39194-34-8Relevant academic research and scientific papers
Direct observation of a doubly destabilized cation
Afifi, Hanan,Mikhailine, Alexandre,Mladenova, Gabriela,Chtchemelinine, Andrei,Sultana, Israt,Dyblenko, Tatiana,Danilov, Evgeny,Fournier, Rene,Lee-Ruff, Edward
experimental part, p. 343 - 354 (2012/07/03)
The 9-fluorenyl cation is a member of the 4N Hueckel antiaromatic series of intermediates, first observed by time-resolved spectroscopy on UV photo-excitation of 9-fluorenol.[1] 9-Trifluoromethyl-9-fluorenol incorporating an electron-withdrawing substituent was subjected to preparative and laser flash photolysis. Photoproduct studies in methanol indicated products derived from the corresponding fluorenyl cation and radical intermediates. Time-resolved spectroscopy in hexafluoroisopropanol (HFIP) showed a transient which was assigned to the corresponding cation as evident from methanol quenching. The lifetimes and methanol quenching rates of this transient was compared with that of 9- methylfluorenyl cation. The kinetic stabilities of these ions were compared to thermodynamic parameters obtained from theoretical calculations. ARKAT-USA, Inc.
Substituent Effects on the C-C Bond Strength, 15. Geminal Substituent Effects, 7. Thermochemistry and Thermal Decomposition of Alkyl-substituted Tricyanomethyl Compounds
Rakus, Klaus,Verevkin, Sergej P.,Beckhaus, Hans-Dieter,Ruechardt, Christoph
, p. 2225 - 2234 (2007/10/02)
The thermolysis reactions of the tricyanomethyl compounds 10a-c were studied in solution. 2,2-Dicyano-3-methyl-3-phenylbutyronitrile (10a) and 2,2-dicyano-3-methyl-3-(4-nitrophenyl)butyronitrile (10b) decomposed heterolytically into carbenium ions and (CN)3C(-) anions, while 9-methyl-9-(tricyanomethyl)fluorene (10c) underwent about 11percent homolytic C-C bond cleavage into 9-methyl-9-fluorenyl- and tricyanomethyl radicals.The rates of the homolysis were determined by a radical scavenger procedure under conditions of pseudozero order kinetics.From the temperature effect on the rate constants the activation parameters were determined -1, ΔS(excit.) (10c) = 58 +/- 5 J mol-1 K-1>.Standard enthalpies of formation ΔHf0 (g) were determined for 2,2-dicyanopropionitrile (2) (422.45 kJ mol-1), 2,2-dicyanohexanenitrile (3) (349.74 kJ mol-1), 2,2-dicyano-3-phenylpropionitrile (4) (540.75 kJ mol-1), 2-butyl-2-methylhexanenitrile (5) (-133.20 kJ mol-1), 2,2-dimethylpentanenitrile (6) (-45.78 kJ mol-1), and 2-methylbutyronitrile (7) (2.44 kJ mol-1) from the enthalpies of combustion and enthalpies of sublimation/vaporization.From these data and known ΔHf0 (g) values for alkanenitriles and -dinitriles, thermochemical increments for ΔHf0 (g) were derived for alkyl groups with one, two, or three cyano groups attached.The comparison of these increments with those of alkanes reveals a strong geminal destabilization, which is interpreted by dipolar repulsions between the cyano groups. - From ΔHf0 (g) of 10c and ΔH(excit.) of its homolytic decomposition the radical stabilization enthalpy for the tricyanomethyl radical 1 RSE (1) = -18 kJ mol-1 was determined.Thus, 1 is destabilized, in comparison with the RSEs of tertiary α-cyanoalkyl (23 kJ mol-1) and α,α-dicyanoalkyl (27 kJ mol-1) radicals, which were recalculated from bond homolysis measurements and the new thermochemical data.This change of RSE on increasing the number of α-cyano groups is discussed as the result of the additive contributions by resonance stabilization and increasing destabilization by dipolar repulsion.The amount of the dipolar energies was estimated by molecular mechanics (MM2). - Key Words: Enthalpies of formation / Geminal substituents, energetic interaction of / Bond cleavage, C-C, kinetics of / Radicals, stability of / Increments, thermochemical, of cyanides / Bond strength, substituent effects on
Contrasting Photosolvolytic Reactivities of 9-Fluorenol vs 5-Suberenol Derivatives. Enhanced Rate of Formation of Cyclically Conjugated Four ? Carbocations in the Excited State
Wan, Peter,Krogh, Erik
, p. 4887 - 4895 (2007/10/02)
The photosolvolysis of 9-fluorenol (1) and several of its derivatives, as well as related systems, has been studied in aqueous methanol and acetonitrile solutions.The primary aim of this study was to examine the effect of the internal cyclic array (ICA) of these compounds in promoting photosolvolysis with respect to the number of ? electrons available in the ICA.It was observed that 9-fluorenol derivatives photosolvolyze much more efficiently than any of the related systems studied in this work.In contrast, ground-state 9-fluorenol derivatives are the least reactive systems with respect to solvolysis.Quantum yields for methyl ether formation for photosolvolysis in 50percent MeOH-H2O are reported for 1-3.Rate constants for solvent-assisted photodehydroxylation (ks) are calculated on the basis of the proposed mechanism of heterolytic C-OH bond rupture in the primary photochemical step and are in the range (1.3-1.6)x1E10 s-1 for 1-3.
