F:Flammable;
108-87-2Relevant academic research and scientific papers
Ionization Energies and Entropies of Cycloalkanes. Kinetics of Free Energy Controlled Charge-Transfer Reactions.
Sieck, L. Wayne,Mautner, Michael
, p. 3646 - 3650 (1982)
Enthalpies and entropies of ionization (ΔH0ion and ΔS0ion) of alkylcyclohexanes, as well as cycloheptane, cyclooctane, and trans-Decalin, have been determined by charge-transfer equilibrium measurements.Values of ΔHion, in units of kcal mol-1 (or eV), range from 229.6 (9.96) for cycloheptane to 210.7 (9.14) for trans-Decalin.A major effect of alkyl substitution is observed following substitution at a site α to a tertiary hydrogen atom (as from methylcyclohexane to 1,2-dimethylcyclohexane), or following replacement of a tertiary hydrogen atom (as from methylcyclohexane to 1,1-dimethylcyclohexane).In both cases, ΔH0 ion decreases by ca. 5 kcal mol-1.Entropies of ionization are near zero for alkylcyclohexanes but range up to 5 cal deg-1 mol-1 for nonsubstituted cycloalkanes (cyclooctane).The charge-transfer reactions involving the cycloalkanes are shown to be fast processes; i.e., the sum of the reaction efficiencies (r=k/kcollision) of the forward and reverse processes is near unity.The efficiencies of these processes appear to be determined uniquely by the overall free energy change (or equilibrium constant K).Specifically, the reaction efficiencies are defined, within a factor of 2 by the relation r=K/(1+K), which can be justified by using transition-state theory applied to the decomposition of a collision complex over surfaces lacking energy barriers.These reactions are defined as intrinsically fast processes in that they are slowed only by the overall reaction thermochemistry and not by any properties or reactions of the intermediate complex.
The Radical Cation of Methylcyclohexane
Katsumura, Y.,Azuma, T.,Quadir, M. A.,Domazou, A. S.,Buehler, R. E.
, p. 12814 - 12821 (1995)
It is shown by pulse radiolysis that the transient absorption in N2O-saturated or CO2-saturated methylcyclohexane (MCH), peaking at about 570 nm, is due to the solvent radical cation MCH+.From simulations with the semiempirical t-0.6 rate law, it is concluded that MCH+ is of very high mobility: at 133 K (supercooled liquid) Dexp = (1.06 +/- 0.2) x 10-6 cm2 s-1, which is ca. 400 times faster than expected from diffusion.At room temperature MCH+ is about 11 times faster than diffusion, and this is in perfect agreement with the conductivity of MCH+, as measured by Warman et al.For the high mobility of MCH+ an activation energy of 8.9 +/- 0.3 kJ/mol is found.The rate constant for scavenging MCH+ with norbornadiene (NBD) is k2(133 K) = (1.8 +/- 0.5) x 108 M-1 s-1.This is again 80 times faster than the diffusional rate constant.From the intercepts of the semiempirical t-0.6 linearity plots, the free ion spectra were derived.The free ion absorbance at 133 K turns out to be 2.0 times smaller than that at room temperature.The free ion yield at low temperatures therefore was derived to be Gfi(127-153 K) = 0.06 +/- 0.015 (100 eV)-1.From the free ion intercept at room temperature the absorption coefficient ε was determined: ε570nm(MCH+) >/= 2300 M-1 cm-1.Without the electron scavengers N2O or CO2 the olefinic cation methylcyclohexene+ is found to replace MCH+.This indicates that some excited species, usually quenched by N2O or CO2, is the precursor of the high-mobility radical cation MCH+.
Radical Cations of Cyclohexanes Alkyl-substituted on One Carbon: An ESR Study of the Jahn-Teller Distorted HOMO of Cyclohexane
Shiotani, Masaru,Lindgren, Mikael,Ohta, Nobuaki,Ichikawa, Takahisa
, p. 711 - 719 (2007/10/02)
Cation radicals of cyclohexanes alkyl-substituted on one carbon have been stabilized in perfluoromethylcyclohexane and other halocarbon matrices at 4.2 K and studied by means of ESR spectroscopy.It was found that all have an electronic ground state resembling the 2Ag state of the cyclohexane cation, one of the possible states following a Jahn-Teller distortion of the D3d cyclohexane chair structure.The cations can be classified into two groups depending on the substituted alkyl group.To the first group belong the cations with a methyl group or a primary carbon (ethyl, n-propyl or isobutyl group) attached to the ring.The disubstituted cyclohexane cations of 1,1-dimethylcyclohexane and 1-methyl-1-ethylcyclohexane were also found to have a similar structure.The ESR spectra are characterized by a 1:2:1 three-line pattern with the hyperfine (hf) splitting due to two magnetically equivalent equatorial ring hydrogens.The magnitude of the splitting was found to depend on the size and number of substituents, ranging from 74 G (methylcyclohexane.+) to 55 G (isobutylcyclohexane.+).An additional doublet, 17-34 G, due to a hydrogen on the substituent could be detected in certain cases.Such hydrogens are axial with one of the elongated C-C bonds in the ring structure which contains a relatively large fraction of the unpaired electron.It follows that the substituents are located asymmetrically with respect to an ag-like SOMO in the ring.In the second group a secondary or tertiary carbon connects the substituent to the ring, such as an isopropyl or tert-butyl group.The largest hf splittings are ca. 30 G in magnitude, due to certain hydrogens on the substituent which are axial with respect to the cyclohexyl bond.It follows that an ag-like SOMO in the ring here is symmetrically arranged with respect to the position of the substituent.Hyperconjugation is the dominating mechanism for the spin transfer in all cations reported in this study.
Mirror Inversion of the Low-symmetry Ground-state Structures of the Methylcyclohexane and 1,1-Dimethylcyclohexane Radical Cations
Sjoeqvist, Lars,Lindgren, Mikael,Lund, Anders,Shiotani, Masaru
, p. 3377 - 3382 (2007/10/02)
The dynamics of the methylcyclohexane and 1,1-dimethylcyclohexane radical cations in a solid perfluoromethylcyclohexane matrix at low temperature have been studied by electron paramagnetic resonance (EPR) spectroscopy.The reversible variations of the experimental EPR linewidth, observed for both cations in the temperature region 4-173 K, have been reproduced through simulations employing a dynamical model for the molecular motion.It was assumed that an interconversion between two energetically equivalent mirror images of the molecular framework occurred.The related activation energy has been determined to be 0.2 and 0.3 kcal mol-1 for the methylcyclohexane and 1,1-dimethylcyclohexane radical cations, respectively.
