Raman Spectroscopic Study on the Solvation of p-Aminobenzonitrile in Supercritical Water and Methanol

Abstract

Raman spectra of the C[triple bond]N stretching vibration of p-aminobenzonitrile (ABN) have been investigated in water, methanol, and cyclohexane under sub- and supercritical conditions, and in acetonitrile under subcritical condition. In all solvent fluids covering the supercritical region, the vibrational frequency of the C[triple bond]N stretching mode decreased with increasing solvent density from the gaseous region to the medium density region rho(r) approximately = 2, where rho(r) is the reduced density by the critical density of the solvent. However, from the medium density region to the higher density region, the vibrational frequency turned to increase with the solvent density. The temperature-induced low frequency shift of the C[triple bond]N stretching Raman band was also ascertained by the measurement of the temperature dependence of Raman spectrum of ABN vapor above 543 K. The electronic absorption spectra in the UV region of ABN were also measured under the same experimental conditions. The absorption peak energies decreased with an increase of the solvent density, except in water above rho(r) = 2.8. The vibrational frequency shift in cyclohexane was explained by a sum of contributions of the repulsive interaction, the mean field attractive interaction, and the pure temperature effect probably due to the hot-band contribution. The residual frequency shift after the subtraction of the repulsive and temperature effects in water and methanol showed the low frequency shift with increasing solvent density from rho(r) congruent with 0 to 2.8. However, above rho(r) congruent with 2.8 in water, the residual shift showed a high frequency shift with increasing solvent density. The electronic state calculations based on the PCM model using the density functional theory (DFT) indicated that the solvent polarity change caused the low frequency shift of the C[triple bond]N stretching mode, which was also correlated with the shift of the electronic absorption spectrum. The results of the DFT calculations on the cluster of ABN with water molecules and the molecular dynamics simulations indicated that the high frequency shift of the C[triple bond]N stretching mode in water above rho(r) congruent with 2.8 could be due to the hydrogen bonding between water and ABN.

Solute–solvent hydrogen-bonding in room temperature ionic liquids studied by Raman spectroscopy

“…The reference for the experimental results is 3423.9 cm À1 , which was obtained in the gaseous phase. 20 As is shown in the table, a simple 1 : 1 cluster model reproduces the experimental results fairly well; i.e. the anion effect ordering is similar, except for the NTf 2 À and Nf 2 À anions.…”

“…According to previous studies, the NH 2 stretching vibration of ABN or p-nitroaniline (pNA) is mainly affected by hydrogen-bonding between the solute and solvent, and the shift may be a good indicator of the hydrogen-bond accepting ability of the solvent (the b value). 19,20 On the other hand, the CN stretching vibration is affected by several factors and its solvent dependence is rather complicated. [21][22][23] The vibrational frequency is affected by solute-solvent repulsive interactions, dipole-dipole interactions, direct hydrogenbonding between the -CN site and the solvent molecule, and indirectly by hydrogen-bonding between the -NH 2 site and the solvent molecule.…”

Universality of Viscosity Dependence of Translational Diffusion Coefficients of Carbon Monoxide, Diphenylacetylene, and Diphenylcyclopropenone in Ionic Liquids under Various Conditions

“…23,24 The temperature of the cell was controlled by cartridge heaters immersed into the brass block and a PID regulator. For the measurements of the TG signal in mixture solvents, the solution was kept in a quartz cell of 1 cm path length, and the measurements were performed at room temperature (typically 23°C).…”

Microhydrated aromatic cluster cations: Binding motifs of 4-aminobenzonitrile-(H2O)n cluster cations with n ≤ 4

“…45 In contrast to the ABN-H 2 O dimer, spectroscopic and quantum chemical information on larger neutral ABN-(H 2 O) n clusters is rather scarce, and limited to the ABN-(H 2 O) 2 trimer. 20,46 The reported REMPI spectrum of ABN-(H 2 O) 2 exhibits a single electronic origin band but no isomer assignment was offered. 20 Low-level B3LYP/6-31+G* calculations 46 suggest that the by far most stable ABN-(H 2 O) 2 isomer has one NH-bound ligand and one linear CN-bound ligand.…”