Reactivity of Water and Alcohols toward Carbocations Generated in the Photolysis of 2,2,4,6-Tetramethyl-1,2-dihydroquinoline

Effect of microheterogeneity of CF3CH2OH-H2O mixed solvent on reactions of carbocations from 1,2,2,3-tetramethyl-1,2-dihydroquinoline

“…[14] This explanation is not valid for the dependence with a maximum observed for 1 in TFE-H 2 O mixtures, because H 2 O is much stronger nucleophile and base than TFE, and consequently the rate constant of the carbocation decay should monotonically increase as the concentration of H 2 O increases as observed for 4-methylsubstituted DHQ 2 (Fig. 3b).…”

“…[16] As was found before for the carbocations from DHQ, the activation energy of the combination with alcohols is lower than that with water by 10-15 kJ mol -1 and monotonously changes with solvent composition. [9,10,14] The minimum in the activation energy in the case of the carbocation from 1 in the TFE-H 2 O mixture 3 : 7 (19 kJ mol -1 against 25 kJ mol -1 in pure TFE and 41 kJ mol -1 in H 2 O (Fig. 1)) indicates also the change in the nucleophile at this solvent composition.…”

“…[14] MeOH is stronger nucleophile and weaker base than EtOH, Pr n OH and Pr i OH. Therefore, the addition of EtOH, Pr n OH and Pr i OH to MeOH first increases the observed rate constant of the carbocation decay because of the acceleration of the second step due to an increase in the solvent basicity, but as the concentration of MeOH decreases, the rate constant decreases due to a decrease in the solvent nucleophilicity.…”

“…The reaction is very sensitive to a solvent both in the photochemical step of the carbocation generation and in the step of the nucleophilic addition of a solvent . The rate constants of the decay for the carbocations from DHQ in mixed alcohol–alcohol or alcohol–water binary solvents depend nonlinearly on the solvent composition that was accounted for by the joint effect of the solvent nucleophilicity and basicity on the reaction rate . In binary mixtures of MeOH with EtOH, Pr n OH and Pr i OH, the dependence of the rate constant of the carbocation decay on the solvent composition has a maximum.…”

Laser flash photolysis study of the decay kinetics of carbocations of 1,2,2,4-tetramethyl-1,2-dihydroquinoline in the porous glass in the presence of methanol

“…1), which is characteristic of the CC generated from 1,2 dihydro quinolines. [15][16][17][18][19] When comparing the absorption intensi ties of the CC at 480 nm in methanol and the triplet state of benzophenone at 525 nm in benzene (quantum yield 100%, molar absorption coefficient 7200 L mol -1 cm -1 ) 27 detected upon the laser photolysis of the corresponding solutions with the same absorbance at the excitation wave length, we obtain the molar absorption coefficient of the CC equal to ∼4000 L mol -1 cm -1 if the quantum yield of the CC is 40%. 18, 19 The kinetics of CC decay is described by a law corre sponding to parallel reactions of the first and second or ders.…”