqueous solution is composed primarily of water-aniline hydrogen bond [9]. Literature survey reflects that, apart from making the carbocations more selective by incorporating different electron-donating substituents (at para postion) in benzyl carbocations [2][3][4][5][6]8], the selectivity can also be enhanced by changing the solvent polarity. Even less selective benzyl carbocations can be made more selective (by changing the polarity of the solvent) and can proceed in two different paths or to react with two different nucleophiles.…”

“…All the while, our intent was to produce carbocations with high selectivity s = k nu /k H2O . Large values of selectivities are obtained when the reaction with nucleophile, Nu, is hastened and comes within the reach of diffusion controlled limited type reaction and the reaction with water is slow and approaches activation controlled type [2][3][4][5][6][7]. For example, the selectivity, s = k nu /k H2O is about 10 5 M -1 for reactions of triphenylmethyl carbocation (I) [8], 8,600 M -1 for α-azido-4-methoxybenzyl carbocation (II) [9] and 71,000 M -1 for 4-methoxy-α-(2,2,2-trifluoro)-thioethyl benzylcarbocation (III) [10].…”

“…For example, the selectivity, s = k nu /k H2O is about 10 5 M -1 for reactions of triphenylmethyl carbocation (I) [8], 8,600 M -1 for α-azido-4-methoxybenzyl carbocation (II) [9] and 71,000 M -1 for 4-methoxy-α-(2,2,2-trifluoro)-thioethyl benzylcarbocation (III) [10]. As the rate of the reaction of the carbocation with water increases, the selectivity decreases [2][3][4][5][6]8], approaching a value of about 6-100. When the reaction of the nucleophile, Nu, and water, (both with the carbocation) are either slow and activation controlled, or both are fast and diffusion-controlled, the selectivity, s, would turn out to be approximately same for the reactions with different carbocations in spite of their different intrinsic reactivities.…”

Effect of Hetero Atom on the Hammett’s Reaction Constant (ρ) from the Physical Basis of Dissociation Equilibriums of (Dithio) Benzoic Acids and (Thio) Phenols and Its Application to Solvolysis Reactions and Some Free Radical Reactions

“…An effect of α-hetero atom substitution on kinetic and thermodynamic stability of intermediate carbocations were also reported from elsewhere [6,7] and from our laboratory [8]. But in these reactions [3][4][5] no attempt is made to explain the effect of α-hetero atom on the Hammett reaction constant (ρ), which we tried to explain in the present work taking the title equilibriums as staple examples.…”

“…However the readers can find many articles and reviews in several standard physical-organic chemistry text books. In addition to these numerous reactions, a few reactions were reported by one of the authors (V. Jaganndham) from elsewhere [3] and from our laboratory [4,5] on the solvolysis and reactions of intermediate carbocations with nucleophilic solvent water. An effect of α-hetero atom substitution on kinetic and thermodynamic stability of intermediate carbocations were also reported from elsewhere [6,7] and from our laboratory [8].…”