Intra- and intermolecular H-bond mediated tautomerization and dimerization of 3-methyl-1,2-cyclopentanedione: Infrared spectroscopy in argon matrix and CCl4 solution

Valorization of Vine Prunings by Slow Pyrolysis in a Fixed-Bed Reactor

The paper aimed at studying the slow pyrolysis of vine pruning waste in a fixed bed reactor and characterizing the pyrolysis products. Pyrolysis experiments were conducted for 60 min, using CO2 as a carrier gas and oxidizing agent. The distribution of biochar and bio-oil was dependent on variations in heat flux (4244–5777 W/m2), CO2 superficial velocity (0.004–0.008 m/s), and mean size of vegetal material (0.007–0.011 m). Relationships among these factors and process performances in terms of yields of biochar (0.286–0.328) and bio-oil (0.260–0.350), expressed as ratio between the final mass of pyrolysis product and initial mass of vegetal material, and final value of fixed bed temperature (401.1–486.5 °C) were established using a 23 factorial design. Proximate and ultimate analyses, FT-IR and SEM analyses, measurements of bulk density (0.112 ± 0.001 g/cm3), electrical conductivity (0.55 ± 0.03 dS/m), pH (10.35 ± 0.06), and water holding capacity (58.99 ± 14.51%) were performed for biochar. Water content (33.2 ± 1.27%), density (1.027 ± 0.014 g/cm3), pH (3.34 ± 0.02), refractive index (1.3553 ± 0.0027), and iodine value (87.98 ± 4.38 g I2/100 g bio-oil) were measured for bio-oil. Moreover, chemical composition of bio-oil was evaluated using GC-MS analysis, with 27 organic compounds being identified.

Impact of donor acidity and acceptor anharmonicity on vc=o spectral shifts in O-H···O=C H-bonded ketone-alcohol complexes: An IR spectroscopic investigation

O-H···O=C Hydrogen bonding (H-bonding) results in spectral shifts in both ν_O-H and ν_C=O modes. A large number of investigations exist in literature that focuses on how the spectral shifts vary with certain properties of the donors and acceptors. However information on how the magnitude of spectral shift is dictated individually by the donor and acceptor is not yet clear to us. Here, IR spectroscopy in room temperature CCl₄ solution has been used to investigate how ν_C=O spectral shifts of ketones in H-bonded complexes with alcohols are influenced by change in donor and acceptor properties. For this purpose 25 number of O-H···O=C H-bonded complexes formed by 5 different ketones and 5 alcohols have been studied. The magnitude of red-shifts shown by the ν_C=O bands were found to show systematic trends with changing donor and acceptor species. It was found that for a particular ketone, the magnitude of shift increases monotonically with acidity of the alcohols. Spectral shifts were found to increase in a linear fashion with decreasing p^K_a of the donor alcohols. On the other hand, when the alcohol were kept fixed, the spectral shift was found to be dependent on the CO bond strength of the ketones. We found spectral shifts to linearly increase with increasing anharmonicity constant and decreasing dissociation energy of CO bond. Finally, it has been shown that there exist concomitant correlations of the spectral shifts with donor p^K_a and acceptor ν_C=O anharmonicity constant/bond dissociation energy. The relations have been validated for H-bonded complexes of 1,4-cyclohexanedione with the above mentioned five alcohols.

Cooperative effect on phenolic νO-H frequencies in 1:1 hydrogen bonded complexes of o-fluorophenols with water: A matrix isolation infrared spectroscopic study

Matrix isolation infrared spectra of 1:1 complexes of two ortho-fluorophenols, 2-fluorophenol (2-FPh) and 2,6-difluorophenol (2,6-DFPh), with water and benzene have been analyzed in combination with electronic structure calculations to investigate cooperative effect in O-H···O-H···F hydrogen bonded linkage, which manifests as large spectral shifts of the phenolic O-H stretching fundamental. Calculation predicts that a nearly planar cyclic geometry is preferred by the binary water complexes of the syn conformer of 2-FPh as well as 2,6-DFPh, and the observed spectral shifts are in good agreement with the predicted shifts for such conformers. On the other hand, for other possible isomeric structures, the molecular plane of water moiety is oriented perpendicular to that of the fluorophenols, and the observed as well as predicted shifts are smaller than those of the ortho substituted fluorophenols, although the total binding energies are predicted to be larger for the former. The observed spectral shifts are however consistent with local interaction energy parameters, like hyperconjugative charge transfer and accumulation of electron density (ρ) along the O-H···O hydrogen bond path. For the binary O-H···π hydrogen bonded benzene complexes of the fluorophenols, where cooperative interaction is not possible, the observed shifts are consistent with the conformers preferred according to total binding energies as well as local charge transfer effects of the complexes.