Inter-enantiomer conversion dynamics and Johari–Goldstein relaxation of benzophenones

We employ temperature- and pressure-dependent dielectric spectroscopy, as well as differential scanning calorimetry, to characterize benzophenone and the singly-substituted ortho-bromobenzophenone derivative in the liquid and glass states, and analyze the results in terms of the molecular conformations reported for these molecules. Despite the significantly higher mass of the brominated derivative, its dynamic and calorimetric glass transition temperatures are only ten degrees higher than those of benzophenone. The kinetic fragility index of the halogenated molecule is lower than that of the parent compound, and is found to decrease with increasing pressure. By a detailed analysis of the dielectric loss spectra, we provide evidence for the existence of a Johari–Goldstein (JG) relaxation in both compounds, thus settling the controversy concerning the possible lack of a JG process in benzophenone and confirming the universality of this dielectric loss feature in molecular glass-formers. Both compounds also display an intramolecular relaxation, whose characteristic timescale appears to be correlated with that of the cooperative structural relaxation associated with the glass transition. The limited molecular flexibility of ortho-bromobenzophenone allows identifying the intramolecular relaxation as the inter-enantiomeric conversion between two isoenergetic conformers of opposite chirality, which only differ in the sign of the angle between the brominated aryl ring and the coplanar phenyl-ketone subunit. The observation by dielectric spectroscopy of a similar relaxation also in liquid benzophenone indicates that the inter-enantiomer conversion between the two isoenergetic helicoidal ground-state conformers of opposite chirality occurs via a transition state characterized by a coplanar phenyl-ketone moiety.

Halogens in Acetophenones Direct the Hydrogen Bond Docking Preference of Phenol via Stacking Interactions

Phenol is added to acetophenone (methyl phenyl ketone) and to six of its halogenated derivatives in a supersonic jet expansion to determine the hydrogen bonding preference of the cold and isolated 1:1 complexes by linear infrared spectroscopy. Halogenation is found to have a pronounced effect on the docking site in this intermolecular ketone balance experiment. The spectra unambiguously decide between competing variants of phenyl group stacking due to their differences in hydrogen bond strength. Structures where the phenyl group interaction strongly distorts the hydrogen bond are more difficult to quantify in the experiment. For unsubstituted acetophenone, phenol clearly prefers the methyl side despite a predicted sub-kJ/mol advantage that is nearly independent of zero-point vibrational energy, turning this complex into a challenging benchmark system for electronic structure methods, which include long range dispersion interactions in some way.

Halogens in Acetophenones Direct the Hydrogen Bond Docking Preference of Phenol via Stacking Interactions

Phenol is added to acetophenone (methyl phenyl ketone) and to six of its halogenated derivatives in a supersonic jet expansion to determine the hydrogen bonding preference of the cold and isolated 1:1 complexes by linear infrared spectroscopy. Halogenation is found to have a pronounced effect on the docking site in this intermolecular ketone balance experiment. The spectra unambiguously decide between competing variants of phenyl group stacking due to their differences in hydrogen bond strength. Structures where the phenyl group interaction strongly distorts the hydrogen bond are more difficult to quantify in the experiment. For unsubstituted acetophenone, phenol clearly prefers the methyl side despite a predicted sub-kJ/mol advantage which is nearly independent of zero point vibrational energy, turning this complex into a challenging benchmark system for electronic structure methods which include long range dispersion interactions in some way.

Highly Selective Vapor and Liquid Phase Transfer Hydrogenation of Diaryl and Polycyclic Ketones with Secondary Alcohols in the Presence of Magnesium Oxide as Catalyst

MgO has been shown to catalyze an almost quantitative hydrogen transfer from 2-octanol as the hydrogen donor to benzophenone to form benzhydrol, a useful intermediate product in the pharmaceutical industry. The hydrogen transfer from a series of alcohols to the carbonyl group of benzophenone, its ten derivatives, four polycyclic ketones, and 2-naphthyl phenyl ketone was carried out in liquid (LP) or vapor phase (VP). The dependence of reactivity on the structure of the hydrogen donor, reaction temperature, donor-acceptor ratio, amount of catalyst, and the type and position of substituents has been established. For both reaction modes, optimal conditions for selective synthesis of the alcohols were determined and side reactions were investigated. The results indicate that the reactivity of the ketone is suppressed by the presence of a methyl substituent in the ortho position to a much greater extent in LP mode. A scale-up was demonstrated in the liquid phase mode.

Synthesis and Spectroscopic Characterisation of Some Novel Butadienyl Asycyanine Colorants having Lepidine Moiety

Twenty-one novel chromophoric chain β-substituted butadienyl asycyanine colorants have been synthesized by catalytic condensation of (i) dimethylaminostyryl phenyl ketone, (ii) 4ʹ-dimethylaminostyryl-4ʹ-nitrophenyl ketone and (iii) 4ʹ-dimethylaminostyryl-4ʹ-methoxyphenyl ketone with seven lepidinium methyliodide salts in ethanolic DMF medium using piperidine as basic catalyst. These colorants were synthesized with the objective to study the effect of electron acceptor and electron donor group substituent at 4ʹ-position in the chain β-phenyl nucleus on visible absorption maxima. The newly prepared colorants were found to exhibit uniform increase in absorption maxima i.e. Red shift (RS), when collated with analogues having no substituent in the β-phenyl nucleus. Again the absorption maxima of the title colorants were found to be higher than the absorption maxima of previously prepared butadienyl colorants having quinoline mioety of same conjugated system.