111359-34-3Relevant academic research and scientific papers
Remarkable kinetic stability of α-thiocarbamoyl substituted 4-methoxybenzyl cations
McClelland, Robert A.,Licence, Victoria E.,Richard, John P.,Williams, Kathleen B.,Lin, Shrong-Shi
, p. 1910 - 1915 (1998)
4-Methoxybenzyl cations bearing α-(N,N-dimethylcarbamoyl) and α-(N,N-dimethylthiocarbamoyl) substituents have been generated photochemically upon irradiation of precursors with pentafluorobenzoate or 4-methoxybenzoate leaving groups. The ions have been observed with flash photolysis in 40:60 acetonitrile:water and in 50:50 methanol:water, and rate constants were measured for their decay in solvent alone and for their capture by azide ion. The cations so studied and their lifetimes in 40% acetonitrile are 6, ArC+H-CONMe2, 0.6 μs; 2, ArC+H-CSNMe2, 7 ms; and 4, ArC+(CH3)-CSMe2 6 ms, where Ar = 4-MeOC6H4. The cation 4 reacts with solvent by elimination of a proton from the α-methyl group, and the rate constant for solvent addition must be less than 1 s-1. The CSNMe2 substituted cations are 105-107-fold longer lived than analogs where the thioamide group has been replaced with an α-methyl. The UV-visible absorption spectra of these two cations also show significant differences from those of typical 4-methoxybenzyl cations. Thus, both the lifetimes and spectra point to a strong interaction of the benzylic centre with the thioamide group.
How does organic structure determine organic reactivity? Nucleophilic substitution and alkene-forming elimination reactions of α-carbonyl and α-thiocarbonyl substituted benzyl derivatives
Richard, John P.,Lin, Shrong-Shi,Buccigross, Jeanne M.,Amyes, Tina L.
, p. 12603 - 12613 (2007/10/03)
The effect of α-(N,N-dimethylcarbamoyl) and α-(N,N-dimethylthiocarbamoyl) substituents on the rate constants for partitioning of α-substituted 1-(4-methoxyphenyl)ethyl carbocations between nucleophilic addition of 50:50 (v:v) MeOH/H20 (k(s), s-1) and deprotonation by this solvent (k(e), s-1) have been investigated. The data show that these α-amide and α-thioamide substituents result in 80-fold and ≤ 30000-fold decreases, respectively, in k(s) for capture of the 4-methoxybenzyl carbocation by solvent, but that they lead to much smaller changes in k(e), for deprotonation of the corresponding α-substituted 1-(4-methoxyphenyl)ethyl carbocations by solvent. The large effect of the α-thioamide substituent on the partitioning of α-substituted 1-phenylethyl carbocations between formation of the products of solvolysis and elimination is therefore due primarily to the effect of this α-substituent on k(s), for capture of the carbocation by solvent. The results of experimental and computational studies are consistent with the conclusion that the relative magnitude of the rate constants k(s) and k(e) for partitioning of α-substituted 1-phenylethyl carbocations is strongly controlled by the relative thermodynamic stabilities of the neutral products of these reactions.
DESTABILIZED CARBOCATIONS. NUCLEAR MATNETIC RESONANCE DETECTION AND REACTIVITIES OF ARYL α-THIOFORMAMIDYL CATIONS
Ablenas, F. J.,George, B. E.,Maleki, M.,Jain, R.,Hopkinson, A. C.,Lee-Ruff, E.
, p. 1800 - 1803 (2007/10/02)
A series of α-aryl and diarylthioformamidyl cations were observed by low-temperature nuclear magnetic resonance spectroscopy.These ions undergo efficient cyclization and deprotonation to give benzothiophenes.
