71013-72-4Relevant academic research and scientific papers
Effect of the internal rotation of the CHD2 group on the aliphatic CH stretching mode of the toluenes C6H5CHD2 and C6D5CHD2 in solid crystalline phases
Cavagnat, D.,Lascombe, J.
, p. 4336 - 4348 (1982)
The infrared and Raman spectra of the toluenes C6H5CHD2 and C6D5CHD2 in the aliphatic CH stretching mode range have been recorded in a large temperature range (17 to 175 K) for both crystalline phases α and β.At very low temperature, the β form spectra show three bands; each of them is assigned to the vibration of a CH oscillator localized in a different site.Three groups of bands are also observed in the α phase spectra: a single band at higher frequency and two doublets at lower frequency.This splitting is assigned to the existence of two types of molecules in the unit cell, involving six different CH vibrators.A quantum theory of these spectra is carried out, assuming an anharmonic coupling of the CH stretching mode with the CHD2 torsion.As a consequence of this coupling, in the adiabatic approximation, the vibrational energy depends on the conformation and can be considered as an additional torsional potential.This latter has no ternary symmetry so that the total torsional potential has three princopal unequal wells that correspond to three different locations of the CH oscillator.Therefore, no tunneling effect appears, which is in agreement with the classical interpretation.Furthermore, this theory ascribes the temperature dependence of the relative intensities of the νCH bands to the population density of the first torsional levels in the vibrational ground state and suggests that, at very low temperature, the isotopic system gets ordered.At higher temperature, a strong relaxation of the νCH vibration bands is observed.This relaxation is much stronger than that of the aromatic ring modes.Thus the relaxation process is essentially due to the influence of the anharmonic coupling between the CH stretching mode and the τCHD2 mode.Two mechanisms are considered: the first one involves Markovian jumps of the system from an equilibrium position to another one, the second one involves fluctuations of the CH vibration around each of these equilibrium positions.NMR and neutron scattering data have already been analyzed on the basis of the first process.Starting from the residence times so determined, the computations show that this mechanism is an efficient relaxation process, but indicate that it is not sufficient to fit the experimental profiles.This fit is obtained rather by using the second model with parameters of reasonable physical values; thus, the second process is also efficient.A better treatment of the relaxation process would be to elaborate; it would have to include both mechanisms and to take into account motions of the methyl group with different amplitudes.
Formation of D Atoms in the Pyrolysis of Toluene-d8 behind Shock Waves. Kinetics of the Reaction C7D8 + H -> C7D7H + D
Rao, V. Subba,Skinner, Gordon B.
, p. 4362 - 4365 (2007/10/02)
Dilute mixtures (5-20 ppm) of toluene-d8 in argon were pyrolyzed behind reflected shock waves at temperatures of 1410-1730 K and total pressures of 3 atm.In a second group of experiments, mixtures of 20 ppm toluene-d8 and 5 ppm neopentane (which acted as a source of H atoms) were similarly pyrolyzed at 1200-1460 K.Progress of the reaction was followed by analysis for H and D atoms by using resonance absorption spectroscopy.For the reaction C6D5CD3 -> C6D5CD2 + D under the experimental conditions, k1D = 1.1 x 1E14 exp(-82000 cal/RT) s-1.After allowance for isotope effects and unimolecular falloff, the high-pressure rate constant for the reaction C6H5CH3 -> C6H5CH2 + H is calculated to be k1, infinite = 2.7 x 1E14 exp(-83000 cal/RT) s-1 over the range 1000-1800 K.Estimated uncertainties are a factor of 1.5 in k1D and 2 in k1, infinite.For the reaction D + C6D5CD3 -> C6D5CD2 + D2, k2D2 = 2.1 x 1E15 exp(-15000 cal/RT) mol-1 cm3 s-1 over the range 1300-1800 K, with an uncertainty of a factor of 1.5, while after correction for isotope effects the rate constant for H + C6H5CH3 -> C6H5CH2 + H2 over the range 600-1800 K can be expressed by the non-Arrhenius equation k2 = 7.6 x 1E-5T5.5 exp(-340 cal/RT) mol-1 cm3 s-1, with an uncertainty of a factor of 2.Data were also obtained on the exchange reaction by which H atoms add to the ring of C6D5CD3, and D atoms are eliminated.For this reaction k4D = 3.5 x 1E13 exp(-3700 cal/RT) mol-1 cm3 s-1 in the range 1200-1500 K, with an estimated uncertainty of a factor of 1.5.
