59502-05-5

It is shown that lyotropic liquid crystal mixtures made of poly-γ-benzyl-l-glutamate (PBLG) dissolved in N,N-dimethylformamide (DMF) are efficient anisotropic NMR solvents to distinguish the enantiomers of chiral amines through the effects of the differential ordering of enantiomers. This type of solvent overcomes problems often encountered when dissolving amines into the more conventional PBLG/CHCl3 or PBLG/CH2Cl2 liquid crystals. Furthermore, it is shown that perdeuterobenzyl chloride is an excellent achiral deuterated derivatizing agent for enantiomeric excess measurements of chiral amines in conjunction with the PBLG/DMF solvent.

The first reversible N-heterocyclic carbene (NHC) induced α-H abstraction in tungsten(VI) imido-dialkyl dialkoxide complexes is reported. Treatment of W(NAr)(CH2Ph)2(OtBu)2 (Ar=2,6-dichlorophenyl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl) with different NHCs leads to the formation of complexes of the type W(NAr)(CHPh)(NHC)(CH2Ph)(OtBu) in excellent isolated yields of up to 96 %. The highly unusual release of the tert-butoxide ligand as tBuOH in the course of the reaction was observed. The formed alkylidene complexes and tBuOH are in an equilibrium with the NHC and the dialkyl complexes. Reaction kinetics were monitored by 1H NMR spectroscopy. A correlation between the steric and electronic properties of the NHC and the reaction rates was observed. Kinetics of a deuterium-labeled complex in comparison to its non-deuterated counterpart revealed the presence of a strong primary kinetic isotope effect (KIE) of 4.2, indicating that α-H abstraction is the rate-determining step (RDS) of the reaction.

The photochemistry of dibenzyl ketone (DBK) and other molecules capable of producing benzyl radicals and substituted benzyl radicals has been investigated in micellar systems.The cage effect (percent of unscavengeable radical pairs produced by photolysis) was measured under a variety of conditions, and the results are compared with those obtained in homogeneous organic solvents.For example, parameters such as mean occupancy of ketone, detergent type and concentration, O2 concentration, additives, temperature, applied magnetic field, and pressure have been varied and investigated as to their influence on the magnitude of cage effect.In addition to modifying its environment, structural modification of the DBK by incorporation of 2H and 13C isotopes, hydrophobic groups, and heavy atoms was performed to investigate the impact of these variations on the cage effect in micellar systems.Isotopic substitution of 2H or 13C leads to results on both the quantum yields for reactions and on the percent cage that were consistent with expectations of magnetic isotope effects.Hydrophobic groups substituted in the 4-position of DBK were found to cause a substantial increase in the cage effect and yet retain the magnetic-field-dependent character found in the parent DBK.Incorporation of Br in the 4-position of DBK was found to enhance the cage effect but at the same time cause the cage effect to become magnetic field independent.Substitution of α-naphthyl for phenyl in DBK also produced magnetic-field-independent behavior, in addition to a dramatic decrease in the efficiency of photolysis.

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.

The free-radical chlorination of meta- and para-substituted toluenes, ethylbenzene, and cumenes by phenylchloroiodonium chloride was investigated by the method of competing reactions.The good correlation between the relative reaction rate constants and the Brown ?+ constants and also the large negative values of ρ indicate separation of charges in the transition state.The values of the primary kinetic isotope effects of hydrogen decrease with increase in the reactivity of the substrate, whereas the values of the reaction parameters vary irregularly.The deviations from the inverse relation between the reactivity and the selectivity are due to the polar character of the transition state.

Matrix photoionization of dilute fluorotoluene samples produced relatively sharp photosensitive absorptions in good agreement with gas-phase photodissociation spectra for ring-substituted fluorotoluene parent cations.The benzyl chloride parent cation form was observed as a sharp, photosensitive 469.3 nm band in both benzyl chloride and p-chlorotoluene experiments, whereas chlorotoluene cations gave broad absorption with little photolysis.Experiments with o- and p-fluorotoluene produced parent cation absorption, which were considerably sharper than the gas-phase PDS, and the matrix absorptions exhibited vibrational structure.Benzyl and substituted benzyl radicals were also observed in these experiments.