56683-69-3Relevant articles and documents
Bimolecular hydrogen abstraction from phenols by aromatic ketone triplets
Lathioor, Edward C.,Leigh, William J.
, p. 291 - 300 (2008/02/05)
Absolute rate constants for hydrogen abstraction from 4-methylphenol (para-cresol) by the lowest triplet states of 24 aromatic ketones have been determined in acetonitrile solution at 23°C, and the results combined with previously reported data for roughly a dozen other compounds under identical conditions. The ketones studied include various ring-substituted benzophenones and acetophenones, α,α,α-trifluoroacetophenone and its 4-methoxy analog, 2-benzoylthiophene, 2-acetonaphthone, and various other polycyclic aromatic ketones such as fluorenone, xanthone and thioxanthone, and encompass n,π*, π,π*(CT) and arenoid π,π* lowest triplets with (triplet) reduction potentials (Ered*) varying from about -10 to -38 kcal mol-1. The 4-methylphenoxyl radical is observed as the product of triplet quenching in almost every case, along with the corresponding hemipinacol radical in most instances. Hammett plots for the acetophenones and benzophenones are quite different, but plots of log log kQ vs Ered* reveal a common behavior for most of the compounds studied. The results are consistent with reaction via two mechanisms: a simple electron-transfer mechanism, which applies to the n,π* triplet ketones and those π,π* triplets that possess particularly low reduction potentials, and a coupled electron-/proton-transfer mechanism involving the intermediacy of a hydrogen-bonded exciplex, which applies to the π,π* ketone triplets. Ketones with lowest charge-transfer π,π* states exhibit rate constants that vary only slightly with triplet reduction potential over the full range investigated; this is due to the compensating effect of substituents on triplet state basicity and reduction potential, which both play a role in quenching by the hydrogen-bonded exciplex mechanism. Ketones with arenoid π,π* states exhibit the fall-off in rate constant that is typical of photoinduced electron transfer reactions, but it occurs at a much higher potential than would be normally expected due to the effects of hydrogen-bonding on the rate of electron-transfer within the exciplex.
Oxonium Ions. Solvation by Single Acetonitrile Molecules in the Gas Phase and by Bulk Solvents
Bromilow, J.,Abboud, J. L. M.,Lebrilla, C. B.,Taft, R. W.,Scorrano, G.,Lucchini V.
, p. 5448 - 5453 (2007/10/02)
The standard free energy of formation of gaseous complexes between monoprotonic oxonium ions and acetonitrile have been obtained by using the ion cyclotron resonance equilibrium constant method for exchange of acetonitrile between the ions.The results show that the "solvation" by a single molecule of acetonitrile in the gas phase reproduces the important diverse effects of molecular structure on oxonium ion solvation by bulk water.It is estimated from the present results that the effects of solvation by bulk water are only about three times as great as the corresponding effects of "solvation" by a single water molecule in the gas phase.Internal charge delocalization from the protonic site of the oxonium ions may be reversed by differential solvation, both with single H-bonding molecules in the gas phase and with bulk solvent.Further evidence for the site of preffered protonation of esters and amides is provided.
