41912-29-2Relevant academic research and scientific papers
Evidence for significant through-space and through-bond electronic coupling in the 1,4-diphenylcyclohexane-1,4-diyl radical cation gained by absorption spectroscopy and DFT calculations
Ikeda, Hiroshi,Hoshi, Yosuke,Namai, Hayato,Tanaka, Futoshi,Goodman, Joshua L.,Mizuno, Kazuhiko
, p. 9207 - 9215 (2008/12/21)
Photoinduced single-electron-transfer promoted oxidation of 2,5-diphenyl-l,5-hexadiene by using N-methylquinolinium tetrafluoroborate/ biphenyl co-sensitization takes place with the formation of an intense electronic absorption band at 476 nm, which is attributed to the 1,4-diphenylcyclohexane-1,4-diyl radical cation. The absorption maximum (λob) of this transient occurs at a longer wavelength than is expected for either the cumyl radical or the cumyl cation components. Substitution at the para positions of the phenyl groups in this radical cation by CH3O, CH3, F, Cl, and Br leads to an increasingly larger redshift of λob. A comparison of the ρ value, which was obtained from a Hammett plot of the electronic transition energies of the radical cations versus σ+, with that for the cumyl cation shows that the substituent effects on the transition energies for the 1,4-diarylcyclohexane-1,4-diyl radical cations are approximately one half of the substituent effects on the transition energies of the cumyl cation. The observed substitu_ent-induced redshifts of λob and the reduced sensitivity of λob to substituent changes are in accordance with the proposal that significant through-space and -bond electronic interactions exist between the cumyl radical and the cumyl cation moieties of the 1,4-diphenylcyclohexane-1,4-diyl radical cation. This proposal gains strong support from the results of density functional theory (DFT) calculations. Moreover, the results of time-dependent DFT calculations indicate that the absorption band at 476 nm for the 1,4-diphenylcyclohexane-1,4-diyl radical cation corresponds to a SOMO-3-SOMO transition.
Deuterium Isotope Effects on the Carbon-13 Chemical Shifts in 2-Substituted 2-Norbornyl Cations
Servis, Kenneth L.,Domenick, Robert L.,Forsyth, David A.,Pan, Yi
, p. 7263 - 7270 (2007/10/02)
Deuterium isotope effects on 13C chemical shifts have been examined as a function of location of deuterium in the C3-exo or C3-endo positions and as a function of increasing electron demand in the series 2-norbornanone, 2-aryl-2-norb
Substituent Effect on the Stability of Benzyl Cation in the Gas Phase
Mishima, Masaaki,Arima, Kiyoshi,Usui, Satoshi,Fujio, Mizue,Tsuno, Yuho
, p. 1047 - 1050 (2007/10/02)
Chloride ion affinities of substituted benzyl cations in the gas phase have been determined by means of an ICR mass spectrometer.The substituent effect has been analyzed in terms of the LArSr Eq., giving a p=13.6 and r+=1.31.
Stabilities of Carbocations in Solution. 14. An Extended Thermochemical Scale of Carbocation Stabilities in a Common Superacid
Arnett, Edward M.,Hofelich, Thomas C.
, p. 2889 - 2895 (2007/10/02)
Until now, thermodynamic stabilities of carbocations have been limited to (1) relatively stable resonance delocalized ions which are ranked on the pKR scale and (2) relatively unstable aliphatic and alicyclic ions which have been compared in the gas phase by ion cyclotron resonance or by calorimetry in SbF5/SO2ClF superacid at -50 to -120 deg C in our laboratory.The present paper will present an extensive series of new measurements which is designed to close the gap between the stable triarylmethyl cations and the unstable ions so as to put them all on a common energy scale.Carbinols were used as precursors in SbF5/HSO3F/SO2ClF at -40 deg C.As we reported recently (J.Am.Chem.Soc., 104, 3522(1982)), these conditions are necessary to avoid complications which appear to be introduced by ion-pairing when the alcohols are treated with the SbF5/SO2ClF system which was used previously to ionize alkyl chlorides.The results from the present work place 39 typical carbocations representing saturated, secondary, and tertiary, and aliphatic, bicyclic, and substituted cumyl, benzhydryl, and trityl systems on a common scale.Correlations and interpolation equations for relating other measurements in the gas phase and solution will be presented.The results provide useful comparisons of the ?+ and ?C+ scales for correlating carbocation stabilities and provide new data for several classic questions in the field such as the ranking of methyl, phenyl, and cyclopropyl groups for stabilizing ions and also the reactions of carbocations with water.
